marcika8001

Hi guys,

So, please help.
There will be multiple problems in this post, but I want to go one by one later.
The car is a 07 S6, 5.2 V10. 205 000 km mileage.

There are multiple symptons with the engine, I believe they are not related to each other, but I might be wrong.
So, the most annoying one first.
1. The cooling fan, (the big one) is always almost ON. You know, the loud one, which gives a sound of the engine, like an F35 fighter at take off. This is the one which really disturbs me.
The temperature gauge on the dash stays at 90C, and as the car warms up, it's pretty normal. (if there is cold outside, it heats up way slower, sometimes it takes 10-12 minutes of slow driving)
The coolant in the reservoir tank is between MIN and MAX halfway. It heats up, so it seems, the coolant is flowing there. Also, the radiators are warm/hot, so it seems, they also have circulation. This thing happens every time, doesn't matter if it's relatively cold (10 C degrees or 28 C degrees outside). If I shut the car down, the fans turn off, they don't stay on after that. The coolant level is steady and the coolant is clean, I don't lose it, so probably there is no leak. Any idea for this?
The fuse box, where are the relays (the big 60A ones) were full of rain water...and this problem started on a rainy day.

2. Sometimes, the idle is rough after start, when the engine is not warm, but also not cold. (I mean serious misfires here), but as soon as I push the accelerator pedal, it goes away and it runs very, very smoothly after that. Under acceleration, (heavy ones) I don't notice any misfire, or power loss. It is important, that the intake flaps were removed of this car, so I'd say, it relates to that. (also, the car didn't have any carbon build up removal, and I have a feeling, I have it) It gives CEL light too (sometimes flashing one), which says misfires.

3. Also an annoying and a very tricky one. After a start, and about 10 minutes of driving (on the same route it happened on same place 5-7 times), when I start to roll from stop position, the car loses (seriously) power for 2-3 sec. If I don't push the pedal, it can even stall. If it stalls, I crank it, it starts immediately and runs smooth for hundreds of kilometers. A couple of days ago, a stall happened at a railroad crossing, I have to say, I almost pee under myself. (there is a heavy train traffic there) Fortunatelly a restart solved the problem and I rolled away. But again, this happens only when I start drive from stop, it never happens under load, or driving.

4. A smaller one, but well, I hate these. Sometimes, from the front left of the engine, burning oil smell comes. I had an A8, where the same happened, and it was a broken sealing on the top of the cam houses. I guess, this is similar. Oil is on steady level, and there is absolutely no burnt oil smell from the exhausts.

So, this is it in a nutshell.
The services here in Hungary are terrified of the 5.2 engine, so, it seems, I have to go there with some info, and some suggestions if I want to avoid a HUGE scam.

I really appreciate ANY help or experience guys!

Sverige

You need to be able to scan the car for codes, because the first question anyone on here is going to have for you is “what codes does it have?”

If you don't already have Ross-tech vcds or an x-tool VAG401 then that should be your first step.

marcika8001

Yep, currently, I'm desperately trying to find someone with vcds. It's not as easy as it sounds here.

marcika8001

UPDATE.
We tested it.
For the rough idle, we have a lot of misfires (across ALL cylinders), and (this is what surprised me), we have lean mixture too. (low fuel pressure)
So, probably there is a loooooong way ahead of us. Decarbon, check sparks, ignition coils, injectors. It seems, I'm in a touch someone who is a good mechanic and most of them can be done at once.
That's one thing.

The other thing, (the fan) to be honest is more disturbing. It seems, the engine temp really gets high.We have checked it realtime from 75C. It went up to 90C. And then reached 100C. Then, the fan kicked in on the lower blast. It was going up to 110C, then the fan kicked in on FULL blown. Nothing changed, still going up, and we turned it off at 114C. The car was idling and was parked at a place, where the external temperature was about 17C. We checked the pipes, all of them were hot, and the radiator (at least the upper part of it) was also hot. So, it seems, the coolant is circulating through the engine and the cooling system. There were no any cooling system or fan related error in the memory.
I think, I know the cars, or at least I know, how them works. This is just impossible to happen, if coolant is circulating, the fan is on full speed, and the engine is warming on idling.
The next step, I will do, I will measure the temp of the pipes with laser, to see, if it's really that hot.
If yes, we will do a big cleanup of the whole coolant system, (removing the radiator too) and clean the front of the radiator and lets if it helps.
Our guess, it's that maybe the sensor is bad, and it reads false information. (through this, the temp meter on the dash was steady)
Do you know, (in the service, they didn't know, - 5.2 V10 is not a frequent guest - and we didn't have time to check) where is the sensor physically which is actually responsible for this reading?

OR, if you have any guess, and if you have any other suggestion for this kind of problem, please HELP me!

Thanks in advance guys!

91quattro

For the misfires, I would also look at the valve cover gaskets for leaks. Mine were brittle, and leaking oil into the spark plugs. Also, a LiquiMoly product called Valve Clean helps reduce carbon around the injectors.

For the cooling problem - blocked radiator and thermostat come to mind. With over 200,000 km I would suspect the radiator is not functioning properly. Mine just failed a month ago, at 106,000 miles, the plastic was starting to deteriorate and it began leaking. Audi charges $400 for the radiator here in the US. The mechanic said 10 years or 100,000 miles is about all you can expect from these plastic radiators.

Not sure but I think the temp sensor is buried in there, on the right side of the engine.

hrc4u

post a full vcds scan log?
misfires could be fuel pump/filter and so on....that whould be bigger concern for me anyway....
/H

marcika8001

No, I dont have it. :/
it said low fuel pressure and lean fuel. (beside tons of misfires)

Do you mean it would be a bigger concern than overheating engine? Why? Overheating engine could physically kill the engine, with bad pumps, it stops in the worst case. Filter has been replaced 300 kms ago.

We will defintelly check the radiator first. Tomorrow I will measure the real temp of the pipes and radiator. Lets see if the sensor is right.

marcika8001

Update#2.

The rough idle was caused by a broken rubber pipe which is responsible to lead oil gases (I dont know its English name) and the fresh air from outside, REALLY confused the electronics.

The overheat was caused by the thermostat. It was stuck halfway open.

So, problems solved. ~$850 is gone...