I have an 87 XJ 4.0L that appears to be getting air into the closed loop
system. Here is the scenario that I have played out about 5 times now,
with replacing a myriad of parts, and the emptying of my wallet!

1. Lift rear of vehicle by driving up on ramps.

2. Fill system reservoir with 50/50 mix leaving cap off.

3. Unthread temp sending unit from to allow air to escape system. I
continue this until only coolant comes out of the threads. I make sure
to maintain coolant in the reservoir during this process.

4. Tighten up temp sending unit.

5. Make sure reservoir is filled up to about the halfway mark (the
molding line) and screw cap back on tightly.

6. Start up engine and bring up to operating temperature.

7. Cooling system works great and holds temp at about 180F. I drive it
around hard trying to get it to run hot, never moves above 185F.

8. Take it home and declare problem fixed and park the vehicle.

9. Next day start it up and drive it and bring it up to "normal"
operating temp but notice that it is now 200F and when I come to a stop
the temp starts creeping to 220F, but drops again when I start driving.

10. Take it home and park it and hear hissing from the reservoir. I let
it cool down completely, assuming that I possibly had too much coolant
in the system and it is just purging itself.

11. Start it up the next day and it start running even hotter and
completely overheats whenever I come to a stop. I check the reservoir,
and lo and behold, I have air in the system again and it has forced my
coolant back out through the reservoir cap.

12. Go back to step 1. Grrrr....

I have replaced the following to no avail, but my mechanic loves me!

Radiator - Assumption was a blocked rad, which was actually correct but
not the source of the problem!

Temperature Sending Unit - Old one was acting erratically according to
mechanic. I never had a problem with it, but he showed me the
multimeter readings...

Thermostat - Actually three of them now, just to be sure.

Thermostat Housing - Apparently, all of those thermostat changes cracked
the housing.

Reservoir Cap - Could it be THAT easy?!??! Of course not.

Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
prove it!

They have also checked the head gasket by performing compression tests,
all cylinders came out fine. Pressure test of cooling system came out
fine. I had a heater core replaced right before this started happening,
but I can't directly place the start of the problems with that.

So.... I am theorizing that as the engine cools it is sucking in air
into the cooling system. This leak is small enough that coolant is
leaking out but air is leaking in. Or... I have a bad heater core that
possibly is keeping air trapped in it, even when I bleed the system.

Any thoughts or similar experiences out there?

-Kurt

 

You sure could be describing a fan clutch on it's last legs....

To test it, heat the engine up fully, open the hood and have someone
shut off the engine while you watch the fan. If the fan clutch is good,
the fan will stop instantly. If the fan keep spinning, the clutch is
toast.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

"Kurt C. Hack" wrote:
>
> I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> system. Here is the scenario that I have played out about 5 times now,
> with replacing a myriad of parts, and the emptying of my wallet!
>
> 1. Lift rear of vehicle by driving up on ramps.
>
> 2. Fill system reservoir with 50/50 mix leaving cap off.
>
> 3. Unthread temp sending unit from to allow air to escape system. I
> continue this until only coolant comes out of the threads. I make sure
> to maintain coolant in the reservoir during this process.
>
> 4. Tighten up temp sending unit.
>
> 5. Make sure reservoir is filled up to about the halfway mark (the
> molding line) and screw cap back on tightly.
>
> 6. Start up engine and bring up to operating temperature.
>
> 7. Cooling system works great and holds temp at about 180F. I drive it
> around hard trying to get it to run hot, never moves above 185F.
>
> 8. Take it home and declare problem fixed and park the vehicle.
>
> 9. Next day start it up and drive it and bring it up to "normal"
> operating temp but notice that it is now 200F and when I come to a stop
> the temp starts creeping to 220F, but drops again when I start driving.
>
> 10. Take it home and park it and hear hissing from the reservoir. I let
> it cool down completely, assuming that I possibly had too much coolant
> in the system and it is just purging itself.
>
> 11. Start it up the next day and it start running even hotter and
> completely overheats whenever I come to a stop. I check the reservoir,
> and lo and behold, I have air in the system again and it has forced my
> coolant back out through the reservoir cap.
>
> 12. Go back to step 1. Grrrr....
>
> I have replaced the following to no avail, but my mechanic loves me!
>
> Radiator - Assumption was a blocked rad, which was actually correct but
> not the source of the problem!
>
> Temperature Sending Unit - Old one was acting erratically according to
> mechanic. I never had a problem with it, but he showed me the
> multimeter readings...
>
> Thermostat - Actually three of them now, just to be sure.
>
> Thermostat Housing - Apparently, all of those thermostat changes cracked
> the housing.
>
> Reservoir Cap - Could it be THAT easy?!??! Of course not.
>
> Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> prove it!
>
> They have also checked the head gasket by performing compression tests,
> all cylinders came out fine. Pressure test of cooling system came out
> fine. I had a heater core replaced right before this started happening,
> but I can't directly place the start of the problems with that.
>
> So.... I am theorizing that as the engine cools it is sucking in air
> into the cooling system. This leak is small enough that coolant is
> leaking out but air is leaking in. Or... I have a bad heater core that
> possibly is keeping air trapped in it, even when I bleed the system.
>
> Any thoughts or similar experiences out there?
>
> -Kurt

