95 S6 Losing Coolant, no visible leaks
 

Hi,

I have seen a couple of posts around the web about losing coolant with no oustide sign of a leak, but nothing specific about replacing a head gasket. I do not appear to be burning coolant (no white smoke) but the loss has increased over the past couple of months and I had to replace my oil sending unit recently. I have to put in about 1/2 quart of coolant a week. It only drops level when I run the car.

I am operating under the assumption that I have a head gasket problem, yet I am the original driver of the 192K miles car and it has never overheated. I will be taking it to do a cylinder leak down test, but would like to be prepared for the worst.

So, if it is a head gasket, is this something I can do, or do I need either the dealer or other shop to do it for me. My only other head gasket experience was 30 years ago when I replaced the head gasket of my 77 Honda Accord, and while that went well, a lot has changed since then. I have done suspension work and tuning work over the years, and continue to do various maintenance jobs on the older cars but I am not a mechanic.

If this has been covered in another post (and I have just been too dumb to be able to find it) please direct me there. I love this S6, it is in beautiful shape and I would hate to not save it.

Thanks in advance for any guidance,

Ed

1995 90 Sport Quattro
1995 S6
2008 S6

Previous Car: 1990 CQ (sold it with 335K on it)

Just taking a stab here, and someone with actual knowledge will come along soon - but if there's no obvious leakage and you're not seeing any white smoke - is it possible steam is escaping under pressure while you're driving from somewhere - so its essentially evaporating

Had a pressure test on the coolant system done a couple of months ago when this started (and I was losing much less coolant) they found no leaks at that time.

Ed

Doing any meaningful long distance guesses about your problem is difficult at best, but trying to do this when the person doing the work is not even involved makes it more so. This "pressure test" was done in an attempt to find a coolant leak? Or the usual check to insure the system is maintaining the correct pressure? Because, if you were looking for a leak, a leaking headgasket is still a coolant leak, and if you are losing coolant, you have a leak.

Are you using a coolant that leaves visible traces at a leak (Hint: Audi coolants do this.) And, there are none of these traces anywhere, old or new? And you have investigated all possible areas with a thorough, disciplined approach, using a bright light, and cleaning off any old traces? You need to do all this before resorting to a check for an internal engine leak, then check the spark plugs looking for a steam cleaned plug or two. You would expect that coolant in the combustion chamber would cause some mis-firing to some degree.

The big new item on this engine is the turbo bolted to the exhaust manifold. Removing the head requires either removing some difficult bolts on the exhaust manifold or removing the head with the exhaust manifold and turbo still attached, making it unbalanced and heavy-definitely not a 1 person job, and done better with an engine crane.
Your DIY job is just to R/R the head; a machine shop will do any work required on the head-valve stem seals at least.

Understood. I am less looking for a diagnosis than an opinion whether I can deal with the job. I have another car to drive and a garage where the car can sit while I do the work.

I will check with the dealer to see exactly what kind of "pressure test" they did. I had explained what was happening, so I hope they tested in such a way as to rule out a leak in the cooling system (water pump, lines, radiator, overflow tank, etc) outside of a problem with the head, but I don't know that for sure. Originally the Audi coolant was in use, but I was going through so much of it recently I switched (I know I shouldn't have) to the off the shelf green crap.

The only other clues are a rougher start & idle when cold and a slight pull back when threading the throttle at cruise. The engine still feels strong under heavy throttle and there is no hesitation (like I have experienced when I had to replace a coil pack). The funky running I think would point to coolant in the combustion chamber but there is no white smoke.

The plugs looked normal when I replaced them a week or so ago (along with the fuel & air filter). I think the coolant may be getting directly into the oil. While I didn't see any heavy milky residue, the oil looked off when I replaced the oil sending unit that failed (and maybe it failed due to coolant in the oil?)

If I am not burning any oil, and the compression test is solid, do I want to get the head redone? Do you think having a head redone while the bottom of the engine is original is going to create any issues? It also looks like dealing with the timing belt is no fun task either (always have had the shop do that).

Like I said, I love the car and don't want to give up too easily on it. I would love to see someone's write up on doing a head on these cars (reading a write up on my wife's 90 Sport Quattro EGR Valve helped me deal with cleaning that and the throttle body).

Thanks for the response,

Ed

At 192K miles, I would have the valve guides checked for wear and then lapped if ok and seals replaced at a minimum. R/R of the head can be a good DIY project if you organize even before starting work and maintain control of the workplace. You will want assistance with the head removal and replacement to control alignment, etc. The right machine shop to check the head and do any valve work is the key to success here. Since there are so many things involved, making a progress listing can be helpful in organizing parts ordering and the work flow.

If there are no clues in the combustion chamber/spark plugs for coolant, I would look harder for the leak external to the engine. The pan under the engine can stop some of the spots on the driveway from giving clues. Be sure to look in the plenum chamber behind the firewall. The Bentley workshop manual would be helpful to say the least,but this should help. I don't know of any FAQ that has tackled the entire head R/R proceedure, but there are some sections that may be helpful. Motorgeek may have more on the engine work itself.

http://s2-audi.co.uk/workshop/aan/aan.pdf

http://tinyurl.com/7aeckc3

You're not the only one with coolant leaking now

I've filled up my reservoir 2 days in a row and its empty again -- mine is leaking towards the back of the engine somewhere, my feet were even getting dripped on while driving, with no AC running -- ugh

If you are getting coolant inside the cabin, then it might be your heater core leaking. While I have never done that job, I think it requires removal of the dash & center console, though I do not know much more than that.

Ed

Neither the dash or the center console have to come out for a heater core.

Its gotta be a heater core -- my front drivers floor mat is soaked -- is there any step-by-step for getting a heater core in and out -

this could be my biggest job ever, but I'm ready for it -- the only shop I've ever used here is down to 1 mechanic, and they are swamped -- not a lot of good german auto shops in Charlotte NC for older Audi stuff

Better go dry things out some.