Guage problem

[Herb]

One day I got into my 72 Jimmy and after it warmed up the temperature gauge went all the way into the red. I shut it down and after awhile I turned it on and the gauge was back to normal. I startred it up and headed back home, on the way it went into the red again. When I got it into the garage I shut it down and let it set for a few minutes. I put my hand on the radiator and it didn't even feel hot. I checked the coolant level, it was right where it was supposed to be so I stuck my finger into the coolant, unconfortable but not hot. I checked all of the hoses, no problem there. I replaced the original temperature sending unit, no change. I replaced the dash temperature gauge, no change. I took it to the local mechanic and had the entire system backflushed, no change. He replaced the 180 degree thermostat, no change. I drove it until it went into the red again and the mechanic used an infrared temperature indicator on the thermostat housing and it read 179 degrees but the gauge was in the red. The radiator is the original one and it was totally rebuilt about 3,000 miles ago. I'm at my wits end here, driving it with the temp gauge in the red really freaks me out even though I know the engine is not hot, but some day it might be for real and I'll get some serious engine damage. Any thoughts on what's wrong will be greatly appreciated, thanks, Herb. (all fuses have been checked too, no problems, and the coolant is the correct mixture)

[Torque Junkie]

It sounds like the wire to your temperature sensor has grounded out or the sensor itself has faulted internally.

 

My '79 did the same thing and come to find out the wire that goes to the sensor got stuck between the valve cover and A/C Compressor and then it melted, thus shorting out.

 

The sensor should be on the drivers side of the engine, towards the front, either in the head or the block (I cant remember)

 

Good luck!

 

-Mike

[Cool Zr2]

its in the head

[Herb]

The sending unit is in the left head (driver's side) tucked up under the exhaust manifold between number 1 and 3 cylinders. I've replaced that too and traced the green wire from the sending unit into the firewall and haven't found any breaks or bare spots.

[citydriver]

The gauge itself may have went bad...in the cluster..you may want to try a replacement from a donor vehicle...or you can buy a new replacement fromClassic Industries

[Colorado Kid]

You've been pretty thourough. About the only thing you haven't mentioned is the condition of the grounds. Check to see that engine ground strap is in good condition and solidly connected at both ends, and that the panel is well grounded.

 

If that fails to fix it there's always a mechanical temp guage.

[TomA]

You've been pretty thourough.  About the only thing you haven't mentioned is the condition of the grounds.  Check to see that engine ground strap is in good condition and solidly connected at both ends, and that the panel is well grounded.

 

If that fails to fix it  there's always a mechanical temp guage.

 

<{POST_SNAPBACK}>

 

 

 

I have been having the same problem with my '77. The sender is in the upper block on the passenger side towards the rear of engine. There is a plug on the drivers side near the front. I installed a mechanical gauge there. It stays at 180 degrees. Takes a load off my mind while I track down the problem.