engine suddenly running hot...

[woobanger]

I had a very alarming ride home today during which the oil temp. reached 110 degrees C and the coolant temp reached upwards of 100 degrees C, which is +20 and +10 above normal, respectively.

The oil temp had been a slightly higher than usual in the past few weeks (100+), which I attributed to the need for an oil change. I checked the oil level a few days ago and topped up maybe half a litre or so with a different oil (Motul 300V 10W-40) than what I had in (Wakos 5W-40). Could this be the reason?

I didn't drive the car hard today, just running errands in the city, the ambient temp was pretty cool, 10C or so, so I'm not sure what caused this suddent heat issue. The coolant level was normal when I checked under the hood.

It's one thing when the oil is running a bit hot, but it was alarming to see the coolant temp go up. It never seems to move from the centre 90 mark even in the hardest driving conditions.

I'll take the car in to the shop first thing next week, but any peer diagnosis in the meantime would be appreciated.

Thanks in advance.

[jonas21]

I wouldnt be too scared by this, oil can go north of 130 without any problems.
Regarding the coolant...thats another story. Some people say that on relativly new cars the coolant display is kinda fixed to 90 so it wont ever go north of that. I personally never had more than 90 degree. However i'd be very careful when you see the coolant at 100 and it still increases at normal driving. Thats usually a sign of a problem somewhere. I've seen cases where small stones or other waste on the streets did drill holes into the cooler behind the grill. Usually coolant fluid drain can then be spotted below the car.

[skiwi]

the usual fault is the coolant temp sensor, but it could also be a sticky thermostat. there is little in changing the former, the later is a pain.

btw, the coolant temp sensor has 2 circuits, one to the instrument cluster, the other to the ecu. the instrument cluster controller "pegs" the temp @90C until the variance is upwards of 10C. this stops the punters complaining of small temp variations...

[Aronis]

Arrgggg, you're not using the RS6 specific engine oil!!!!!!!!!!!!!!! YIKES>...warrantee void......

Check the cooling coils for road salt/sand buildup. My car was running a bit hot after the second winter due to the coils (engine oil cooling coils) being covered with road salt/sand. After cleaning them (done by dealer with hight pressure washer) the car's temp was about 20 degrees cooler...

Mike

PS change the oil back to the magic mix.

[woobanger]

Thanks for the prompt replies.

I've got an S6, not an RS, and it's now beyond the warranty period.
Regardless, the Wakos 5W-40 is listed in the VAG list of approved oils.

BTW, where are the engine oil cooling coils located?

How tricky is it to fix/replace the theromostat? The local Audi service is booked out for the week, so I'm considering taking it to my mechanic instead.

[skiwi]

the procedure for replacing the thermostat is the same for the s8 and the s6. the toothed belt has to be removed. this is a job for the dealer, believe me...

on the normal v8, the job is a piece of cake (no need to remove the cambelt) so it pays not to get confused (or, more particulalry, have your shop get confused)...

[woobanger]

Drove the car briefly this morning and the strange thing is that the coolant temp rises to 100C+ and then drops back to 90C, then shortly thereafter rises back up to 100C+. This was the pattern I noticed over the weekend. Another observation was that the temp reaches the 90C norm noticeably faster than it usually does.

Took the car in to my mechanic and his diagnosis was a faulty "fan clutch"? which told me was the little device attached to the fan behind the radiator, which controls the speed of the fan, depending on engine operation/heat. He based it on the fact that the fan would not accelerate when the engined was revved 4000+ RPMs like it should.

I left the car and asked him to call me first thing in the morning after he sourced the part, to decide a way forward.

Your thoughts??

BTW, the car is C5 S6...the V8...

[skiwi]

given the fact that the temp is "cycling", i think your mechanic is on the money....