On my 1995, A6 with 2.8 engine I have 197,000 miles. The ECT has never been changed. For at least 10 months I've observed the dashboard temp gauge rests all the way to the left, ( cool position ) It may move up a little after driving for about 15 minutes, about one needles width. It isusually indicating in the cold area of the gauge. Sometimes after I stop and idle for a few minutes the needle will move up to the right about 40%. Once I resume driving it will again quickly move down to the cold indication.

Finally had a chance to look at the Bently manual which shows both an ECT G62 installed in a large coolant pipe and an Electronic Engine Coolant Temperature (ECT) thermal switch F76 also in the same coolant pipe but on the passenger side of engine. I only found the one shown as G62 in the drawing. It is on the driver's side in the coolant line behind the cylinder head. I took a few photos. The unit I suspect is the actual ECT is not Green or Black or Blue. It looks like a faded light yellow and I don't think it just pulls out. It has a hex nut nearest to the pipe it is installed in. It has just2 electrical terminals which agrees with the manual. Also made some resistance tests.

I waitedabout 15 minutes after engine shut down to make measurements with my ohmmeter. The ambient temperature outdoors was 38F during these tests. I measured 650 ohms. I then started the engine and ran it for 2 minutes, shut it off and remeasured. It now read 1,275 ohms. It appears the resistance is rising as the coolant gets warmer which is contrary to what the manual indicates. It says, "At approx. 20C coolant temp, approx 2.5K ohm and at approx. 80C coolant temp, approx 330 ohm.

BTW, this unit was very easy to get to for these tests.

I then placed a 370 ohm resistor across the two pins of the connector socket. Turned the ign. on and saw no movement of the temp gauge. Started engine and it ran a little rough. Did the same test with a 680 ohm resistor and still no temp gaugemovement. I thnk the wiring from the sensor connector to the gauge is intact because when the gauge needle does move, it is not bouncing around like it would if there was an intermittent connection in the wiring.

Here are my questions.

1. If you can see the 2 photos, is this part indeed the ECT that sends signals to the Dash Temp gauge by varying it's resistance?

2. How come the temporary connection of the 2 different resistors had no effect on the temp gauge indication? Needle stayed all the way to left during these resistor checks.

3. I've only seen mention of a black, green or blue sensor color and those have 4 terminals. Does this engine use just a faded white or yellowish looking ECT with 2 terminals? That is what it looks like to me.

Thanks for any suggestions.


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1. Not sure but it looks like some kind of temp sensor or switch, but doesnt seem to be acting like either acording to your tests. Check your wiring diagram and the wire colors against what you have in your car. That may help identify what you are looking at.
2. That makes me think that is not the sensor for the gauge or that you have a gauge issue as well as a sensor issue.
3. Never seen a two wire sensor but most all of my experience is on newer cars.

 

Dankhoud...thanks for help. Further research in Bentley manual shows two items that may be confused with each other. G62 called an Engine Coolant Temperature (ECT) Sensor and F76 called an Electronic Engine Coolant Temperature (ECT) Thermal Switch. Both are shown with the designation (ECT) which can be confusing.

The G62 has 2 terminals and the F76 has 4 terminals [ T, R, + and C ]. T= Coolant Gauge Control. R= A/C Compressor Cutoff. + = Voltage Supply. C= Coolant Overheat Warning symbol.

Manual says to use tester VW1301 but I think use ofa 40 ohm resistor from terminal T of the connector socket for F76 to ground should also cause an indication on the temp gauge of 230F (110C). Obviously it is F76 that controls temp gauge indications. I have not been able to locate F76 yet even though manual gives location. Must be under some other components.

I'll try the resistor test. If gauge reads properly, then F76 must be faulty.

Now I wonder what G62 Sensor is controlling as it's resistance changes with temperature variations.

 

12-23-07 I put car into garage. About 45F in garage and raining outdoors. Engine ran no more than one minute. I had to remove the air hose in order to get to F76 the Electronic Engine Coolant Temperature Thermal Switch. Took photos when doing following tests. I pulled off the rubber boot covering the connector. I see only 3 wires coming out of the connector and I confirmed that in Bentley manual wiring diagram. I put single resistors from ( terminal T ) the Brown/Yellow wire of the connector to ground and then turned ignition on and observed gauge. I did not remove the connector from F76. My test resistors were in parallel with what ever resistance the ECT was at.

My gauge has no numerals, just a series of vertical lines. A 370 ohm resistor showed no meter movement. A 43 ohm made gauge needle move to the 2nd large mark. A 20 ohm moved needle 1.5 lines past the 2nd large mark. A 10 ohm moved needle to about 75% scale. I then removed test resistor and measured resistance from terminal ( T ) to ground. This measurement should indicate the actual resistance to ground of the ECT’s ( T ) terminal. It measured 496 ohms. Bear in mind, all my gauge photos are showing total resistance of my test resistor and the ECT’s 496 ohms in parallel with the test resistor.

