Need some help with a fluctuating temp guage

[stafphoto1]

OK I've replaced everything I can think of trying to figure out this problem. I have a 1996 4.0 v6 explorer with a temp gauge that doesn't want to hold still. I've replaced the thermostate, the water pump, the fan clutch, the sensor that runs to the temp gauge and some of the radiator hoses. Also burped out the system.

The strangest thing about the problem though is that if I leave the heat off the gauge tends to stay a bit below halfway and doesn't really move. But if I turn the heat on after a minute the gauge will go up past half way then back close to the bottom line maybe sit for a minute and then keep doing it. The coolant level seems to be staying constant I don't see any leaks I smell no coolant and the oil is fine. Also not noticing any strange exhaust color.

I'm stumped as to what else to try does anyone have ideas I'd really like to get this fixed?

 

[stafphoto1]

I should also ad that the radiator is only about two months old as well.

 

[pbnj22]

does the actual temp change or is it just the "dummy gauge" that moves? can you hook up a machine to your obd2 port and see what the computer sees as the temp?

 

[koda2000]

your symptoms don't make sense. check the actual coolant temp and (stupid question) are you sure you installed the thermostat facing the right way?

 

[Bobmbx]

Use a volt meter and check the voltage at the temp sensor connector (engine running, temp sensor disconnected). Lets see if the voltage to the sensor is fluctuating.

If it doesn't fluctuate, then re-install the temp sensor cable and check the voltage again (engine running).

Also, are both radiator hoses getting hot?

 

[koda2000]

Use a volt meter and check the voltage at the temp sensor connector (engine running, temp sensor disconnected). Lets see if the voltage to the sensor is fluctuating.

If it doesn't fluctuate, then re-install the temp sensor cable and check the voltage again (engine running).

Also, are both radiator hoses getting hot?

as the temp gauge works on ohms resistance, I don't think you're going to see any voltage there, but the resistance should change with temp increase.

 

[Bobmbx]

as the temp gauge works on ohms resistance, I don't think you're going to see any voltage there, but the resistance should change with temp increase.

The first check is to monitor the power supply to the sensor. Resistors don't do anything without current at some voltage. I want to see if the power supply is not regulating to the sensor.

I suppose you could check the sensor terminals for resistance changes while the cable is disconnected.

I think he's either got a bad voltage regulator, or some serious coolant flow problems.

 

[stafphoto]

Ill check both hoses when I get home to make sure they are both hot. And yes Im pretty sure the thermostate is facing the proper direction I have the largest part of it I guess you could say facing into the engine itself. The only thing I'm not sure of is if I have the little hole thats in the ring of the thermostate facing up. But im not sure if that would cause the trouble or not?

Is it possible for some part of the heater to be pulling in air or to have air trapped in the heater core?

And yes its a strange issue. If I leave the heat turned off the guage stays pretty much at a quarter or just a little before halfway up the guage. Basically about were it should be. But once I run the heat it will start to climb up past halfway then fall back close to the bottom line of the guage then climb and sit steady at around halfway way up the guage them climb and fall and basically just keeps doing it. The truck seems to be running fine nothing in the oil and no weird color smoke. Its weird.

 

[Justme63]

I am having the same issue, really. I know I have air in the system and still slowly bleeding it out. I found I have a soft upper hose which will be replaced tomorrow. It doesn't seem to be affecting anything though other than making me crazy. If I correct this I will let you know what happens.

 

[Bobmbx]

Ill check both hoses when I get home to make sure they are both hot. And yes Im pretty sure the thermostate is facing the proper direction I have the largest part of it I guess you could say facing into the engine itself. The only thing I'm not sure of is if I have the little hole thats in the ring of the thermostate facing up. But im not sure if that would cause the trouble or not?

Is it possible for some part of the heater to be pulling in air or to have air trapped in the heater core?

And yes its a strange issue. If I leave the heat turned off the guage stays pretty much at a quarter or just a little before halfway up the guage. Basically about were it should be. But once I run the heat it will start to climb up past halfway then fall back close to the bottom line of the guage then climb and sit steady at around halfway way up the guage them climb and fall and basically just keeps doing it. The truck seems to be running fine nothing in the oil and no weird color smoke. Its weird.

Here's a thought. When you have the heat on, does the temperature of the air coming out of the vents change as the temp gauge changes?

Turn on the heater full blast. The temp of the air coming out of the vents should not change. If it does, you got some flow issues.

 

[stafphoto1]

I'll check the heat tomorrow. But I can say that both my upper and lower radiator hoses are getting hot.

 

[stafphoto]

Well drove in to work today and the temp of the heater doesnt seem to be changing as I drive. As a matter of fact when I was sitting in the parking lot the temp guage was a little below half and the heat was still very warm even with the truck just sitting at idle. So I honestly have no idea what the problem is.

 

[Bobmbx]

Well drove in to work today and the temp of the heater doesnt seem to be changing as I drive. As a matter of fact when I was sitting in the parking lot the temp guage was a little below half and the heat was still very warm even with the truck just sitting at idle. So I honestly have no idea what the problem is.

That is good news. It means you've got consistent flow, and the heat is being moved out of the engine. Everything else is just annoying.

Hmmm......did you check the voltage at the temp sensor cable with it connected and disconnected from the sensor?

 

[stafphoto1]

No I haven't I don't have a volt meter handy. Would have to wait until I could get ahold of my dads. I'm almost getting to the point of saying screw it and just keep driving it. I mean I'd like o fix but sometimes it gets annoying to mess with it.

 

[Justme63]

On my last engine I had a thermostat go bad and would stick. The gauge would peg to the top and then come down so that was a different issue. I will be checking the connections and possibly even swap out the sending unit to see if that corrects this pesky guage.

 

[stafphoto]

Ive tried switching the thermostat twice and the temp sending unit once. Still does it. Getting close to just taking it to the shop and having it checked over I dont think a pressure test would be to expensive. At least if I can for sure find out what it is I can fix it.

 

[koda2000]

may it's the gauge itself.

 

[stafphoto]

Ive thought about that myself.

 

[stafphoto]

Well checked the coolant for the hell of it at lunch today and it would appear I am loosing coolant. It must not be to big of a leak though because im not getting any puddles. This is going to be fun to find I think. Hopefully its just the hose that runs from the water pump to the heater its the only one I havent changed. The big upper and lower ones have been changed.