I found this thread but it didn't quite answer my question:
https://www.audiforums.com/forum/aud...s-sensor-4344/

The way I see it, there are a few different types of coolant temperature sensor devices, there are (please correct me on errors because I am not sure):

• Engine coolant sensor - senses an overheat condition, more like a switch than a sensor, this probably is what signals the info panel
• Temperature sending unit - this in a variable resistor that probably feeds the temperature gauge
• Cooling fan switch, this senses a particular temperature and turns on cooling fan

Now to my issue, after my timing belt/valve cover gasket repair, my info panel says I am overheating right at engine start (technically 30 seconds later or so). My temperature reads normal, cold when cold, dead on halfway when up to temp. What did I do wrong? I changed the radiator hoses and the lower does have one of these sensors but I am unsure which one. It is plugged in but maybe I should clean contacts?.

98 Audi A6 Quattro
2.8 litre 30v - Tiptronic
184,000 miles

Thanks,
Rick

 

Does it show overheating when you first start in the morning? Or after a drive and a restart?

 

All the time from about 30 seconds after I start the car in the morning (this morning it was 12 degrees F so there is no way it was hot). The info panel overheat indicator stays on constantly but the temperature gauge reads normally.

 

I just looked at the following thread:
https://www.audiforums.com/forum/aud...symbol-178006/ and realized the info panel is not telling me I am overheating but rather that it detects my coolant is low, is there a sensor for that? (I would have expected yellow for low coolant, not red but....)

 

Check the connector at the bottom of the reservoir.

 

Yep, gonna check that as soon as I leave work, I definitely had the reservoir off while doing the valve cover gasket. I think the thing that threw me was the fact it was a red warning, I thought for sure that was indicating that it was overheating, not just low on coolant.

Thanks for your help hxgaser,
Rick

 

Yep, I didn't plug in the coolant sensor on bottom of expansion tank, to be honest, I really don't remember unplugging it but I guess I did.

All set now, thanks for the help, looks like I delve into front end work next, I have parts already waiting :-)