 

You sure could be describing a fan clutch on it's last legs....

To test it, heat the engine up fully, open the hood and have someone
shut off the engine while you watch the fan. If the fan clutch is good,
the fan will stop instantly. If the fan keep spinning, the clutch is
toast.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

"Kurt C. Hack" wrote:
>
> I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> system. Here is the scenario that I have played out about 5 times now,
> with replacing a myriad of parts, and the emptying of my wallet!
>
> 1. Lift rear of vehicle by driving up on ramps.
>
> 2. Fill system reservoir with 50/50 mix leaving cap off.
>
> 3. Unthread temp sending unit from to allow air to escape system. I
> continue this until only coolant comes out of the threads. I make sure
> to maintain coolant in the reservoir during this process.
>
> 4. Tighten up temp sending unit.
>
> 5. Make sure reservoir is filled up to about the halfway mark (the
> molding line) and screw cap back on tightly.
>
> 6. Start up engine and bring up to operating temperature.
>
> 7. Cooling system works great and holds temp at about 180F. I drive it
> around hard trying to get it to run hot, never moves above 185F.
>
> 8. Take it home and declare problem fixed and park the vehicle.
>
> 9. Next day start it up and drive it and bring it up to "normal"
> operating temp but notice that it is now 200F and when I come to a stop
> the temp starts creeping to 220F, but drops again when I start driving.
>
> 10. Take it home and park it and hear hissing from the reservoir. I let
> it cool down completely, assuming that I possibly had too much coolant
> in the system and it is just purging itself.
>
> 11. Start it up the next day and it start running even hotter and
> completely overheats whenever I come to a stop. I check the reservoir,
> and lo and behold, I have air in the system again and it has forced my
> coolant back out through the reservoir cap.
>
> 12. Go back to step 1. Grrrr....
>
> I have replaced the following to no avail, but my mechanic loves me!
>
> Radiator - Assumption was a blocked rad, which was actually correct but
> not the source of the problem!
>
> Temperature Sending Unit - Old one was acting erratically according to
> mechanic. I never had a problem with it, but he showed me the
> multimeter readings...
>
> Thermostat - Actually three of them now, just to be sure.
>
> Thermostat Housing - Apparently, all of those thermostat changes cracked
> the housing.
>
> Reservoir Cap - Could it be THAT easy?!??! Of course not.
>
> Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> prove it!
>
> They have also checked the head gasket by performing compression tests,
> all cylinders came out fine. Pressure test of cooling system came out
> fine. I had a heater core replaced right before this started happening,
> but I can't directly place the start of the problems with that.
>
> So.... I am theorizing that as the engine cools it is sucking in air
> into the cooling system. This leak is small enough that coolant is
> leaking out but air is leaking in. Or... I have a bad heater core that
> possibly is keeping air trapped in it, even when I bleed the system.
>
> Any thoughts or similar experiences out there?
>
> -Kurt

 

You sure could be describing a fan clutch on it's last legs....

