Fans staying on long after engine stops ...

[pxl108]

Hi All,

I'm probably overreacting to this, but i've noticed of late that the fans in the engine bay are staying on at what seems a very high speed for long after the engine has stopped. Even on a very short journey, such as to the shop, about 1 mile, and the engine is not even hot at that point, the fans are on and it sounds like a 747 about to take off - i have never noticed this before - is this normal ? - VAG-COM is showing no fault codes ..........maybe i'm just being paranoid, but in the computer world where i work, fans on at full speed on a server generally mean it's in panic mode (cos its lost a sensor) or just very hot ........... Any suggestions as usual gratefully received !

Phil

[raj_patel]

i had this problem last year, turned out that i had to have the thermostat replaced, which effectively means the same as doing the cambelt, as it all has to come off to do.

[Rek]

Same happened to me with the thermostat. The part is £25 approx but the labour to get at it is expensive, unless you are having the cambelt done aswell.

[pxl108]

OMG - this is one more nail in the coffin ...... is this the only thing it could be ?. Warranty company are gonna love me...only just getting DRC done on warranty.

[Rek]

Take the car up to normal working temp and keep it going. If the temp keeps getting hot, until the stop light comes on, then that is my view as it is the same with mine. Other possible culprit for mine at the time was sheared water pump blades, but I thought that would make quite a noise.

Don't worry about the Warranty. You had a bet with them and they lost the bet, thats all! In most cases they win. Thats what insurance is.

[skiwi]

is the engine signalling high temps? you can check with the real-time readouts from vag-com (display group 1, field 2). if so, the usual suspect is the thermostat - don't take the car on long runs with this condition as it will overheat, get it seen to asap. it could be a failure of the high-speed fan controller - there are no diagnostics for this. the engine temps sholud verify this.

[pxl108]

the engine temps never vary, and are both (oil & water) quite low, water never gets above half way, and the oil temp never even reaches the first mark on the left of the guage...........spoke to Grizz last night and he also suggested the fan control module, so i'm just looking into that ....... thanks for the advice guys !

[Lig]

Hi Chaps,

My fan(s) seems to stay on a while when just turned off. however the temp is fine (just sits a tad below halfway). I kind of think this is normal?? I dont think it is worth stripping down just to change the thermostat ££££ if everything else is fine????

If the thermostat was dodgy I am sure it would overheat...my advice is to wait until there is a 'serious' measured problem before shelling out. Because the fans are on an electric temp sensor they will stay on when the engine is hot and just switched off??!!

Lig.

[GardinerG]

Please correct me if I am wrong but isn't the thermostat different to the G2/G62 temp sensor. It would be this that controlled the front fan (via the control unit) not the thermostat whose only job is to divert the flow of coolant between the shorter (warm up) and longer coolant channels? If the fan is on constantly I can't see how it would be the thermostat unless the longer coolant channel was blocked off (and engine running too hot all the time). If the sensors are showing cooler on both the oil/coolant temps then I would assume this is simply cuz the fan is on all the time, which was what you were saying, wasn't it? In which case check G2/62, or as Grizz says the fan control units.

Electric radiator fans -V7 and -V177
Function:

The Audi RS6 is equipped with two electric radiator fans:

◆ Radiator fan 1 -V7 (600 W) on right-hand side seen in direction of travel (with integrated radiator fan control unit -J293)
◆ Radiator fan 2 -V177 (300 W) on left-hand side seen in direction of travel (with separate radiator fan control unit -J671 on left longitudinal member)
Both fans are activated at continuously variable speeds by the engine control unit via the respective radiator fan control unit.

◆ Contact 66 of engine control unit is the control output for radiator fan control unit 1 = 600 W.
◆ Contact 104 of engine control unit is the control output for radiator fan control unit 2 = 300 W.
These criteria are applied for the activation of the respective radiator fan:

◆ Selection of fan by the air conditioning system: the air conditioning operating and display unit transmits its selection to the engine control unit via CAN bus, which forwards it directly to the fan.
◆ Normal engine operation: under normal driving conditions and with engine idling the fans are controlled according to the coolant temperature (above 98 °C) and the ambient temperature.
Radiator fan run-on

During the radiator fan run-on the 300 W fan is activated with a constant on-off ratio of 55 % and the 600 W fan with a constant on-off ratio of 40 %. Three criteria are applied for the triggering of the run-on and the selection of the run-on period (30 to 400 seconds after turning off engine):

◆ Fuel consumption during the previous driving cycle above the set threshold value and engine temperature above 105 °C (when engine is turned off).
◆ Coolant temperature above 105 °C and ambient temperature above 0 °C.
◆ Engine oil temperature above 110 °C.

Oh, and the usual culprit for the jet engine is the AC fan, but this can be rulled out by turning off the AC (pressing "-" until it shows "off" on Solar roof cars), but I doubt this is your prob.

Dunno if that helps.

G

[Lig]

Thanks for this Grant, very helpful!!

From the data I will just do a quick monitor of the fan time, as according to this it can run on for 400 seconds (which is a long time - just over 6 and a half mins and mine never stays on that long)!! Not that I am concerned but very useful info!!

PHIL - I would turn your air con off then - check that your fan(s) arent on at startup or even when getting warm but they kick in when at operating temp - then turn off engine and time the fans before they shut down if it is only a couple of mins then I really wouldnt worry??!! IF they are on at startup then I guess you have a problem?!!

Cheers,
Lig.

[pxl108]

ok - thanks for the info.........i've tested with the AC off, but not timed the run off of the fans.

I'll have another look at it

Cheers All

[skiwi]

as noted above, the fan control circuitry uses one of the (combined) temp sensors in the back of the rhs head. the temp sensors are combined into a single unit, one is used for the display, and the other (g2) for the ecu. as noted by the op, these are giving normal temps, which suggests the fan control circuitry. each fan (600w and 300w) has separate controllers. as noted above, i believe that during "run on" both fans should operate. is this happening in your case? if so, then this is the ecu telling the fan circuits to operate and not a failure in the fan control. if however, only 1 fan is operating, this is likely a fault in that particular fan circuit.

[skiwi]

i've checked up on the ecu's ability to check the performance of the temperature system. my experience of this has been with the motornic 6.3 system in my old s8. the me7.1 in the rs6 is quite a lot more sophisticated than that. it continually tests the engine temp sensor for plausibility, and also the ability of the radiator to reduce engine heat. it seems that it logs the volume of air through the maf's and extrapolates how hot the engine should be after taking into account loading and throttle use. if the engine is colder or hotter than this it concludes that there is an issue and will, in this case throw an mil. clever clots...

[Lig]

Hi Skiwi,

thanks for that, could you just clarify what you are saying at the end of your second post......."if there is an issue and will, in this case throw an mil"??

Cheers,
Lig.

[skiwi]

sorry 'mil' - bosch-speak means that the engine warning light will come on (malfunction indicator light).