Engine cooling fans

[mannyo]

I believe that the fans for the radiator are multi speed and will vary the speed based on coolant temperature and demand.

I have a feeling that mine maybe running on maximum speed all the time, although I have yet to confirm this.

Yesterday when I started the car after playing with the sunroof we noticed that the radiator fans kicked in very loudly and could easily be heard over the engine. The car had been parked for around an hour without the engine running, and the interior was quiet warm so needed to be cooled by the A/C.

I stopped at Winchester services on the M3 on the way back from Dorset and after returning to the car had a quick play with the climate control. If you engage econ mode from the setup menu (thus disabling the A/C) the fan noise stops and returns when you switch that off.

I gather there are a number of potential causes for the full speed, and I'll slowly check them. perhaps someone can confirm these.

1) One of the two fans has failed, thus the working one is operating harder to compensate
2) The fan speed controller
3) I read something about coils or something like that failing.

Any other reasons?

[eng33]

No specific A8 experience, but generally sounds to me perfectly normal behaviour, if the AC was running the fans would normally run at full speed if the car was stationary.

[ScottD3]

I thought the fans would kick in at full speed if there was a AC error, not if the AC was running correctly?

Any fault codes to do with cooling or the AC?

[tersono]

Probably an entirely different problem, but I recently had radiator fans running at full speed plus (intermittently) a coolant temperature warning light and a non-functional temp gauge. Letting it warm up then stopping and restarting would clear it the fault for a while. Turned out to be a faulty coolant temp sensor. Had that replaced and no issues since.

[ainarssems]

Without checking for details on D3 I can say that it is normal that 1 fan comes on when AC is on as AC radiator needs cooling regardless of what temperature the engine is on. For engine cooling both fans will come on and change speed depending on engine temperature. Older models have 2 or 3 speed steps, newer ones have PWM controlled stepless speed changes.

[mannyo]

I had a look this evening, and the D3 at least in 3.7 form has just one single fan which is a very large one on the NS side of the engine bay. I thought it would have two like the D2 had, but nope only one, the OS side of the engine bay is solid plastic so could only have ever been one.

The fan speed did appear to vary, so maybe all is good after all.

[paulrstaylor]

Mine did this a couple of years ago, had to replace the fan as the controller was integrated as a single part...... wasn't a cheap job from memory as the was quite expensive and fitting required the front end off

[mannyo]

My cooling fan is continuing to run at full speed with no ill effects yet apart from a lot of extra noise which you don't notice when driving along, only standing outside the car when stationary.

I've been reading about a thermal sensor in the radiator that triggers the different speeds, any idea where its located so I can run a few checks?.

[mattylondon]

I've read they are on the right side, and there are two on v8's, one for the fans, and one for the gauge.

[ainarssems]

Check the temperature in VCDS is normal and no error codes regarding temp sensors. It could be fan speed control unit shorted. Unfortunately I think there are no aftermarket units available and dealer does not sell unit on it's own, only together with a new fan at a cost of ~ £460.