'99 ES300 temp gauge mystery
 

Hello, '99 with 195K. This problem has persisted for a few years. Engine coolant temp gauge shows a tick over 1/3, normal. Jump on freeway, and temp will dip to about 1/8 indicated. Get off freeway, and needle will slowly rise to normal position. Does this in summer and winter weather here in SoCal.

Any BTDTs? Just did the knock sensors, and saw 2 temp sensors (?) by the water inlet. Water level in car seems fine, radiator cooling fans operate normally. Suspect temp sensors, or other problem? I appreciate any thoughts.

Bad thermostat? There are two temp sensors (by coolant cap) the one with a single wire connector is for the gauge, the other for EFI.

i had similar symptoms. it was a bad thermostat (stuck open). replace it before it kills your cat.

Well, I do have an OEM thermostat and gasket, and new water outlet O-rings... Hmmm. Hoping for something easier... Thx for responses.

Yes, it sounds very much like a thermostat stuck open.

What does your username mean? Do you have a V8 Quattro?

Not that difficult of a task. I would change it before it blows your water pump seals. Now that is a PITA.

Way back in the day, I was on an Audi V8 BBS, and have used that avater ever since.

Actually replaced the V8 with the Lexus. Not nearly the same capabilities, but the ES300
has been been so reliable, it has allowed me to play with Little British Sports Cars.

Lots to be said for a paid-off reliable old car!

Still miss the V8, but what a complex machine.