BoostFrenzy

It all started with the gauge not reading 1/2 and the heat not being hot, no big deal... swapped out the thermostat, properly bled the air etc... all was well, gauge on cluster shows 1/2, will work it's way up to the tick past half if you idle long enough at which point the electric fan will come on...

but, then i decided to fire up vag-com and see what it thought the coolant temps were, to my surprise it didn't agree too much with the guage :/ Cruising down the highway @80mph with the gauge at middle, vag-com was reporting 99-102c! Now this just can't be, I also checked the climate control serivce menu 49c reports the same as vag-com and 51c is usually just stuck at 90...

Is it really too hot, is the ECT just bad? I also purged the air again for fun and squeezed the lower rad hose near the housing, not too much resistance and it wasn't really hot, i think the t-stat is opening properly.

I also unplugged the ECT to take note both the cluster gauge and ecu data are lost for coolant temp, is it possible the ecu side of my ect is bad? Also, when the fan switch activates the electric fan the ecu thinks it's more like 110-112c than the 100ish c that should be turning it on, basically everything in the car agrees with the water temp except for the ecu-side of the ect?

Carson (K03x2)

located on the radiator. It turns on the fans independently of the ECU. It could be the cause of your fan issue, wouldn'y be the first time I have seen one go bad.

AudiMick

Because logically that would mean both the gauge and ECT are bad.

Has anyone else checked this reading with a Vag.com on a different car?

BoostFrenzy

the fan activates where it should on the gauge, but vag-com always hovers 99-103c*

Reggie

Doesn't the sensor have two outputs - one for the gauge and one for the ECU

BoostFrenzy

yes, it does... i'm wondering if the ecu-side of it is faulty

Reggie

On my 98 I think there is just one. I replaced it because the gauge side failed. Was a mf to get the new one in - very tight contortions needed for the hand. Not sure about the 1.8T

BoostFrenzy

98-99c @ 75mph cruise w/ 70f ambient temp, maybe I need to bleed again... i understand the heater hose needs released so the hole is exposed, this is done with the engine running cold until tstat opens and expansion tank raised with cap off correct?

BoostFrenzy

didn't make any difference still :/

BoostFrenzy

put it in diagnostic mode by pressing & holding recirc and then press the upper vent button above center vent, it will display 1c, press temp + until you see 49c or 51c, then press recirc again (will show values for both, on my car 49c is the coolant temp, i've heard it's 51c on others)... let me know how it does @ idle and while cruising around

thanks a ton