jktt

My 2001 Audi TT 180 hp FWD has been operating at low temperatures for quite a while. I have a Scan gauge connected to the diagnostic port and it indicates the temperature to be about 166 Deg. F. The temperature gauge in the car shows the temperature to be at least 1 notch below the center point. Attaining the 166 degree temperature takes about 15 to 20 minutes of driving, which seems somewhat long even though I am driving in an area where the outside temperature is about 60 Deg. F. What is interesting is that at this "operational" temperature both fans are on. I am not really sure at what temperature they really are supposed to kick in, so this may or may not be part of the problem. My first thought was that the problem was the ECT sensor. I recently replaced it, but the low temperature indication is still there. My next thought is that it could be a thermostat, stuck in an open position. What puzzles me though, is that the one time I drove through a hot climate area (110 deg F), my temperature peaked at 206 deg F. I cannot explain this except to assume that the thermostat is behaving erratically and somehow went from an open position to a closed position when it should have obviously stayed open. I would appreciate any suggestions that would help me resolve this problem. The car has only 37K miles on it. Thanks for any help you can offer.

AudiMick

These cars often have cluster problems specifically the temperature and fuel gauges.There was a recall on the clusters (expired) So run the Vag.com Diagnostics and check the cluster. Their is also a test to check the ECT agrees with the gauge and the ECU.

With the AC off only one electric fan should run at normal temps. There is a thermo-switch in the radiator to regulate the fan. There is a also a fan control module that controls all of them.

Both of these items fail a lot.

jktt

Thank you for your response. My Scangauge reports information from the ECU, and there is correspondence between the Scangauge readings and the gauge. Low Scanguage readings are reflected in the same manner on the gauge, as well as high readings. From this I assumed that there is agreement between the ECT, ECU, and gauge. Nevertheless where can I find information on the additional test you mentioned to check whether the ECT agrees with the ECU and the gauge?

AudiMick

It's a VAG.com thing, no idea on scangauge.

From your results it sounds like the gauges are good.

It's probably either the thermostat or the fan thermo switch/ controller.

Your car has low miles but is 10 years old.

Get an OEM thermostat and install it. It's a bit awkward but 45 minutes with the right tools.

The OEM Audi/VW thermostats tend to fail open, aftermarket fail closed (with sometimes catastrophic results).

If that doesn't help investigate the fan situation.

jktt

I did some research and discovered the 49C procedure. Ran that this morning and there was good correspondence between the Scangauge, dash gauge and 49C readings. Scangauge read 166 deg F, dash gauge was one notch below center, and 49C reading was 75 Deg C which converts to 167 deg F. So the sensors and instrumentation check out, and it does seem as if this may be a thermostat issue. The one thing that is troubling me however, is that at startup when the car was cold, neither fan was working (that is normal), but when I got home, and while in the 49C mode at 75 deg C, both fans were on. Is that proper operation?

jktt

Did additional testing with the climate control off. Both fans stayed off and the temperature climbed, until at about 204 deg F (Scangauge reading), both fans kicked in. So now I don't know if it is the thermostat that is preventing the engine from attaining proper temperature, or the fact that I always have the climate control on, and with it on, both fans are engaged keeping the engine below temp.

AudiMick

Sounds right, the AC always turns the fans on.

FYI the plastic fitting over the thermostat become brittle over time, they can break or leak . Cheap part but very annoying. Make sure you use Audi/VW coolant as typically the parts store stuff doesn't mix well.

I don't know if you have done the water pump/ tensioner/ timing belt service. Your car has low miles but 5 years is the recommended replacement.

jktt

Thank you for your help on this issue. I'll be getting a new thermostat next week. From what you are saying, I should also get the thermostat housing. I've also read that to play it safe I should get the dipstick tube extension. I have the Pentosin G12 (red) coolant, so at least I am all set in the coolant department.

I have not done the pump/tensioner/timing belt service. I wonder if the 5 year replacement recommendation you mentioned is based on expected typical mileage in that time frame, or on parts wearout strictly due to age and/or mileage. I will have to explore this further. Not something to look forward to.

AudiMick

It's a turbo car, lots of heat in the engine compartment. That tends to shorten the life of rubber components.

Depending on where you live and the local climate and whether the car is garaged can make a difference.

In 2001 Audi was using plastic water pump impellers and those original ones are known to break up. The tensioner was a high failure point.

I have owned Audis for over 15 years so having seen this happen I tend to err on the safe side.

With that car I would be looking at changing it within 1 year. If you can DIY it's not really that bad . I have done other FWD transverse cars and it's about as easy as a Honda or Toyota.

jktt

I live in a cool climate and the car is in the garage most of the time so that should help somewhat. For my future or near future reference, what supplier of timing belt kits would you recommend for this job (ECS tuning, Dieselgeek, etc)?