temp gauge and heat problem, Related??

[chris82]

My thermostat went bad a while back. I replaced it and all was well. temp guage was fine and heat worked etc. never a problem. Months later, now, my temp guage in my dash will go eratic going up to H and then back down to normal etc. it will do this in the morning on the way to work when it is cold all the time. After a while it settles down in the middle and doesn't move. when it is a little warmer, like on my way home, it acts normal. I checked it with a code reader and my coolant temp was showing over 100* like 5 seconds after startup. this is obviously wrong on a cold engine. Not sure what that could be. My heat works with my temp gauge. when the truck is heating up or "running" hot according to the gauge, the heat is cold but when the temp starts coming back down it is hot. I let it run up to the H this morning because i'm sure the gauge is bad.....this yielded no issues with performance on the vehicle and i ran a systems check on my on board computer, said the engine temp was fine. if my truck was really running as hot as it said it was this morning then it would have run like crap, probably would have smelled it....but i had no symptoms at all. but this afternoon when i go home it might heat up once and then go right back to normal temp and stay there. doesn't make any sense at all. I have a feeling these two things are related but not sure where or how. any ideas? Is the sender to the gauge the same that goes to the computer and controls the heat? when i mean erratic, it will take a while to warm up, it will go to warm, then all the way back to cold and then to running temp. then it will start going up and then back to normal and keep doing this for at least 20 minutes and then it stays put in the middle like it should and my heat works.

 

[96eb96]

My thermostat went bad a while back. I replaced it and all was well. temp guage was fine and heat worked etc. never a problem. Months later, now, my temp guage in my dash will go eratic going up to H and then back down to normal etc. it will do this in the morning on the way to work when it is cold all the time. After a while it settles down in the middle and doesn't move. when it is a little warmer, like on my way home, it acts normal. I checked it with a code reader and my coolant temp was showing over 100* like 5 seconds after startup. this is obviously wrong on a cold engine. Not sure what that could be. My heat works with my temp gauge. when the truck is heating up or "running" hot according to the gauge, the heat is cold but when the temp starts coming back down it is hot. I let it run up to the H this morning because i'm sure the gauge is bad.....this yielded no issues with performance on the vehicle and i ran a systems check on my on board computer, said the engine temp was fine. if my truck was really running as hot as it said it was this morning then it would have run like crap, probably would have smelled it....but i had no symptoms at all. but this afternoon when i go home it might heat up once and then go right back to normal temp and stay there. doesn't make any sense at all. I have a feeling these two things are related but not sure where or how. any ideas? Is the sender to the gauge the same that goes to the computer and controls the heat? when i mean erratic, it will take a while to warm up, it will go to warm, then all the way back to cold and then to running temp. then it will start going up and then back to normal and keep doing this for at least 20 minutes and then it stays put in the middle like it should and my heat works.

Change your gauge temp SENDER above the thermostat. They go bad.

 

[gijoecam]

If you have a 4.0 SOHC, be VERY careful replacing the sensor and sending unit. The threaded inserts are molded into the thermostat housing and the housing is not available separately. It comes as an assembly for a whopping $250.

As for the problem, could be a thermostat, sensor, sending unit, or all three.

The gauge is connected to the sending unit. The ECU is connected to the sensor. If the gauge is reading off but the ECU temp sensor reads correct, replace the sending unit.

-Joe

 

[MustangP51]

IF your heat isn't working properly then I would say that the thermostat is bad. I would replace it as soon as possible, it could fail and not open and cook your engine.

 

[chris82]

the only issue i see is that the truck runs fine no matter what the gauge says. the on board computer says the temp is fine even when it is extremely hot. But when it is warmer outside i have no issues at all so that kind of rules out the thermostat. if it was the thermostat then the warmer weather would make it worse right?

 

[ken freeman]

It sounds like a classic case of the water level being too low. once the engine heats up and the water expands enough you get heat. i found my aerostar will run cool until it is very low on water.

 

[BurnTheLight88]

I second the low level idea. The temp will get hot because of the lack of fluid but the heat won't blow hot