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Overheating issue

Rishodi

CEG'er
Joined
May 18, 2005
Messages
418
Location
Durham, NC
This is the latest chapter of my adventures with the CSVT. Last night I was driving to pick up a friend when suddenly I noticed that my temp gauge had gone all the way to the right, so that it was almost horizontal. I immediately turned the heat on full, which brought the gauge back down to the normal range in a matter of seconds, and pulled over to turn the car off as soon as I could. I popped the hood to check the coolant, and it appeared fine. I couldn't find any leaks, and it seemed to be at the same level I had last filled it up to. I didn't notice anything else unusual. I dropped my friend off and started to go back to my place when the gauge went up again - with the heater still on - and stayed that way. I pulled over again and popped the hood for a few minutes to let the engine cool before driving the last couple of miles back to my apartment. At this point the gauge was still on the hot side, but not as far right as it had been when I first noticed an hour or so before.

Now, I'm not too familiar with the coolant system, but if I remember correctly, if the water pump was broken then the heat would not work. The heat works as well as it always has, so that's out. The first thing we did this morning was replace the thermostat, which was the first suspected culprit. However, we tested the old one by putting it in boiling water and it seemed to work just fine. As of this morning there are a couple new leads. First of all, the temp gauge is stuck at about the same point it was last night when I pulled in and turned the car off. It didn't move even though the car had been sitting all night long. Secondly, the radiator fan may not be working. I let the car idle for a while to see if it would turn on, and though I could hear a click that I assumed to be the fan relay, I never heard the familiar whir of the fan. I drove the car around town for a few minutes to see if the gauge would move at all, and unlike last night, it didn't.

Note that this entire time, there have been no obvious signs of overheating. No boiling or overflowing fluid in the coolant reservoir, no odd smells, no smoke, nothing. I could only assume that the engine was overheating because the temp gauge said so before it died. While driving around this morning, the engine warmed up enough to put out hot air through the vents, but it was no hotter than usual. Afterwards I checked under the hood again, and still everything appears to be fine. To err on the side of caution, I won't be driving it until I get this problem figured out.

So at this point I have two main thoughts: First, I either have a bad gauge or a bad sensor, since as of this morning the temp gauge is obviously no longer working. Secondly, I might also need to replace the fan, which hasn't been turning on as far as I can tell, even when the car is sitting still idling. Since the most experience I've had with the coolant systems on these cars to date is doing a flush, I figured it couldn't hurt to see if anyone here had any useful input. Thanks to all in advance.
 
the coolant temperature sensor sends information to the computer, the computer then turns the fans on and also sends the info to gauge in the gauge cluster. Basically it sounds like you need to replace that coolant temperature sensor.
 
the coolant temperature sensor sends information to the computer, the computer then turns the fans on and also sends the info to gauge in the gauge cluster. Basically it sounds like you need to replace that coolant temperature sensor.

Half way correct. There are actually 2 sensors. One sends the temps to the PCM which turns on the fans. The other sensor is strictly for the gauge.

Are you absolutely sure its overheating? I think its the guage sensor. If it was literally pegged in the red, when you opened the hood you would hear the coolant boiling and the coolant would be spewing.

To me it sounds like its the sensor for the gauge or the wiring to the sensor. If you unplug the wiring/connector (its a 2 pin connector with only one wire) from the sensor it should tell you what's going on. With it unplugged the gauge should shoot all the way to left. If you jump the 2 pin connector by putting one end of a wire in one pin and the other end of the wire in the other pin, the gauge should shoot to the right. If it does both of these, then I would say your actual sensor is bad.

Make sure you test the right sensor. Luckily, the sensor for the gauge from what i remember is directly under the throttle body. It's pretty easy to unplug the connector. Remember, it only has 1 wire but its a 2 pin connector. The other ECT sensor not to be confused with that runs to the PCM runs to a 2 pin connector with 2 wires.
 
... I either have a bad gauge or a bad sensor, since as of this morning the temp gauge is obviously no longer working. Secondly, I might also need to replace the fan, which hasn't been turning on as far as I can tell, even when the car is sitting still idling. ....I figured it couldn't hurt to see if anyone here had any useful input. Thanks to all in advance.


If you have an early model E0 check the condition of the fan wire harnesses. Check to see if the fans turn easily and aren't seizing.
Easy test to see if the fans work is to turn on the A/C.
 
If the problem was solely the sensor though, isn't the gauge springloaded so that it should return to the left when the car is shut off? Because that isn't what happening - the gauge sits on the far right even when the car is off. Thanks to everyone for your comments btw.
 
If the problem was solely the sensor though, isn't the gauge springloaded so that it should return to the left when the car is shut off? Because that isn't what happening - the gauge sits on the far right even when the car is off. Thanks to everyone for your comments btw.

No, it will not return. It will stay where it's at when the car is shut off.

Have you unplugged the wiring and checked to see if the needle pegs to the left?
 
BTW, let me reiterate my last post.

I'm pretty sure all the pre 98 temperature gauge's would go back to the far left when the engine was turned off. My 96 did.

My 99 and my brothers 00 do the complete opposite. They stay where they are at when the car is turned off. The next morning when the engine is cold and you turn on the car, the needle goes back to cold. I would assume the 98s were like this although I suppose it would be possible that the early model 98s could be like the pre 98s. :shrug:

Regardless of the case, I don't see a guage getting jammed.
 
If your radiator fan works fine, then it could be the thermostat. As for the temperature gauge, change the temperature gauge sender. Then if the temperature gauge still will not return to cold, change the temperature gauge. All this, of course, assuming that you don't have a wiring harness problem.
 
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