Interesting..... I took a look and the fan does not stop 'immediately'
but it does stop within 1-2 seconds. Is this indicative of what you are
describing or should I be looking for in to continue running as though
it were free wheeling?

Thanks,
-Kurt

Mike Romain wrote:

> 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

 

Interesting..... I took a look and the fan does not stop 'immediately'
but it does stop within 1-2 seconds. Is this indicative of what you are
describing or should I be looking for in to continue running as though
it were free wheeling?

Thanks,
-Kurt

Mike Romain wrote:

> 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

 

Interesting..... I took a look and the fan does not stop 'immediately'
but it does stop within 1-2 seconds. Is this indicative of what you are
describing or should I be looking for in to continue running as though
it were free wheeling?

Thanks,
-Kurt

Mike Romain wrote:

> 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

 

On Sat, 28 Feb 2004 11:30:02 -0500, Mike Romain <romainm@sympatico.ca>
wrote:

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

The same could be said for many after monster burrito's at the taco pit.

But that is a different story all together....


--
Taylor

'89 Audi 200
'03 Audi S6 Avant
'98 Jeep Cherokee Sport

 

On Sat, 28 Feb 2004 11:30:02 -0500, Mike Romain <romainm@sympatico.ca>
wrote:

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

The same could be said for many after monster burrito's at the taco pit.

But that is a different story all together....


--
Taylor

'89 Audi 200
'03 Audi S6 Avant
'98 Jeep Cherokee Sport

 

On Sat, 28 Feb 2004 11:30:02 -0500, Mike Romain <romainm@sympatico.ca>
wrote:

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

The same could be said for many after monster burrito's at the taco pit.

But that is a different story all together....


--
Taylor

'89 Audi 200
'03 Audi S6 Avant
'98 Jeep Cherokee Sport

 

A hot fan clutch is in an almost seized up mode. This will stop the fan
almost instantly. My new one on my 88 will only move maybe one blade
width after a stop when hot.

Another test is to shut the engine off hot and grab the fan and give it
a hard push with 2 fingers. The next blade in line should not move far
enough to tag the back of your knuckles.

If it gets to a point of free wheeling, then it is about to go
ballistic. Literally, it will fly off and eat the shroud only if you
are lucky or take out the rad too. We were lucky and only lost the
shroud.. ;-)

Mike

"Kurt C. Hack" wrote:
>
> Interesting..... I took a look and the fan does not stop 'immediately'
> but it does stop within 1-2 seconds. Is this indicative of what you are
> describing or should I be looking for in to continue running as though
> it were free wheeling?
>
> Thanks,
> -Kurt
>
> Mike Romain wrote:
>
> > 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

 

A hot fan clutch is in an almost seized up mode. This will stop the fan
almost instantly. My new one on my 88 will only move maybe one blade
width after a stop when hot.

Another test is to shut the engine off hot and grab the fan and give it
a hard push with 2 fingers. The next blade in line should not move far
enough to tag the back of your knuckles.

If it gets to a point of free wheeling, then it is about to go
ballistic. Literally, it will fly off and eat the shroud only if you
are lucky or take out the rad too. We were lucky and only lost the
shroud.. ;-)

Mike

"Kurt C. Hack" wrote:
>
> Interesting..... I took a look and the fan does not stop 'immediately'
> but it does stop within 1-2 seconds. Is this indicative of what you are
> describing or should I be looking for in to continue running as though
> it were free wheeling?
>
> Thanks,
> -Kurt
>
> Mike Romain wrote:
>
> > 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

 

A hot fan clutch is in an almost seized up mode. This will stop the fan
almost instantly. My new one on my 88 will only move maybe one blade
width after a stop when hot.

Another test is to shut the engine off hot and grab the fan and give it
a hard push with 2 fingers. The next blade in line should not move far
enough to tag the back of your knuckles.

If it gets to a point of free wheeling, then it is about to go
ballistic. Literally, it will fly off and eat the shroud only if you
are lucky or take out the rad too. We were lucky and only lost the
shroud.. ;-)

Mike

"Kurt C. Hack" wrote:
>
> Interesting..... I took a look and the fan does not stop 'immediately'
> but it does stop within 1-2 seconds. Is this indicative of what you are
> describing or should I be looking for in to continue running as though
> it were free wheeling?
>
> Thanks,
> -Kurt
>
> Mike Romain wrote:
>
> > 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