Engine Temperature Gauge Adjustment
 

My mechanic just tuned up my cooling system, and one of the things he did was to adjust the engine temperature gauge reading. However, now it reads too low. When I start the car in the morning the temp gauge is about 1/4 inch below the cold mark, and during the day the gauge only gets up to the lower normal reading.

I can take the car back to him to have the gauge readjusted, but I was thinking this should be something I should be able to do as well. Does anyone here know how to adjust the engine temp gauge?

Also, I have an infa-red temp gun and would like to check the temp of the engine from time to time. Where should I take an engine temp reading? I was thinking of the thermostate housing, but there may be a better place. Any advise?

The Temp sensor for the Instrument Panel is on the drivers side of the thermostat whilst the temp sensor for the ECU's are on the passenger side and have a blue plug. Someone will correct me if I am wrong I am sure.

I used a IR gun on the two sensors and then compared them with the Instrument Panel and the ECU temp read out via a Hammer. The Instrument Panel sensor reads slightly less as it is on the return path from the radiator.

My car temp on all sensors and Instrument Panel is between 83c and 89c at all times when fully hot.

An interesting observation is that when my upper radiator hose clamp failed recently and the hose blew off the temp never rose much as the stock thermostat was only just open and only 4 litres of coolant was lost.

With the alternative lower temp thermostat the situation would have been very different.

I just checked and you are right. The sensor on the passenger side is blue while the sensor on the drivers side is brown. I'll take my readings there. Thanks.

As for adjusting the engine temp gauge, I'm concerned I would have to remove the instrument from the cluster, and that is way too much for me to attempt. If there is an easier way, I would like to know it.

He may have added a resistor to the temperature sensor wiring.

When you measure the temperature from the water bridge (with the IR gun), make sure that the fans are not running and that there is no other hot air interference or you may read higher temperatures. If the air is hotter than the water bridge it will measure the air temperature instead.

Pod removal is not very hard:

http://www.rennbay.com/odotutorial.html

It would help to know your model year (MY). Usually people put that in their signature.

If you do remove the pod it's just a matter of adjusting the needle by hand. Easy-peasy. Good luck. :)

I doubt a mechanic would spend all that time removing the pod when he can spend 5 mins adding a little in line resistor at the temperature sensor :)

Hmm... good point Phil. Perhaps the mechanic that adjusted the guage reading to begin with will tweak it to spec as warranty work.

Flyrade,

Please advise what year 928 you have - if it has a digital dash there are 'clever' things you can do.
In my opinion you should be running the standard oem temperature rated thermostat. I forget what temp. rating these are. (is 89 C correct?)
You should check the water tmp with an infra red gauge with the engine at full operating temperature. One good place to check is the top radiator hose, which carries hot water to the radiator before it is cooled. Worth comparing cam cover temperatures too
You need to be mindful of 'emissivity' -different readings for different levels of surface reflectivity. Arguably best way to allow for this is to simply test a range of other 928s after a drive that would thoroughly warm up the engine.
Once you are 100% satisfied that the engine is operating at the correct temperature but that the gauge is misreading it is then a relatively simple job to remove the pod, pull the needle off, and put it back on in a slightly different position so that normal engine temp the gauge points to the middle

From the above:
1. I have an 89 red/tan/5-speed. I would like to make a signature to include this info, but don't know how to do it.
2. I would also like to have a photo of my car with my name on the left side of all my posts - again, I don't know how to do that as well.
3. I would not feel comfortable removing the pod because I am not that experienced working on cars. I would be concerned I would do more harm than good. But thanks for the info, and I enjoy looking at the sequence to remove the pod. I appreciate everyone's response.

At the top of the screen on the left side, click User CP. You will see a list on the left. Click edit signature and you can enter your details. Click edit avatar and you can add the photo of your car.

With 89+ the car has the digital dash daveo mentioned. Using the digital dash diagnostics, the temp sensor readout versus Ohms can be determined and the temp gauge could be "calibrated" by adding a resistor, as others have mentioned. I would ask the mechanic what he did and why and let him know you think it's not correct.

OK - got it. Thanks.

I may be wrong but I think you need to be a financial member to have a signature but you can have your avatar

Oops only just realised this was an old post