Mitaka

Today I drove my car again and in traffic the temp. indicator started going a little above normal. I turned the car off. after 5 min or so restarted and the temp indicator was way off to the right. The fans kicked in and the temp started to go down slowly. When I started moving temp went to normal. It seems that thermostat and fan works OK. The only things that are different are warmer weather, new coolant and new oil. What do you think causes the problem. This winter I had my mechanic flush my radiator. After I brought him 1 Gal original coolant he said he had to add a few more quarts of Pentosin G12. Wasn't he suppose to put water 50-50 mix. It looked on the receipt that he put mostly coolant. Is it possible that I am experincing higher temperatures due to wrong mix proportion- too much G12 and not enough water. I also did convert to Lubro Molly oil 0W40 oil could that be affecting temertures. What do you guys think? I would hate to have to bring it to stealer for that

ttuling

Yes, too much G12 and not enough water will cool poorly. The system holds 2.25 gallons, so if your mechanic charged you for more than a quart or two of G12, that could be a problem.

But I'd expect poor cooling capacity to show up first at the top of long hills, not when going slowly. (Based on when I had a bad thermostat.)

It's normal for the coolant to be hotter five minutes after turning off the car. We just don't see it on our gauges too often because the thick normal mark covers all readings between 80 and 100 C.

Is the electric fan running when the gauge is a little above normal and the AC off? If you don't know, we can't know that the fan and thermostat are okay, because maybe only the third fan speed (controlled by the temperature gauge) is working. A thermoswitch in the radiator controls the first and second speed. If the fan doesn't run before the gauge rises above normal with the AC off, it could be a problem with this switch, the resistor on the way to the fan motor, or even the thermostat not letting though enough coolant to heat up the switch.

If the fan doesn't run with the AC on, something is definitely wrong.

Also, if you have VAG-COM, you can check that the instrument cluster and engine controller both read similar coolant temperatures, to verify that the sensor for the gauge is good.

I doubt your oil is a problem so long as you have enough in the engine.

Tom

ryoung

Set the climate control display to precisely read instrument cluster coolant temperature.

<a href="https://forums.audiworld.com/a8/msgs/77516.phtml">JimR's Post</a>

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PaulW

Agreed with Tom, if it came back down after restarting the car, everything could be normal

matrixabc

Does yours have a viscous coupling fan?, mine needed some revs to get it going sometimes.

ttuling

though you'd still want to use VAG-COM to check the engine controller's coolant temperature reading if you suspected a bad sensor.

Tom

ttuling

unless it's very hot outside.

Tom

ryoung

Even on slow speed, it should be enough to keep temps normal in this weather. If the fan wasn't running, that's probably the problem. If the fan was running, I'm afraid your thermostat isn't opening fully ... especially since this is the 2nd time the car overheated.

Pure ethylene glycol doesn't transfer heat as well as water (or a 50:50 mix), but I wouldn't have expected problems until hot summer weather.

mclarenm8d

Haven't read through the other posts, my apologies if you have already heard this -

When my thermostat went bad, what tripped me up is that the reservoir was still full. It seems that the car can be very low and the reservoir won't show a problem.

So, the chain of events was 1. bad thermostat, 2. got too hot, 3. evaporated fluid, 4. air in the system so reservoir doesn't represent reality.

From there the cycle repeats to the point one can't drive the car over 2 miles without overheating.

There are actually two sets of fans, you "hear" the ones that kick on when the A/C is on.