PMrider

I am running about 1 tick hot (it's been 100+ for the last 2 weeks in TX) and my radiator fans are not kicking on unless my A/C is in recirc mode. HVAC readout climbs nicely and hangs out around 95-96 degrees (centered to slightly right on gauge) in normal driving. However it seems to spike to 100-102 when I slow down. I saw a peak of 107 a couple minutes after I turned the car off today (no fans running but turbo timer pump does). VAG/COM pulls no codes.

1. Would I be running a little hotter than normal because I recently put 1 range colder plugs in? (pulling more heat off the block?)
2. Would the fan issue be the coolant fan control module on the radiator?
3. Why would the a/c turn the fans on but not a hot coolant temp? (I looked through the electrical diagrams but I sucked in my one EE class).
4. Are there any fuses or relays that I can check? (trying to avoid pulling the radiator for the fan control module)

I have a green top coolant sensor, and the thermostat and water pump were replaced with timing belt 15k ago. (BTW got my extended warranty in the mail today for the TB!!)

Any help would be appreciated.

MarTT

Did I read this same post a few days ago?

InTTruder

1. Would I be running a little hotter than normal because I recently put 1 range colder plugs in? (pulling more heat off the block?)
No, since heat flows from hot to cold (thermo rules) the plugs are STILL hotter than the block. The problem is not heat input, it is heat removal.

2. Would the fan issue be the coolant fan control module on the radiator?
Could be, or the thermistor on the radiator shroud. IF both fans run, it ain't the fans.

3. Why would the a/c turn the fans on but not a hot coolant temp? (I looked through the electrical diagrams but I sucked in my one EE class).
Two actuations of fans: hi temp and AC on. Parallel (Kirchoff's law) circuits, not series.

4. Are there any fuses or relays that I can check? (trying to avoid pulling the radiator for the fan control module)
Look at the fuses under the battery cover, the big links that is. Look at your fuse panel, but it is most likely something in the control circuit, not a power problem since they DO run under certain conditions.

PMrider

Straight and to the point. Thanks!

The Chad (VaultPSU)

I've posted this problem before. On my old TT, I had a similar problem. Luckily it was under CPO warranty.

Audi replaced the whole coolant system minus the radiator, they replaced the timing belt and water pump, all fan control modules, etc. Problem still occured and finally they removed and measured the head to find it was warped.

Almost $7k later (Audi's price), and with a new head, the car ran great with no overheating issues (Miami 95 degree sun).

Good luck with sourcing the issue!

PMrider

Yes - I made a similar post but received no responses. Figured I'd try again.

PracTTical

if you remember my cooling saga, i would be running hot and running ridiculously hot during the stopped periods.. one of my fans ended up being unplugged and a bunch of green cheese was on the connectors (corrosion) this hinted at some sort of open drain, causing my cooling telemetry to malfunction. I noticed that the small fan wouldn't turn on after, i'm betting that switching the thermal switch on the radiator will fix that, because AC and hot temps brings both fans on.


plugging back in the fan fixed my telemetry issue, FYI.


i run a tick hot at idle, center while driving.. replace the thermal switch (18 dollar part) and you can easily install yourself, just wear eye protection for all that G12 ;-)

PMrider

Hmmm...That doesn't sound promising...

PMrider

The switch is what I have been leaning towards, but wanted to get 2nd and 3rd opinions before dropping the radiator. I really don't see room enough to R2 while in place.

kappa-q

Which parts are you thinking of removing and replacing? I am chasing similar hot behavior. You can R&R the fan thermo switch from underneath, need to remove the cross over pipe and the driver side plastic skirt (belly pan connects to it). Unplug and move the fan connectors out of the way, and you can get back in there. Actually I had more difficulty removing the electrical connector from the switch, than getting the switch out and putting the new one in.

If you need to replace the fan control module, I think you can do that similarly, but it may involve removing the battery/box/tray to get down in there. I haven't gone there yet, but I may eventually.