Erratic temperature gauge

[Faisal Taha]

Hi every body. Iam new to the forum and hope I can find help here. I have a 2008 explorer .last week I had the engine completely changed as suggested by mechanics.Since then the check engine lamp is on! The car was running fine. After computer check , they said the fault is in the temperature sensor which I changed last night. Today driving to work the temp. indicator suddenly changed from the normal half to H .I stopped the car , the coolant level was full and I could open the radiator cover without coolant spilling or bubbling. After an hour I started the car and the gauge was down to zero , I moved and the gauge was oscillating between zero, half and H all the time but the car was running fine !! Appreciate your response and please keep it simple as my knowledge about cars is almost zero.Iam an expatriate in Saudi Arabia where it is blazing hot , so Iam worried to even start the AC.

 

[974X4BLACKSPORT]

Check for a stuck closed thermostat. If your engine is at operating temperature and the upper hose is not hot, then the thermostat is stuck closed. When water is flowing in the radiatior and the thermostat is open the top hose will be hot, and the bottom hose going back to the engine will no be nearly as hot.

 

[Faisal Taha]

Appreciate your help..will check and give feedback.. thanks a lot

 

[PotatoExplorer]

I think it's probably more than likely air bubbles trapped in your system then a thermostat problem. A huge fluctuation in temperature on the gauge in a short amount of time makes me think this whereas a stuck thermostat would have your engine running too cold or too hot with the temperature being accurately displayed on the dash.

There's plenty of posts about this but in short - elevate the front end (I parked on ramps), open radiator cap making sure the engine is fairly cold unless you like to burn your face off, jam a funnel into the top of the radiator where the cap was (I wrapped electrical tape around the outside of the bottom of the funnel so it would be a more snug fit. The funnel is going to act as a reservoir as the coolant expands), start the vehicle and let it sit for a few minutes as it gets up to normal operating temperature, hold the engine at a higher rpm for a minute or two to get her nice and hot, turn on the heater to max temp and fan for both the front and back (if you have rear heat), give her another round of revs, get out and massage the upper and lower radiator hoses to work out any trapped air bubbles, turn off the heater and maybe do one last bit of revs. At this point you should have most of the air out of the system. What I did to close the radiator cap was jam a rubber stopper on a long screw driver, submerge it into the coolant in the funnel and then pressed it down into the bottom, lift the funnel up and dump the excess coolant into a bottle. Coolant will be nice and hot. Replace radiator cap.

Hopefully this will help you. If not, you may need to drive her around a bit more and do a 2nd round of this.

 

[Faisal Taha]

Thanks a lot for your suggestion and taking the time for it. However, just came back from the electrician who found a bunch of wires going into the heat sensor which were bare and in touch with each other . After insulating each, the gauge went back to normal.The other thing is that the check engine lamp is always on since I changed the engine. The car is running fine and the mechanics couldn't spot the cause for that even after computer check !!! So Iam just driving with the lamp on though really worried ...Thanks again.

 

[Munchie]

Thanks a lot for your suggestion and taking the time for it. However, just came back from the electrician who found a bunch of wires going into the heat sensor which were bare and in touch with each other . After insulating each, the gauge went back to normal.The other thing is that the check engine lamp is always on since I changed the engine. The car is running fine and the mechanics couldn't spot the cause for that even after computer check !!! So Iam just driving with the lamp on though really worried ...Thanks again.

Glad you figured out the temp gauge but the light being on and not knowing why is not right. The mechanics should be at least able to tell what codes are being thrown and then you can troubleshoot from there. Can you get the codes from them? After the recent issues I would also recommend clearing the memory. I use a scanner for that now but pretty sure you can disconnect battery and leave for 10 minutes to do the same.

Did these mechanics install your new motor? I would think they should be doing the work to find out what's going on now if that's the case...

 

[Faisal Taha]

Thanks again for your prompt response.Actually they cleared the memory after I changed the heat sensor which they suggested was the cause of the check engine lamp persisting.I also tried disconnecting the battery for an hour , but again the lamp lit after sometime! I think they are stuck and cannot explain the problem if any.They suggested that I continue driving as long as the car is running smooth! Actually not very reassuring but I tried mire than one mechanic . I have a long drive after tomorrow ( 800 km) .I hope everything turns out alright !!

 

[PotatoExplorer]

You have to clear the PCM doing this:


Just pulling the negative terminal doesn't clear everything like in older vehicles.

 

[Munchie]

Thanks again for your prompt response.Actually they cleared the memory after I changed the heat sensor which they suggested was the cause of the check engine lamp persisting.I also tried disconnecting the battery for an hour , but again the lamp lit after sometime! I think they are stuck and cannot explain the problem if any.They suggested that I continue driving as long as the car is running smooth! Actually not very reassuring but I tried mire than one mechanic . I have a long drive after tomorrow ( 800 km) .I hope everything turns out alright !!

Get the codes from them. If the CEL/MIL is on there is a code.

And reset as per the above.

 

[Faisal Taha]

You have to clear the PCM doing this:


Just pulling the negative terminal doesn't clear everything like in older vehicles.

 

[Faisal Taha]

You have to clear the PCM doing this:


Just pulling the negative terminal doesn't clear everything like in older vehicles.

Thanks again. Hopefully I can try that tomorrow. Video was helpful.

 

[Faisal Taha]

Get the codes from them. If the CEL/MIL is on there is a code.

And reset as per the above.

Thanks very much. Hopefully I will try to do a scan tomorrow and get the codes.