To test it, heat the engine up fully, open the hood and have someone
shut off the engine while you watch the fan. If the fan clutch is good,
the fan will stop instantly. If the fan keep spinning, the clutch is
toast.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

"Kurt C. Hack" wrote:
>
> I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> system. Here is the scenario that I have played out about 5 times now,
> with replacing a myriad of parts, and the emptying of my wallet!
>
> 1. Lift rear of vehicle by driving up on ramps.
>
> 2. Fill system reservoir with 50/50 mix leaving cap off.
>
> 3. Unthread temp sending unit from to allow air to escape system. I
> continue this until only coolant comes out of the threads. I make sure
> to maintain coolant in the reservoir during this process.
>
> 4. Tighten up temp sending unit.
>
> 5. Make sure reservoir is filled up to about the halfway mark (the
> molding line) and screw cap back on tightly.
>
> 6. Start up engine and bring up to operating temperature.
>
> 7. Cooling system works great and holds temp at about 180F. I drive it
> around hard trying to get it to run hot, never moves above 185F.
>
> 8. Take it home and declare problem fixed and park the vehicle.
>
> 9. Next day start it up and drive it and bring it up to "normal"
> operating temp but notice that it is now 200F and when I come to a stop
> the temp starts creeping to 220F, but drops again when I start driving.
>
> 10. Take it home and park it and hear hissing from the reservoir. I let
> it cool down completely, assuming that I possibly had too much coolant
> in the system and it is just purging itself.
>
> 11. Start it up the next day and it start running even hotter and
> completely overheats whenever I come to a stop. I check the reservoir,
> and lo and behold, I have air in the system again and it has forced my
> coolant back out through the reservoir cap.
>
> 12. Go back to step 1. Grrrr....
>
> I have replaced the following to no avail, but my mechanic loves me!
>
> Radiator - Assumption was a blocked rad, which was actually correct but
> not the source of the problem!
>
> Temperature Sending Unit - Old one was acting erratically according to
> mechanic. I never had a problem with it, but he showed me the
> multimeter readings...
>
> Thermostat - Actually three of them now, just to be sure.
>
> Thermostat Housing - Apparently, all of those thermostat changes cracked
> the housing.
>
> Reservoir Cap - Could it be THAT easy?!??! Of course not.
>
> Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> prove it!
>
> They have also checked the head gasket by performing compression tests,
> all cylinders came out fine. Pressure test of cooling system came out
> fine. I had a heater core replaced right before this started happening,
> but I can't directly place the start of the problems with that.
>
> So.... I am theorizing that as the engine cools it is sucking in air
> into the cooling system. This leak is small enough that coolant is
> leaking out but air is leaking in. Or... I have a bad heater core that
> possibly is keeping air trapped in it, even when I bleed the system.
>
> Any thoughts or similar experiences out there?
>
> -Kurt

 

Forgive my ignorance, but how does the fan clutch introduce air into the
cooling system?

-Kurt

Mike Romain wrote:

