Is my Audi A4 head cracked? What to do?, Last update. 10/13. Spewing coolant. Options

[jk76.914]

I may be in a pickle. My daughter's 2004 Audi A4 1.8T, 105,000 miles, was using some coolant. I looked and looked and looked, there was no evidence of a leak. It used about a pint every 500-1000 miles, so I thought there should be some visible sign, but no. There's no symptom at all. Nothing wet, driveway dry, no smoke, starts good, runs fine....

But then yesterday, after topping it off again, I changed the plugs. The threads on the #4 plug were wet. The other three not. I'm guessing a crack from the plug to the water jacket somehow, and it probably opens up at temperature, seeping coolant into the combustion chamber.

What do you guy's think? The wet threads seem to confirm the diagnosis... Any other ideas? Anybody know if these things are prone to cracking?

Any danger in trying a Bars Leaks sealant? They're pretty well regarded, I think, and they have four products for cracks, head gaskets, etc... I'm thinking of trying the mildest first.

She commutes from Boston to Rhode Island daily, putting about 400 miles on the car every week.

Here's a picture of the 5 valve combustion chamber I found on line. Lots of opportunities here for cracks... Help!

[jk76.914]

OK, I'm home

I made it to EMS and met Mike. First of all, he sends his regards, Rich. He's a very knowledgeable guy, and we went out to the A4 to have a look. We could smell coolant as we walked up to it, and that's the first good news, I guess- it's gotten worse, so it should be easier to diagnose. He looked around under the hood while I told him my tale. He also couldn't see anywhere it's obviously leaking, but he said he'd take it in and pull all the plugs and do a leak test and find the problem.

We walked around and looked at his used car inventory- very impressive! A friend of mine came along with me, and he may return and buy a 2006 A6-4.2 with 25,000 miles that Mike has...

So about then we walked back to the A4, and there was a small pool forming from the AC condensate, and Mike said, "wait a minute. Back the car up." So I did and there was a second puddle, about 6" across and centered under the back of the engine. It was coolant.

So neither of us can make a connection between the wet threads and the leak, but I got to thinking about my story, and I remembered that I was remembering it wrong. It wasn't after the timing belt change, in January, that my daughter was driving to New Jersey. It was July, and she was driving to New Jersey after the dash of the car had been torn down at the local Audi dealer to extract the carcass of either a chipmunk or a flying squirrel who had moved into the heating system through the cabin air filter, and then died there. Now I'm thinking they monged up the heater core, or didn't tighten a clamp or something. Now that I'm smelling coolant inside the car, and now that a puddle has seen fit to form under the car. Still can't connect to the plug threads, but I'm dropping the car off to Mike on Tuesday, and I'll report back.

Thanks everybody, for the interest, advice, and reference (Rich). Mike also does insurance appraisals, and I still need my 914 appraised for my new insurance company. So that'll be next.

Here's the car my buddy looked at-

[rohar]

Still can't connect to the plug threads, but I'm dropping the car off to Mike on Tuesday, and I'll report back.

Believe it or not, things are making more sense. The 1.8t (and most VAG engines) are very sensitive to cooling system leaks. With the advent of more and more plastic parts, this seems to be popping up more often but the problems go all the way back to the old 1.6l engines. If there's a minuscule leak, even so small only gasses escape, the system can't pressurize properly. Under pressure, the coolant cannot turn to a gas at higher temperatures. When the pressure is relieved, gasses can form almost anywhere in the system and create hot spots while the overall temperature of the coolant seems normal. Since the head is the highest point in the system, that's where the hot spots generally occur. This can cause cracking in the head but normally it's just warpage.

On a somewhat related note, I've run across any number of people who are pissed that VW switched to plastic water pump impellers as they tend to go out early and often. On every one I've come across, there was a leak somewhere else in the system. Most often, a worn overflow tank cap.