These gauges are usually of the bimetallic strip type. There is a mini
voltage regulator somewhere in the dash panel, that feeds them the correct
voltage. Ones I have seen look a little like a shrunken turn signal
flasher. The regulator itself could be the culprit, or it could be bad
voltage or ground to the instrument panel.

Saludos,

Earle

"jerryg" <Gregginn7@msn.com> wrote in message
news:1167186529.119005.197240@f1g2000cwa.googlegro ups.com...
> Hey Dan, It does'nt run up to a hot temp and stay there, the gauge goes
> up and down, constantly. I don't know how the fluid can change temp
> like that so abruptly, that is if the new sending unit is working
> properly.
>
> Thanks,
> Greg
> Hootowl wrote:
> > On 26 Dec 2006 17:00:54 -0800, "jerryg" <Gregginn7@msn.com> wrote:
> >
> > >Good evening all. I have appeared here before with a erratic temp
> > >gauge. After confirming that the engine block is not plugged, having a
> > >new correct flow water pump installed, a recent radiator, new
> > >thermostat, twice this week, and this evening a new temp sending unit,
> > >my gauge still will not sit at 210. The old sending unit was corroded,
> > >and fell apart when I removed it. I knew it was bad. The gauge used to
> > >flucuate between 210 and 260. Up and down constantly. Now it goes up
> > >and down between 210 and 235. When I first start it and let it warm up,
> > >it hangs around 210, and when I start driving, it begins to move. Why.
> > >
> > What model is it? I had a similar problem on my '77 Cherokee (195
> > degree thermostat). In town, summer or winter, A/C or not, gauge read
> > at the lower end of the green zone (195 or so). At higher speeds, it
> > would run higher. In summer, with the A/C on and driving on the
> > freeway, it would run near the end of the green range (but not
> > actually overheat). It didn't used to get that hot unless I was
> > towing down a crowded highway in hot midday sun. I replaced the
> > radiator with an identical Modine (stock), when the old one finally
> > quit. Same song, second verse. When that one quit last summer, I did
> > the obvious fix-a radiator with one more row of tubes (from three rows
> > to four-doubles cooling capacity-it's a direct square relationship).
> > Still runs hotter at high speed (the engine has to work harder), but
> > only slightly. Problem solved, and -DUH- it finally dawned on me-it
> > was made for the then national speed limit of 55 mph (and the radiator
> > size was not increased when full-time-four-wheel-drive (Quadratrac)
> > was introduced back in the '70's (it has no two-wheel-drive capability
> > at all). At 65-70+, ram air is no longer sufficient for the extra
> > load placed on any engine, and more cooling is required. But I do now
> > have a piece of cardboard covering about half the radiator during cold
> > weather to help it heat up better. Especially since it's only a
> > 6-minute drive to work. An oversized radiator would definitely hold
> > your temperature down. Hope this helps.
> >
> > Dan
> >
> >
> > >Thanks,
> > >
> > >Greg
>

 

These gauges are usually of the bimetallic strip type. There is a mini
voltage regulator somewhere in the dash panel, that feeds them the correct
voltage. Ones I have seen look a little like a shrunken turn signal
flasher. The regulator itself could be the culprit, or it could be bad
voltage or ground to the instrument panel.

Saludos,

Earle

"jerryg" <Gregginn7@msn.com> wrote in message
news:1167186529.119005.197240@f1g2000cwa.googlegro ups.com...
> Hey Dan, It does'nt run up to a hot temp and stay there, the gauge goes
> up and down, constantly. I don't know how the fluid can change temp
> like that so abruptly, that is if the new sending unit is working
> properly.
>
> Thanks,
> Greg
> Hootowl wrote:
> > On 26 Dec 2006 17:00:54 -0800, "jerryg" <Gregginn7@msn.com> wrote:
> >
> > >Good evening all. I have appeared here before with a erratic temp
> > >gauge. After confirming that the engine block is not plugged, having a
> > >new correct flow water pump installed, a recent radiator, new
> > >thermostat, twice this week, and this evening a new temp sending unit,
> > >my gauge still will not sit at 210. The old sending unit was corroded,
> > >and fell apart when I removed it. I knew it was bad. The gauge used to
> > >flucuate between 210 and 260. Up and down constantly. Now it goes up
> > >and down between 210 and 235. When I first start it and let it warm up,
> > >it hangs around 210, and when I start driving, it begins to move. Why.
> > >
> > What model is it? I had a similar problem on my '77 Cherokee (195
> > degree thermostat). In town, summer or winter, A/C or not, gauge read
> > at the lower end of the green zone (195 or so). At higher speeds, it
> > would run higher. In summer, with the A/C on and driving on the
> > freeway, it would run near the end of the green range (but not
> > actually overheat). It didn't used to get that hot unless I was
> > towing down a crowded highway in hot midday sun. I replaced the
> > radiator with an identical Modine (stock), when the old one finally
> > quit. Same song, second verse. When that one quit last summer, I did
> > the obvious fix-a radiator with one more row of tubes (from three rows
> > to four-doubles cooling capacity-it's a direct square relationship).
> > Still runs hotter at high speed (the engine has to work harder), but
> > only slightly. Problem solved, and -DUH- it finally dawned on me-it
> > was made for the then national speed limit of 55 mph (and the radiator
> > size was not increased when full-time-four-wheel-drive (Quadratrac)
> > was introduced back in the '70's (it has no two-wheel-drive capability
> > at all). At 65-70+, ram air is no longer sufficient for the extra
> > load placed on any engine, and more cooling is required. But I do now
> > have a piece of cardboard covering about half the radiator during cold
> > weather to help it heat up better. Especially since it's only a
> > 6-minute drive to work. An oversized radiator would definitely hold
> > your temperature down. Hope this helps.
> >
> > Dan
> >
> >
> > >Thanks,
> > >
> > >Greg
>

 

On 26 Dec 2006 18:28:49 -0800, "jerryg" <Gregginn7@msn.com> wrote:

>Hey Dan, It does'nt run up to a hot temp and stay there, the gauge goes
>up and down, constantly. I don't know how the fluid can change temp
>like that so abruptly, that is if the new sending unit is working
>properly.