> You sure could be describing a fan clutch on it's last legs....
>
> To test it, heat the engine up fully, open the hood and have someone
> shut off the engine while you watch the fan. If the fan clutch is good,
> the fan will stop instantly. If the fan keep spinning, the clutch is
> toast.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> "Kurt C. Hack" wrote:
>
>>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
>>system. Here is the scenario that I have played out about 5 times now,
>>with replacing a myriad of parts, and the emptying of my wallet!
>>
>>1. Lift rear of vehicle by driving up on ramps.
>>
>>2. Fill system reservoir with 50/50 mix leaving cap off.
>>
>>3. Unthread temp sending unit from to allow air to escape system. I
>>continue this until only coolant comes out of the threads. I make sure
>>to maintain coolant in the reservoir during this process.
>>
>>4. Tighten up temp sending unit.
>>
>>5. Make sure reservoir is filled up to about the halfway mark (the
>>molding line) and screw cap back on tightly.
>>
>>6. Start up engine and bring up to operating temperature.
>>
>>7. Cooling system works great and holds temp at about 180F. I drive it
>>around hard trying to get it to run hot, never moves above 185F.
>>
>>8. Take it home and declare problem fixed and park the vehicle.
>>
>>9. Next day start it up and drive it and bring it up to "normal"
>>operating temp but notice that it is now 200F and when I come to a stop
>>the temp starts creeping to 220F, but drops again when I start driving.
>>
>>10. Take it home and park it and hear hissing from the reservoir. I let
>>it cool down completely, assuming that I possibly had too much coolant
>>in the system and it is just purging itself.
>>
>>11. Start it up the next day and it start running even hotter and
>>completely overheats whenever I come to a stop. I check the reservoir,
>>and lo and behold, I have air in the system again and it has forced my
>>coolant back out through the reservoir cap.
>>
>>12. Go back to step 1. Grrrr....
>>
>>I have replaced the following to no avail, but my mechanic loves me!
>>
>>Radiator - Assumption was a blocked rad, which was actually correct but
>>not the source of the problem!
>>
>>Temperature Sending Unit - Old one was acting erratically according to
>>mechanic. I never had a problem with it, but he showed me the
>>multimeter readings...
>>
>>Thermostat - Actually three of them now, just to be sure.
>>
>>Thermostat Housing - Apparently, all of those thermostat changes cracked
>>the housing.
>>
>>Reservoir Cap - Could it be THAT easy?!??! Of course not.
>>
>>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
>>prove it!
>>
>>They have also checked the head gasket by performing compression tests,
>>all cylinders came out fine. Pressure test of cooling system came out
>>fine. I had a heater core replaced right before this started happening,
>>but I can't directly place the start of the problems with that.
>>
>>So.... I am theorizing that as the engine cools it is sucking in air
>>into the cooling system. This leak is small enough that coolant is
>>leaking out but air is leaking in. Or... I have a bad heater core that
>>possibly is keeping air trapped in it, even when I bleed the system.
>>
>>Any thoughts or similar experiences out there?
>>
>>-Kurt

 

Forgive my ignorance, but how does the fan clutch introduce air into the
cooling system?

-Kurt

Mike Romain wrote:

> You sure could be describing a fan clutch on it's last legs....
>
> To test it, heat the engine up fully, open the hood and have someone
> shut off the engine while you watch the fan. If the fan clutch is good,
> the fan will stop instantly. If the fan keep spinning, the clutch is
> toast.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> "Kurt C. Hack" wrote:
>
>>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
>>system. Here is the scenario that I have played out about 5 times now,
>>with replacing a myriad of parts, and the emptying of my wallet!
>>
>>1. Lift rear of vehicle by driving up on ramps.
>>
>>2. Fill system reservoir with 50/50 mix leaving cap off.
>>
>>3. Unthread temp sending unit from to allow air to escape system. I
>>continue this until only coolant comes out of the threads. I make sure
>>to maintain coolant in the reservoir during this process.
>>
>>4. Tighten up temp sending unit.
>>
>>5. Make sure reservoir is filled up to about the halfway mark (the
>>molding line) and screw cap back on tightly.
>>
>>6. Start up engine and bring up to operating temperature.
>>
>>7. Cooling system works great and holds temp at about 180F. I drive it
>>around hard trying to get it to run hot, never moves above 185F.
>>
>>8. Take it home and declare problem fixed and park the vehicle.
>>
>>9. Next day start it up and drive it and bring it up to "normal"
>>operating temp but notice that it is now 200F and when I come to a stop
>>the temp starts creeping to 220F, but drops again when I start driving.
>>
>>10. Take it home and park it and hear hissing from the reservoir. I let
>>it cool down completely, assuming that I possibly had too much coolant
>>in the system and it is just purging itself.
>>
>>11. Start it up the next day and it start running even hotter and
>>completely overheats whenever I come to a stop. I check the reservoir,
>>and lo and behold, I have air in the system again and it has forced my
>>coolant back out through the reservoir cap.
>>
>>12. Go back to step 1. Grrrr....
>>
>>I have replaced the following to no avail, but my mechanic loves me!
>>
>>Radiator - Assumption was a blocked rad, which was actually correct but
>>not the source of the problem!
>>
>>Temperature Sending Unit - Old one was acting erratically according to
>>mechanic. I never had a problem with it, but he showed me the
>>multimeter readings...
>>
>>Thermostat - Actually three of them now, just to be sure.
>>
>>Thermostat Housing - Apparently, all of those thermostat changes cracked
>>the housing.
>>
>>Reservoir Cap - Could it be THAT easy?!??! Of course not.
>>
>>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
>>prove it!
>>
>>They have also checked the head gasket by performing compression tests,
>>all cylinders came out fine. Pressure test of cooling system came out
>>fine. I had a heater core replaced right before this started happening,
>>but I can't directly place the start of the problems with that.
>>
>>So.... I am theorizing that as the engine cools it is sucking in air
>>into the cooling system. This leak is small enough that coolant is
>>leaking out but air is leaking in. Or... I have a bad heater core that
>>possibly is keeping air trapped in it, even when I bleed the system.
>>
>>Any thoughts or similar experiences out there?
>>
>>-Kurt

