Faulty Coolant Temp sensor or gauge?

[gotdsm?]

My gauge in my car reads hot! Like Overheating hot. So I pulled over and the car wasnt that hot... I parked my car for a day. Started it up in the morning after 12hrs of sitting and the gauge reads hot like the car is overheating. Which would cause this? The temp sensor or gauge? Also where are these located on my car? I heard they are by the coolant cap. Is this correct?

I have a 91 AWD TSi.

 

[echo]

the coolant sensor is under the thermostat housing. the gauge could also be stuck. tap the gauge cluster window and see if it bounces back.

 

[gotdsm?]

The gauge starts out at the left hand side where it is supposed to be and then when I start my car it will immediatly climb to hot. I have tapped the gauge cluster and it still stays the same.

the coolant sensor is under the thermostat housing.

Ok, so where is the thermostat housing?

 

[Defiant]

Under the coolant fill cap, in the thermostat elbow.

 

[Dr.C]

Could be a thermostat that is stuck closed. Turn your heater on when it reads hot. Is the air coming out the vents hot or cold?

 

[gotdsm?]

The heat comes out hot.

 

[gotdsm?]

Ok, I replaced the thermostat with a 180 degree Tstat and it seems to take a bit longer for the warm air to start up. However the guage still reads Hot. Where is the coolant temp sensor that I want to change out that relates to my gauge in the cluster?

I heard that there are 3 sensors. 1 for AC one for the ECU and the other one im not sure of.

BTW, I dont have AC in my car so that should eliminate one of the sensor possibilites.

Thanks again for all your help.

I have a 91 AWD TSi.

 

[Benji]

If you'd have a faulty CTS (coolant temp sensor) you would have a check engine light and would also have starting problems (don't know why, but it happened to me), so it is more than likely the gauge itself ...

Hope this helps!

 

[gotdsm?]

Hmm... The gauge works... Because it starts and cold and then when I start the car it works it's way to HOT. So the temp sensor has to be bad... Only makes since right?

 

[Benji]

Originally posted by gotdsm?
Hmm... The gauge works... Because it starts and cold and then when I start the car it works it's way to HOT. So the temp sensor has to be bad... Only makes since right?

No, just because the needle moves does not mean it's functioning properly and/or is correct.

Like I said, if the CTS failed, you would have an CEL which is code #21 (Engine coolant temperature sensor).



Also, you can test your sensor, just take a look at your manual!

from 1000AAQ
You may be having difficulties with your coolant temperature sensor. This sensor also affects idle, air/fuel mixture, and timing, and failures can generally be detected by the ECU as error code #21. A burned out fan switch or relay may also be the fault.

 

[gotdsm?]

I got my adapter for my pocketlogger today so I will try and pull the error code.

 

[Benji]

Originally posted by gotdsm?
I got my adapter for my pocketlogger today so I will try and pull the error code.

So, do you have a CEL? If you do, then I bet it's your collant temp sensor, if you don't have a CEL, then there is no code to pull ...

 

[97toplessturbo]

I just did a search and found this thread and i was hoping you guys could help me. I have a 2g turbo, the temp. gauge doesn't do anything at all. However, i don't have a light on my dash saying anything is wrong with the actually sensor so i don't know what it is. How do you test the sensor and if that isn't the problem, how do you check the actually gauge? Any help would be great. Thanks.

 

[Thunderskull]

Originally posted by Benji


No, just because the needle moves does not mean it's functioning properly and/or is correct.

Like I said, if the CTS failed, you would have an CEL which is code #21 (Engine coolant temperature sensor).



Also, you can test your sensor, just take a look at your manual!

Actually, there are 3 sensors for coolent. 1 is for the guage on the dash, 1 is the coolent temp sensor that goes to the ECU which throws a code 21 if faulty, and 1 goes to the a/c to switch the fan on. If the temperature guage sensor goes, it obviously won't affect the coolent temp readings that go to the ECU. The guage sensor and the coolent temp sensor share no wiring at all. One will not effect the other. Check your service manual. I've replaced both a coolent temp sensor and a thermostat before. The 3 sensors are attached to the housing plain as day.

 

[gotdsm?]

Ok, I have to revive this thread. I replaced my thermostat with a 180 and it did not fix the gauge problem on my dash. When I turn my key to the ON position my gauge will sweep from left to right to indicate HOT before I have even started the vehicle.

I went ahead and checked for codes and I was unable to pull any.

So I guess my question is.. Should I try replacing the Coolant Sensor or do you think my dash gauge is bad? I dont know how else to tell how hot or cold my car is running and since its such a critical thing I dont want to run my car and blow a headgasket or worse. Any advice would be appreciated.

Thanks again.

 

[Thunderskull]

Ok, I'm taking this right from the service manual for ya. The sensor you're looking for is the one sensor out of the three that's at the very bottom.

1. Remove connector harness from coolent temperature guage sensor in the engine compartment.
2. Ground harness side connector via a test light. (12V-3.4W)
3. Turn on ignition key
4. Check that the test light goes on and the guage needle moves.
5. If the light goes on and the needle doesn't move, then replace the engine coolent temperature guage.
6. If the light doesn't go on and the needle doesn't move, then check for a broken wire.

Now, if the guage checks out, then you know the sensor's toast.


Ok, to test the guage sensor you need to first remove the sensor. Then, heat up some boiling water while you have a multimeter attached to measure resistance. As the temperature increases, the resistance will decrease. The standard resistance at 70 degrees celsius is 104 plus or minus 13.5 ohms.

This is the only sure fire way to test these components. If you don't have a multimeter, you can pick one up for about 12 bucks. A test light's even cheaper than that.

I hope this helps.

 

[hoycoconut]

You said you had a pocketlogger? What does the temp readout on the logger look like??? My guage is flaky and my pocketlogger shows a stable line.

Jt

 

[Thunderskull]

The temperature readout seen on the pocket logger comes from the engine coolent temp sensor. It does not transmit any information to the guage on your dash. It only sensds information to the ECU. You have 3 sensors for coolent. 1 is the engine coolent temp sensor that goes to your engine computer (this records the value seen on the pocketlogger), the 2nd sensor sends readings to the guage, and the 3rd and final sensor is connected to the a/c switch which kicks on that 2nd radiator fan which is usually needed when your a/c is on. This means that your pocket logger can show a steady temp even though the guage is flaky. Follow the procedure I posted in this thread for testing the sensor and the guage so that you can find which is having trouble.

 

[gotdsm?]

It's the second one... I just need some money to replace it now.

What a delima!