AudiQC

To ianjax
I didn't realy had problem with the reading of my coolant/water temp gauge reading while i was experiencing some overheating in the past year. My car was overflowing from time to time. Mechanics and even the Audi dealer could not realy point out the problem. I knew it was getting hoter than normal because my engine oil temp was raising up to 120C and even up to 130C in steady high speed 75-80mph. I finaly got the answer when i had my timing belt change 2 months ago and put a new "cap". I had no more overflowing or "boiling" signs and sounds...but oil temp was still getting high /higher than what i consider normal. In heavy conditions though as the oil temp was getting higher and higher than the coolant/water temp was going up to 110C and i was having overflowing and "boiling"......

Now everything is "down" ...oil temp is never higher than 115C, coolant/water temp stick to 90C even at high speed and AC on. As previously mentionned the next step it to realy test it with towing my camping trailer.

ianjax

my oil temp never goes more than 230f even on 95/100 degrees weather here in florida even when overheating !

AudiQC

[QUOTE=silverd2;24484832]The boiling point of a proper coolant mix is WAY higher (270F +) than water's boiling point (212F or 100C) and even higher while under normal system pressure.

So looking for boiling coolant won't help much....while still sealed in, even very overheated coolant won't be boiling. A cap releasing coolant from a way overheated motor is not "boiling over", it is releasing pressure at a set level.

I understand your point about boiling points!! and you are right....On the other hand you must admit that in some area in the coolant/water circuit (engine-radiator-etc) the liquid will or can go up to 260F +, then "boiling" may occurs, creates bubbles and raise pressure in the system beyond 14-15 psi which will make the "cap" release the mixture and produce overflow.

My p.o.v. is if oil temp is "normal" at 110C up to 115C or 230F or even 240F and never get higher...how can you have indication of overheatin in the cooling system, if all fans and water pump work properly. If the engine cooling system doesn't work properly the engine temp and the oil temp will definitively raise higher. It doesn't seems to be the case in Ianjax's case.

ianjax

today i did the on-board diagnostic on the climate control and figured that the reading i was getting on my scanner is the cluster reading ! it was showing 105C for the cluster reading (exactly # the same i have on my scanner) and 90C for the ecu reading... cluster was going up and ecu reading didnt change and stay at 90C all the time !!! so that's for sure that am i having a false overheating ? is this diagnostic accurate ? oil temp stay right bellow 225 ...

Prospeeder

yes, your green temp sensor is bad/defective

PetrolBear

105C is overheating. The dashboard has an average based on different signs, so it is reliable. In case the dashboard shows 98C Grade Water temp, in the Cylinder head there is 4-5 C higher so it is a slow burn out of the head gaskets.
Test your auxilliary fans whether they operate. Mine were going fine although I often had an "overflow" of the water temperature almost reaching 100C in case of (i) idling after a ride @120km/h and also while parking, 10 minutes after stopping the engine.
The auxilliary fans were definitely operational and OK.
The solution was: changing the OEM radiator to a (strictly OEM!) radiator.
This lead to 10C fall of the water temp (due to get free of the contaminations of old one) and a further 5-7C grade fall in the oil temp was done by using full synth 10w50 oil. In practice, oil temp never exceeds 101-103C even at 90miles per hour at 35C grade with AC, and water temp never exceeds 90C even after stopping the machine.

ianjax

ok... so the cluster reading is right and IT IS overheating even if the ECU is reading 90C all the time ?

AudiQC

But don't forget that your oil temp seems to be normal or very close to normal. So if it doesn't reach 225F on heavy load (high speed or towing a trailer) your "engine" is not overheating......
Last year and up to 3 months ago my coolant/water temp (on the cluster) was always at 90C even when my oil temp was close or at 120C or 250F(US) and i was getting some overflow from time to time maily because my "cap" was not or partly doing its job. But anyway! there was something wrong in the whole cooling circuit (radiator, engine, pump, etc) because the engine was too hot. As mentionned before it was only at extreme conditions that the cluster temp indicator was showing temp over 90C.
The flushing and cleaning of the whole circuit realy improved the operation of both the radiator and the circulation of the coolant/water. Now i am getting normal or close to normal temp all over....Yet i have to test it on heavy load ....in towing my Camping trailer in hilly area.
Hoping it help you.....

AudiQC

Here is the test to come

silverd2

There are 2 separate sensors (4 wires) in the double coolant sensor. It is VERY common for one to go bad and other OK...one sends to the cluster and the other to the ECU for engine management functions.

If the temp signal to the ECU is not the same as the temp signal to the gauge, the sensor is bad.

It's incredibly cheap and incredibly easy to change...I swapped one on my wife's AR, when she started getting impossible readings on the gauge, high and low. I had to swap in a new one on my D2 before that, which showed overheating when it was not...I went directly to the temp sensor with a multimeter that time and read 2 very different readings from one half the sensor to the other.

If all else fails, the sensor swap is a cheap easy test or fix.

Part number is 059919501A...OEM brand is "Elth"...I don't know if that's the best, but it's what I used and no problems the last 20K miles.

http://www.ebay.com/sch/i.html?_trks...at=0&_from=R40