 

Forgive my ignorance, but how does the fan clutch introduce air into the
cooling system?

-Kurt

Mike Romain wrote:

> You sure could be describing a fan clutch on it's last legs....
>
> To test it, heat the engine up fully, open the hood and have someone
> shut off the engine while you watch the fan. If the fan clutch is good,
> the fan will stop instantly. If the fan keep spinning, the clutch is
> toast.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> "Kurt C. Hack" wrote:
>
>>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
>>system. Here is the scenario that I have played out about 5 times now,
>>with replacing a myriad of parts, and the emptying of my wallet!
>>
>>1. Lift rear of vehicle by driving up on ramps.
>>
>>2. Fill system reservoir with 50/50 mix leaving cap off.
>>
>>3. Unthread temp sending unit from to allow air to escape system. I
>>continue this until only coolant comes out of the threads. I make sure
>>to maintain coolant in the reservoir during this process.
>>
>>4. Tighten up temp sending unit.
>>
>>5. Make sure reservoir is filled up to about the halfway mark (the
>>molding line) and screw cap back on tightly.
>>
>>6. Start up engine and bring up to operating temperature.
>>
>>7. Cooling system works great and holds temp at about 180F. I drive it
>>around hard trying to get it to run hot, never moves above 185F.
>>
>>8. Take it home and declare problem fixed and park the vehicle.
>>
>>9. Next day start it up and drive it and bring it up to "normal"
>>operating temp but notice that it is now 200F and when I come to a stop
>>the temp starts creeping to 220F, but drops again when I start driving.
>>
>>10. Take it home and park it and hear hissing from the reservoir. I let
>>it cool down completely, assuming that I possibly had too much coolant
>>in the system and it is just purging itself.
>>
>>11. Start it up the next day and it start running even hotter and
>>completely overheats whenever I come to a stop. I check the reservoir,
>>and lo and behold, I have air in the system again and it has forced my
>>coolant back out through the reservoir cap.
>>
>>12. Go back to step 1. Grrrr....
>>
>>I have replaced the following to no avail, but my mechanic loves me!
>>
>>Radiator - Assumption was a blocked rad, which was actually correct but
>>not the source of the problem!
>>
>>Temperature Sending Unit - Old one was acting erratically according to
>>mechanic. I never had a problem with it, but he showed me the
>>multimeter readings...
>>
>>Thermostat - Actually three of them now, just to be sure.
>>
>>Thermostat Housing - Apparently, all of those thermostat changes cracked
>>the housing.
>>
>>Reservoir Cap - Could it be THAT easy?!??! Of course not.
>>
>>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
>>prove it!
>>
>>They have also checked the head gasket by performing compression tests,
>>all cylinders came out fine. Pressure test of cooling system came out
>>fine. I had a heater core replaced right before this started happening,
>>but I can't directly place the start of the problems with that.
>>
>>So.... I am theorizing that as the engine cools it is sucking in air
>>into the cooling system. This leak is small enough that coolant is
>>leaking out but air is leaking in. Or... I have a bad heater core that
>>possibly is keeping air trapped in it, even when I bleed the system.
>>
>>Any thoughts or similar experiences out there?
>>
>>-Kurt

 

It overheats it and spits it out, then it sucks air back in.

