tester123

While the Banks 1 & 2 running lean is still a standing issue, another one needs attention...

Engine is overheating in hot summer days (esp. with A/C on) in standing traffic. End up turning off the A/C and roast in the heat many times

Last year, the coolant level in the reservoir keeps going low and after long drive and parking, could smell there was some "burnt" smell (can't say if it is coolant or plastic or mixed). Visual checks indicated NO leaks, and reservoir or other components are not deformed due to heat. So, kept filling to maintain levels and went through a whole container bought from dealer. On to the second one now. (could this stuff be boiling and evaporating???)

Some how nowadays, the coolant level is holding up fine. Still, the car's temp goes over a notch or two (if I didn't pay attention) and the oil temp is also moving a notch up. Things come back to normal after traffic eases and driving back to highway speeds. Obviously, insufficient cooling is the case.

No work has been done (i.e. radiator flush etc.) to think there is air in the system. I read that the "Viscous" fan could be going bad and this is a symptom...? Read a bit about this fan and not sure for now. The fan spins with the engine fine. Don't know how to test it to see if it is working properly.

Coolant fan does come on when the A/C is on but, Did not confirm independent operation (i.e. due to temp increase). No other components on the engine cooling side have been changed thus far.

Any insights? (Thanks for reading the long post!)

Kris Hansen

Have you done the timing belt/waterpump/thermostat service yet? The coolant could be boiling out, especially if it's actually overheating. Or, it could be leaking. If it was my car, I'd certainly have a look at the water pump.

tester123

No, none of that has been completed but will be in near future. I am thinking of the kit from Blauparts (along with their tool rental). Is there a better option? If so, what would you recommend?

willywacken

That definitely sounds like a not working thermostat to me. It occurs every now and then with the V8s and V6...

Does the engine cooler get hot or only warm? Does the oil temperature rise to similar values as the coolant temperature?

Just Me

If it only overheats under periods of hgih thermal stress, your T-stat must be opening.

But it also suggests you have either:

1. low flow
2. low heat exchange at the radiator

Low flow could be many things, partially opening t-stat; h20 pump; clogs

Have you measured coolant temps at various points?

G

Just Me

yes, t-stats are an issue. But how does it sound like a stuck t-stat? If the t-stat sticks, the car overheats under all circumstances - and pretty darn fast. Unless it sticks open, and then it wont warm up.

G

willywacken

No, an closed thermostat doesn´t automatically lead to overheating. This highly depends on the driving speed and the performance, that is demanded by the driver. I already had some engines, only overheating within the city. Riding the highways was no problem at all.
But to be sure the G62 (coolant temperature sensor) should be checked, too. They tend to break over the years, often resluting in an intermittent error (short to plus).

Just Me

Oh, yes. On a C5 Audi, a T-stat stuck closed will overheat a moderately driven car, even in the winter, in a matter of a couple miles, from dead, stone, cold.

Else, its not closed. Its just not fully open.

G

willywacken

Well I see where you´re going, but I´ve already had my hands on several C5s, it´s not always that dramatic. Wait, there are no Diesel-versions of the C5 in the US, right? In that case, forget about my moderate-driving-statement

Just Me

Its just that simple - a closed t-stat allows no water to flow, by definition. The water jacket will warm, then exceed design spec. Simple.

I've seen it several times. I cant go 3 miles - creeping- trying to get to a shop.

If you can drive it under light load, what you have is a partially open t-stat, or a water pump problem. Maybe in the end the same replacement procedure, but quite a different situation - if for no other reason than you are NOT dead on the side of the road.

G