It can't, unless the thermostat is having an odd sticking problem
(possible). Actually, that's a more likely cause than the sending
unit. It would go something like this (I once had thermostat that
would stick, then suddenly open and work properly until the next cold
start, on a '65 Scout): The thermostat sticks causing the gauge to
rise, then suddenly springs open. The gauge now falls as the coolant
suddenly begins circulating through the radiator. Since it's cool
weather, the thermostat closes again and again sticks shut until it
gets hot enough to again break loose and pop open, beginning the cycle
again. Are you sure the thermostat was actually replaced? And, also,
are you sure the thermostat is not installed incorrectly, causing it
to warp slightly? Is the thermostat housing cover itself warped from
uneven bolt torque?

A defective sending unit, however isn't impossible. I once went
through 4 defective oil pressure sending units (not all from the same
parts house but all apparently all were from the same manufacturer)
and no two gave identical readings. Which makes me think-check for an
intermittent partial short to the block, frame, or body on the sending
unit wire itself. Grounding the sending unit lead will cause the oil
pressure gauge to peg out (harmlessly). As you've said nothing about
other gauges, I'm assuming they are performing normally. If they are
also involved, it could be the CVR (usually built into the temperature
gauge). On vehicles so equipped, it maintains a constant 3.6 volts
(or something like that) to all the gauges except the ammeter or
voltmeter.

Dan
>
>Thanks,
>Greg

 

On 26 Dec 2006 18:28:49 -0800, "jerryg" <Gregginn7@msn.com> wrote:

>Hey Dan, It does'nt run up to a hot temp and stay there, the gauge goes
>up and down, constantly. I don't know how the fluid can change temp
>like that so abruptly, that is if the new sending unit is working
>properly.

It can't, unless the thermostat is having an odd sticking problem
(possible). Actually, that's a more likely cause than the sending
unit. It would go something like this (I once had thermostat that
would stick, then suddenly open and work properly until the next cold
start, on a '65 Scout): The thermostat sticks causing the gauge to
rise, then suddenly springs open. The gauge now falls as the coolant
suddenly begins circulating through the radiator. Since it's cool
weather, the thermostat closes again and again sticks shut until it
gets hot enough to again break loose and pop open, beginning the cycle
again. Are you sure the thermostat was actually replaced? And, also,
are you sure the thermostat is not installed incorrectly, causing it
to warp slightly? Is the thermostat housing cover itself warped from
uneven bolt torque?

A defective sending unit, however isn't impossible. I once went
through 4 defective oil pressure sending units (not all from the same
parts house but all apparently all were from the same manufacturer)
and no two gave identical readings. Which makes me think-check for an
intermittent partial short to the block, frame, or body on the sending
unit wire itself. Grounding the sending unit lead will cause the oil
pressure gauge to peg out (harmlessly). As you've said nothing about
other gauges, I'm assuming they are performing normally. If they are
also involved, it could be the CVR (usually built into the temperature
gauge). On vehicles so equipped, it maintains a constant 3.6 volts
(or something like that) to all the gauges except the ammeter or
voltmeter.

Dan
>
>Thanks,
>Greg

 

On 26 Dec 2006 18:28:49 -0800, "jerryg" <Gregginn7@msn.com> wrote:

>Hey Dan, It does'nt run up to a hot temp and stay there, the gauge goes
>up and down, constantly. I don't know how the fluid can change temp
>like that so abruptly, that is if the new sending unit is working
>properly.

It can't, unless the thermostat is having an odd sticking problem
(possible). Actually, that's a more likely cause than the sending
unit. It would go something like this (I once had thermostat that
would stick, then suddenly open and work properly until the next cold
start, on a '65 Scout): The thermostat sticks causing the gauge to
rise, then suddenly springs open. The gauge now falls as the coolant
suddenly begins circulating through the radiator. Since it's cool
weather, the thermostat closes again and again sticks shut until it
gets hot enough to again break loose and pop open, beginning the cycle
again. Are you sure the thermostat was actually replaced? And, also,
are you sure the thermostat is not installed incorrectly, causing it
to warp slightly? Is the thermostat housing cover itself warped from
uneven bolt torque?

A defective sending unit, however isn't impossible. I once went
through 4 defective oil pressure sending units (not all from the same
parts house but all apparently all were from the same manufacturer)
and no two gave identical readings. Which makes me think-check for an
intermittent partial short to the block, frame, or body on the sending
unit wire itself. Grounding the sending unit lead will cause the oil
pressure gauge to peg out (harmlessly). As you've said nothing about
other gauges, I'm assuming they are performing normally. If they are
also involved, it could be the CVR (usually built into the temperature
gauge). On vehicles so equipped, it maintains a constant 3.6 volts
(or something like that) to all the gauges except the ammeter or
voltmeter.

Dan
>
>Thanks,
>Greg