A 'hot spot' can just up and create air too like when it boils over.

If you run her hard and at speed, there is enough air flow from moving
to keep the engine cool. If the clutch is bad, it messes up most in
stop and go traffic and at speeds below 30 mph.

The system will start making burping noises just before it blows over.
The burps are hot spots boiling.

Mike

"Kurt C. Hack" wrote:
>
> Forgive my ignorance, but how does the fan clutch introduce air into the
> cooling system?
>
> -Kurt
>
> Mike Romain wrote:
>
> > You sure could be describing a fan clutch on it's last legs....
> >
> > To test it, heat the engine up fully, open the hood and have someone
> > shut off the engine while you watch the fan. If the fan clutch is good,
> > the fan will stop instantly. If the fan keep spinning, the clutch is
> > toast.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > "Kurt C. Hack" wrote:
> >
> >>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> >>system. Here is the scenario that I have played out about 5 times now,
> >>with replacing a myriad of parts, and the emptying of my wallet!
> >>
> >>1. Lift rear of vehicle by driving up on ramps.
> >>
> >>2. Fill system reservoir with 50/50 mix leaving cap off.
> >>
> >>3. Unthread temp sending unit from to allow air to escape system. I
> >>continue this until only coolant comes out of the threads. I make sure
> >>to maintain coolant in the reservoir during this process.
> >>
> >>4. Tighten up temp sending unit.
> >>
> >>5. Make sure reservoir is filled up to about the halfway mark (the
> >>molding line) and screw cap back on tightly.
> >>
> >>6. Start up engine and bring up to operating temperature.
> >>
> >>7. Cooling system works great and holds temp at about 180F. I drive it
> >>around hard trying to get it to run hot, never moves above 185F.
> >>
> >>8. Take it home and declare problem fixed and park the vehicle.
> >>
> >>9. Next day start it up and drive it and bring it up to "normal"
> >>operating temp but notice that it is now 200F and when I come to a stop
> >>the temp starts creeping to 220F, but drops again when I start driving.
> >>
> >>10. Take it home and park it and hear hissing from the reservoir. I let
> >>it cool down completely, assuming that I possibly had too much coolant
> >>in the system and it is just purging itself.
> >>
> >>11. Start it up the next day and it start running even hotter and
> >>completely overheats whenever I come to a stop. I check the reservoir,
> >>and lo and behold, I have air in the system again and it has forced my
> >>coolant back out through the reservoir cap.
> >>
> >>12. Go back to step 1. Grrrr....
> >>
> >>I have replaced the following to no avail, but my mechanic loves me!
> >>
> >>Radiator - Assumption was a blocked rad, which was actually correct but
> >>not the source of the problem!
> >>
> >>Temperature Sending Unit - Old one was acting erratically according to
> >>mechanic. I never had a problem with it, but he showed me the
> >>multimeter readings...
> >>
> >>Thermostat - Actually three of them now, just to be sure.
> >>
> >>Thermostat Housing - Apparently, all of those thermostat changes cracked
> >>the housing.
> >>
> >>Reservoir Cap - Could it be THAT easy?!??! Of course not.
> >>
> >>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> >>prove it!
> >>
> >>They have also checked the head gasket by performing compression tests,
> >>all cylinders came out fine. Pressure test of cooling system came out
> >>fine. I had a heater core replaced right before this started happening,
> >>but I can't directly place the start of the problems with that.
> >>
> >>So.... I am theorizing that as the engine cools it is sucking in air
> >>into the cooling system. This leak is small enough that coolant is
> >>leaking out but air is leaking in. Or... I have a bad heater core that
> >>possibly is keeping air trapped in it, even when I bleed the system.
> >>
> >>Any thoughts or similar experiences out there?
> >>
> >>-Kurt

 

It overheats it and spits it out, then it sucks air back in.

