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Overheating...coolant temperature too high...STOP!

Posted: Mon May 07, 2012 7:09 am
by jamesy12345
hello all, some advice 1993 480 turbo auto seems to be overheating as the coolant temperature is too high (as above showing temperature above 100 degrees C and occassionally STOP on the dash). At the time the car was being driven fairly gently, and on stopping the was no obvious signs of very high temperatures under the bonnet - after a few minutes i took the expansion tank cap off slowly and nothing exciting happened. Oil temperature seemed OK at about 103 degrees max. The engine type is B18FT 107. Any comments on similar experiences would be appreciated. I guess the most likely candidates are the thermostat or coolant temp sensor....thanks!

Re: Overheating...coolant temperature too high...STOP!

Posted: Mon May 07, 2012 8:53 am
by Robou
The water temperature as indicated by the info centre is measured by the sensor near the thermostat. In the front of the block a double sensor is located, responsible for reporting temperature to the two ECU's and the engine temperature to the info center as well.
From this you may conclude the sensor near the thermostat is malfunctioning or the wire is loose and contacts mass, indicating a high water temperature. This will not have any influence on the functioning of your engine.

Re: Overheating...coolant temperature too high...STOP!

Posted: Mon May 07, 2012 1:35 pm
by jamesy12345
Much appreciated! I am on the the return leg of a 600 km trip...

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Aug 22, 2012 6:32 am
by jamesy12345
I forgot to close this one out.......the STOP :angry: warning did not reappear, even on a very warm day stuck in traffic going to see some Olympians perform.....thanks for comments

Re: Overheating...coolant temperature too high...STOP!

Posted: Sun Apr 23, 2017 4:29 pm
by frenchfries

Ship has decided to develop the same fault, do you have a pic of where I can find this "double sensor" for me to toggle it and see what happens please?

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Aug 28, 2019 7:01 am
by AleksanderHugo
My 480 developed overheating issue as well. It showed “STOP” for the first time about three weeks ago. The car went to a workshop, where they did not find any problems... I hate these issues that appear and disappear randomly :( I was observing the temp reading for few days — it is usually between 88 and 96 degrees, but once it got to 103. That seemed fine, so I got calmer and concluded that the problem is gone :)

Today the “STOP” appeared again, I immediately stopped and observed the temperature reading. To my surprise it dropped very quickly: after a minute it was down to 93 degrees. I continued driving for the next 10 minutes and the readings were going up and down between 90 and 99 degrees.

The top coolant hose is warm, so the thermostat is opened. Radiator is running (at least due to AC being on), so the basic things seems OK.

Could it be a faulty temp sensor? Or perhaps there is an issue with coolant circulation?

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Aug 28, 2019 9:35 am
by JP
Have you got excessive pressure build up in the cooling system? An open circuit will show a cold engine on the info-center so it´s fair to say that you might have cooling problems. It seems a head gasket failure.

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Aug 28, 2019 12:01 pm
by jamescarruthers
Remember that the temperature sensors for the Info Centre display, Engine Fuelling Control and Cooling Fan are three different sensors!

If you have air con, I think you should have a two stage fan and maybe it didn't reach its second stage if the fan temperature sensor there is not switching the second stage on.

To start: I'd be making sure that the two stages are working by forcing them. I'm not sure exactly how as I've never had to do it but I think you probably just have to ground a stage at the sensor to make it work‎.

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Oct 09, 2019 6:23 pm
by AleksanderHugo
I am still struggling with the overheating.

As suggested, I verified that the cooling fan works when bridged. Then, I took the car to two workshops and got plenty of things done:
- new thermostat,
- new 1-pin temperature sensor for Info Center display,
- new 3-pin temperature sensor for the cooling fan control,
- flushed the cooling system, refilled with new liquid and bled,
- they also concluded that the head gasket is fine (based on some CO2 measurements).

After all of the above, I was told that the car seems fine and they have no more ideas what to do. So I took it back. On my way home, the engine temperature rose slowly... until it reached 113 degrees :cry: . Then it fell a bit down and kept oscillating between 100–103 degrees. To my surprise, the cooling fan stayed silent. Is it possible that there is such a big difference in coolant temperature between positions of the 1-pin and the 3-pin sensors? Perhaps the temp that is displayed on the IC is completely wrong?

It is quite frustrating, because it's been over two months since I was able to drive my 480 without being nervous about the temperature.

Re: Overheating...coolant temperature too high...STOP!

Posted: Wed Oct 09, 2019 7:15 pm
by Alan 480
can you get access to one of those Infra red temperature 'guns'

sometimes sold in Lidl / Aldi, if you have ALdi / Lidl in Denmark??

then you can check temperature across radiator/block/pipes etc

or try and get a small probe that plugs into a multi-meter and use that?

100-103 does seem rather high, ours used to sit around 87 - 90 MAXIMUM, since changing the stat sits a bitty lower

Re: Overheating...coolant temperature too high...STOP!

Posted: Fri Oct 18, 2019 8:37 pm
by AleksanderHugo
New developments in my overheating story. I made some inconclusive tests with a laser thermometer — temperature seemed lower than IC display, but I wasn't really sure where to measure it exactly on the engine :?

Then, I decided to test the info centre, which was the only thing that no one looked into. Before, I tried grounding the wire, which gave "STOP" message, but that's all that was tested.

Now, I bought a couple of resistors: 82, 100 and 180 Ohms. I connected them to the wire that normally goes to the 1-pin temp sensor (the other end of the resistor was grounded at the negative terminal of the battery).

Initially, everything seemed OK. With the 180 Ohm resistor and the engine off, the IC displayed 75 deg C. Then I turned on the engine and I tried the 100 Ohm resistor. I waited a bit, because the IC display has some delay before it catches up with the resistance. The IC showed 104 deg — seemed more or less fine. However, then the temp started to grow! :eek: Despite the IC being plugged into a resistor with constant resistance! Just to be sure, I used 5W resistors, so they should not be affected by the current sent from the IC. I also verified their resistance with a multimeter, before and during my tests.

So with a constant 100 Ohm resistance, the IC temp display is going between 94 and 111 C... It doesn't change rapidly — it took few minutes to observe such a wide range of readings. Nevertheless, the temp display should stay constant and not jump nearly 20 degrees. It seems that my cooling system is OK and all of the mechanical work done was pointless.

If anyone has any ideas what could have gone wrong with my IC, then I will appreciate your advice :)

Re: Overheating...coolant temperature too high...STOP!

Posted: Fri Oct 18, 2019 9:02 pm
by jamescarruthers
Dunno really, but if there is a fixed resistance "in" (your resistors) and it varies the temp. value still then I'd be looking at the resistance "out", i.e. the Info Centre ground. I'm only basically trained in electrics mind!‎

I think this is grounded at the alternator connector and probably goes through the instrument cluster multi-pin plugs. How about cleaning both of those up? Contact cleaner on the plugs and brass brush on the grounds at the alternator would be how I would tackle this. 

You sound like you are alright at electronics if you were confident with putting a few resistors in to test stuff so hopefully you'll not be too far off cracking it. ‎