So it appears my temp gauge and wires to it are all working. As my upper radiator hose seems just warm to the touch after driving 25 minutes last night with ambient temps of around 35F, I think thermostat may be stuck full or partially open. It was supposedly installed about 8,000 miles ago by mechanic. Who knows what he did? My heater seems to work but does not seem to be getting the air as hot as it used to. Maybe I have a defective ECT F76 and a bad thermostat? Any thoughts out there?

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I would get a resistance reading of the temp sensor with the engine cold. Youll have to disconnect the sensor to do that. It should be at least 2.5k ohm as you stated earlier. The 496 you measure is to low. You may also want to try your resistor test on the connector with it disconnected. Connecting in parallel can cause strange actual resistance measurements in the gauge which do not give an accurate measure if the gauge is working properly or not, however the fact that it indeed moves seems to indicate its doing something so its not completly dead and the wiring is good. You may be on to something with that warm/not hot upper radiator hose. After 25 min of driving you shouldnt be able to hold that hose for more than a second or so topps. Maybe the new thermostat is bad.

 

Thanks for suggestions dankhound..... I tried getting what looks like a purple colored holding clip removed from the F76 Connector body with no success yet. Any simple way to slide that clip out? The connectors with the metal clips that you simply press inwards to release are certainly much easier!

After one hour of 60 mph driving last night I felt those metal loops on top of engine ( see photo ).They seemed only luke warm, no more than about 80F I'd guess. I seem to remember that area used to get VERY hot after driving for an hour. Too hot to keep my hand on it. I also measured the temp of the coolant in the expansion tank as 148F. I don't know if the temp of coolant in that tank is indicative of coolant temp running through engine or not. If it is, 148F seems way low.

When looking at the expansion tank which is new,(original one cracked at hose outlet) the coolant has a brownish sediment in it. I can see small piles of the sediment on the tank bottom andit is coating the sides of the tank. Maybe it is rust particles. I checked the coolant withone of those five floating ***** indicators and it readsthat I have protection to +5F. That is N.G. obviously since I live in NY.

I bought some red Pentosin coolant yesterday and some distilled water to mix 50/50 with.

Now I am thinking the themostat is sticking open and it could be caused by this brownish sediment that is circulating through the system with the coolant.

Even though the Bentley manual (section B19-1) says no need to remove thetoothed belt to change thermostat , the job looks like it is tricky. Before I go through changing of the thermostat (now has 30,000 miles on it...I thought it was newer than that), I think I will flush the sytem with plenty of running water both with engine off and then while running. Then close the drains and try to see if there is any change in engine temp gauge with just water in the system. If no change, then I'll change thermostat and refill with 50/50 coolant and hope that fixes the problem.

Also had another idea of squeezingthe lower radiator hose shut temporarily with a clamp and then watching the temp gauge with engine running, feeling top of engine to see if it get hot, etc. Any thoughts on that scenario?

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Today installed a new Thermostat. When I looked at the original, 197,000 miles on it, I could see it would stay open about 3/32" when cold. This failure to close completely appears to be the cause of problem.

New thermostat gives proper Temp gauge readings (around 90C area). Needle stays right on that mark during idle and highway speed driving. And now I also get heat like I used to before I started having this reduced heat, low temp gauge readingproblem.

So it was not ECT Sensor G62 or ECT Sender F76..... just the thermostat. I used only water in the system instead of 50/50 coolant/water mix until tommorow when I will flush coolant system again and then fill with proper coolant mix.

Outside temps around 34F today. Idrove for 1 hourand temp gauge read normal. That is first time in a long time. I thought mechanic had changed my thermostat about 30,000 miles ago when the timing belt and water pump were changed. After further investigation, I found they never did chage the thermostat. This was the original removed today!

 

It took about 2 hours to properly flush radiator and engine until water ran fairly clear. I continued to see tiny rust particles but these were very small after 2 hours. This is probably first real flush in 12 years. I used hot water about 130F to flush.

Removed the engine coolant drain plug which is a little tricky to get to. I had to jack up driver's side of car in order to wiggle underneath the area where this plug is. Be certain to use a new O-Ring if you remove this plug. Use one made from Viton which can handle hotter temps than standard rubber O-Ring. I got an additional load of water ( 1.5 - 2 litres ) out of that drain but it took 24 hours of letting it slowly drip out. I was able topour in very close to 8 litres of Pentosin G12 pink coolant with distilled water. A50/50 ratio. Engine still running good now and great heat!Temp gauge still showing correct now after warm up.

See the photos of the Engine Coolant Drain Plug the location of the radiator plastic drain mechanism and the location of the Engine Coolant Drain Plug.

My Cold-Chek floating ball indicator says I am protected down to -10F instead of -36F which is what Pentosin claims on their bottle when a 50/50 ratio. I have spoken to the people that make the Cold-Chek indicator and they are going to check Pentosin G001200 themselves with their tool and get back to me.


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