A 'hot spot' can just up and create air too like when it boils over.

If you run her hard and at speed, there is enough air flow from moving
to keep the engine cool. If the clutch is bad, it messes up most in
stop and go traffic and at speeds below 30 mph.

The system will start making burping noises just before it blows over.
The burps are hot spots boiling.

Mike

"Kurt C. Hack" wrote:
>
> Forgive my ignorance, but how does the fan clutch introduce air into the
> cooling system?
>
> -Kurt
>
> Mike Romain wrote:
>
> > You sure could be describing a fan clutch on it's last legs....
> >
> > To test it, heat the engine up fully, open the hood and have someone
> > shut off the engine while you watch the fan. If the fan clutch is good,
> > the fan will stop instantly. If the fan keep spinning, the clutch is
> > toast.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > "Kurt C. Hack" wrote:
> >
> >>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> >>system. Here is the scenario that I have played out about 5 times now,
> >>with replacing a myriad of parts, and the emptying of my wallet!
> >>
> >>1. Lift rear of vehicle by driving up on ramps.
> >>
> >>2. Fill system reservoir with 50/50 mix leaving cap off.
> >>
> >>3. Unthread temp sending unit from to allow air to escape system. I
> >>continue this until only coolant comes out of the threads. I make sure
> >>to maintain coolant in the reservoir during this process.
> >>
> >>4. Tighten up temp sending unit.
> >>
> >>5. Make sure reservoir is filled up to about the halfway mark (the
> >>molding line) and screw cap back on tightly.
> >>
> >>6. Start up engine and bring up to operating temperature.
> >>
> >>7. Cooling system works great and holds temp at about 180F. I drive it
> >>around hard trying to get it to run hot, never moves above 185F.
> >>
> >>8. Take it home and declare problem fixed and park the vehicle.
> >>
> >>9. Next day start it up and drive it and bring it up to "normal"
> >>operating temp but notice that it is now 200F and when I come to a stop
> >>the temp starts creeping to 220F, but drops again when I start driving.
> >>
> >>10. Take it home and park it and hear hissing from the reservoir. I let
> >>it cool down completely, assuming that I possibly had too much coolant
> >>in the system and it is just purging itself.
> >>
> >>11. Start it up the next day and it start running even hotter and
> >>completely overheats whenever I come to a stop. I check the reservoir,
> >>and lo and behold, I have air in the system again and it has forced my
> >>coolant back out through the reservoir cap.
> >>
> >>12. Go back to step 1. Grrrr....
> >>
> >>I have replaced the following to no avail, but my mechanic loves me!
> >>
> >>Radiator - Assumption was a blocked rad, which was actually correct but
> >>not the source of the problem!
> >>
> >>Temperature Sending Unit - Old one was acting erratically according to
> >>mechanic. I never had a problem with it, but he showed me the
> >>multimeter readings...
> >>
> >>Thermostat - Actually three of them now, just to be sure.
> >>
> >>Thermostat Housing - Apparently, all of those thermostat changes cracked
> >>the housing.
> >>
> >>Reservoir Cap - Could it be THAT easy?!??! Of course not.
> >>
> >>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> >>prove it!
> >>
> >>They have also checked the head gasket by performing compression tests,
> >>all cylinders came out fine. Pressure test of cooling system came out
> >>fine. I had a heater core replaced right before this started happening,
> >>but I can't directly place the start of the problems with that.
> >>
> >>So.... I am theorizing that as the engine cools it is sucking in air
> >>into the cooling system. This leak is small enough that coolant is
> >>leaking out but air is leaking in. Or... I have a bad heater core that
> >>possibly is keeping air trapped in it, even when I bleed the system.
> >>
> >>Any thoughts or similar experiences out there?
> >>
> >>-Kurt

 

It overheats it and spits it out, then it sucks air back in.

