mcano

My car over heated on a canyon drive. After having my car towed home, I began checking the cooling system for leaks.

After filling the coolant tank back up to the maximum level (the coolant level was low due the discharge of coolant when the car overheated), I started the engine and ran the car in park for about 10 minutes. During this time I did not see any leaks in the coolant system. However, after the temperature gauge reach the normal operating temperature, I noticed that the radiator fans did not come on. Is this normal, or is this the likely cause of my over heating?

I bought an Audi 2009 S6 Repair Manual and they show a Coolant Fan Control (FC) Control Module J293 as part of the cooling system. Is it possible that this control module is defective and not turning on the fans when they are needed?

Any help on this matter is welcome.

Thanks!

PS: is the radiator thermostat another possible cause for my over heating?

kelisko

There are six things to consider here: the driving conditions, the coolant, the fan, the radiator, the thermostat and the water pump. It would be easy for your car to overheat in a hot Canyon if one or more of these five components were malfunctioning.

The heat is transmitted from your engine to the coolant which passes through the radiator. The fan starts up and blows the radiator to dissipate the heat when the thermostat detects too much heat in the coolant. The water pump pumps the coolant through the whole system.

You said after 10 minutes of running the car in park, the gauge reached the normal operating temperature but the fan did not start. This can be normal as the fan will normally start only when the gauge tends to go over the normal limit. To check the integrity of your fan, I would suggest you drive the car around, hard, after warming it up. As you see the gauge passing that normal middle mark, pull over and check whether the fan started operating.

If the fan did not start, either your fan is defective or there is an issue with the thermostat, the water pump or the radiator.

If the fan started as expected, you need to check the pH of your coolant.

Concentrate coolant works best in cold weather to avoid freezing. Diluted coolant works best in hot weather. But too diluted coolant would boil and overflow. You said "the coolant level was low due the discharge of coolant when the car overheated". Did it overflow by itself or did you take the coolant reservoir cap off while it was hot and boiling?

PS. During testing, when your car starts overheating while you are away, after quickly checking what you needed to check under the hood, stop the car, let it cool down before starting it again but drive back home slowly in D mode with the A/C turned off to avoid fast overheating.

mcano

Thanks for your detailed assessment and recommendations.

The coolant discharged by itself when the car overheated. I did not touch any part.

I have been using the G12 coolant recommended by Audi at full strength.

The first thing I'm going to do is drive the car hard enough to get it to raise the coolant temperature above normal to see if the fan comes on. In the past I ended getting the coolant to boil, but I'll try not to get that point during my testing if possible.

I mentioned in my original post about the fan controller. You made no mention of this part. Do I need not worry about this part in the equation?

Something I forgot to mention, was that the temperature gauge was in the middle range position when the overheating idiot light came on. You would think that the temperature gauge would be elevated when the car is overheating. What do you make of this?

I’ll report back after I conduct the test!

Thanks again!

kelisko

I don't know much about the fan control module but it is obviously a component of the fan that could fail as well.

You said you've been using the G12 coolant at full strength. This may be the cause your issue. The coolant may be too concentrate for your weather condition. If a coolant is too concentrate, the heat won't be passed over to it by the engine easily which results in the engine overheating while your gauge says the coolant temperature is fine. This may explain what you said:
I would recommend you use a 50/50 mix of the G12 and distilled water and see if it fixes your issue. Also don't fill your reservoir to the max. Leave it between the min and the max marks.

haloguy628

The G12 needs to be dilluted with distilled water at 1:1 ratio. Full strength g12 does not have the cooling capacity to keep the engine within cooling parameters.

In your case the overheating may possibly be caused also by not properly sealing of the overflow tank cap. Once the engine gets in operating range and the cooling system pressurizes the cap on the overflow tank starts to leak coolant. You can usually see it when you park the car after driving. Once the engine stops and the coolant stops to circulate, the pressure in cooling system goes up and you can see the fluid leaking from the overflow reservoir. If you don't catch it and the belly pan contains the leaking coolant you may end up with underfilled coolant which may also cause overheating. I had this happen twice. Once on my old B5 Passat and once on my S6. You can get the gasket by itself so don't buy new cap.

The coolant temperature gauge is a dummy gauge. It will stay on the 180* mark and not move in 99% of the time. The exception is when your thermostat is stuck open in winter then it stays at 0* because the engine does not reach operating temperature due to the cold, or pegs at max if the engine is overheating.