A 'hot spot' can just up and create air too like when it boils over.

If you run her hard and at speed, there is enough air flow from moving
to keep the engine cool. If the clutch is bad, it messes up most in
stop and go traffic and at speeds below 30 mph.

The system will start making burping noises just before it blows over.
The burps are hot spots boiling.

Mike

"Kurt C. Hack" wrote:
>
> Forgive my ignorance, but how does the fan clutch introduce air into the
> cooling system?
>
> -Kurt
>
> Mike Romain wrote:
>
> > You sure could be describing a fan clutch on it's last legs....
> >
> > To test it, heat the engine up fully, open the hood and have someone
> > shut off the engine while you watch the fan. If the fan clutch is good,
> > the fan will stop instantly. If the fan keep spinning, the clutch is
> > toast.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > "Kurt C. Hack" wrote:
> >
> >>I have an 87 XJ 4.0L that appears to be getting air into the closed loop
> >>system. Here is the scenario that I have played out about 5 times now,
> >>with replacing a myriad of parts, and the emptying of my wallet!
> >>
> >>1. Lift rear of vehicle by driving up on ramps.
> >>
> >>2. Fill system reservoir with 50/50 mix leaving cap off.
> >>
> >>3. Unthread temp sending unit from to allow air to escape system. I
> >>continue this until only coolant comes out of the threads. I make sure
> >>to maintain coolant in the reservoir during this process.
> >>
> >>4. Tighten up temp sending unit.
> >>
> >>5. Make sure reservoir is filled up to about the halfway mark (the
> >>molding line) and screw cap back on tightly.
> >>
> >>6. Start up engine and bring up to operating temperature.
> >>
> >>7. Cooling system works great and holds temp at about 180F. I drive it
> >>around hard trying to get it to run hot, never moves above 185F.
> >>
> >>8. Take it home and declare problem fixed and park the vehicle.
> >>
> >>9. Next day start it up and drive it and bring it up to "normal"
> >>operating temp but notice that it is now 200F and when I come to a stop
> >>the temp starts creeping to 220F, but drops again when I start driving.
> >>
> >>10. Take it home and park it and hear hissing from the reservoir. I let
> >>it cool down completely, assuming that I possibly had too much coolant
> >>in the system and it is just purging itself.
> >>
> >>11. Start it up the next day and it start running even hotter and
> >>completely overheats whenever I come to a stop. I check the reservoir,
> >>and lo and behold, I have air in the system again and it has forced my
> >>coolant back out through the reservoir cap.
> >>
> >>12. Go back to step 1. Grrrr....
> >>
> >>I have replaced the following to no avail, but my mechanic loves me!
> >>
> >>Radiator - Assumption was a blocked rad, which was actually correct but
> >>not the source of the problem!
> >>
> >>Temperature Sending Unit - Old one was acting erratically according to
> >>mechanic. I never had a problem with it, but he showed me the
> >>multimeter readings...
> >>
> >>Thermostat - Actually three of them now, just to be sure.
> >>
> >>Thermostat Housing - Apparently, all of those thermostat changes cracked
> >>the housing.
> >>
> >>Reservoir Cap - Could it be THAT easy?!??! Of course not.
> >>
> >>Fan Shroud - Old one was broken, I have the chuck out of my knuckles to
> >>prove it!
> >>
> >>They have also checked the head gasket by performing compression tests,
> >>all cylinders came out fine. Pressure test of cooling system came out
> >>fine. I had a heater core replaced right before this started happening,
> >>but I can't directly place the start of the problems with that.
> >>
> >>So.... I am theorizing that as the engine cools it is sucking in air
> >>into the cooling system. This leak is small enough that coolant is
> >>leaking out but air is leaking in. Or... I have a bad heater core that
> >>possibly is keeping air trapped in it, even when I bleed the system.
> >>
> >>Any thoughts or similar experiences out there?
> >>
> >>-Kurt