N2AK

As the original owner of a conscientiously dealer-maintained 2005 A8, w/ 140,000 mi. I have resigned myself to the fact that I have a rare leaking head gasket. It won't start here, in Anchorage, in cold weather. Jordan, the mechanic I trust, says that because there's coolant on the cylinder walls that when- on cold starts-more gas is sprayed in the cylinder the coolant keeps it from starting. He says to park it in the garage (hey, the A5 convertible had dibs) & to release the cap on the expansion tank so that there is less pressure in the system. And so I throw myself at your tender mercies. Does this make sense? I'm having trouble wrapping my head around trashing an otherwise beautiful car. Then again, moving to Florida seems a bit extreme. And selling the car w/ the caveat, "Oh, by the way, it doesn't start in cold weather" doesn't appear to be the best marketing technique. The weird thing is that, yes, it puffs smoke when it starts but there is no oil in the coolant & the dipstick has no foam & the coolant reservoir doesn't leak- although coolant does. Could Jordan be wrong?

target39

The cheapest and easiest way to verify if you have water/coolant ingress into the combustion chamber is to inspect each cylinder and piston head via the spark plug hole with a borescope camera. At 140,000mi, there should be a decent amount of carbon buildup, but if you find a cylinder or two to be cleaner than expected, water/coolant has gotten into it.

That being said, Jordan's theory doesn't add up, at least the way you described it. If coolant was getting into the cylinder walls (combustion chamber) because of a bad head gasket and coolant pressure, it would cause much worse issues than a no-start condition. In fact, you would almost immediately hydro-lock the engine and bend some valves just by cranking it with the starter as it is an interference, high-compression ratio engine.

An important thing to note is whether or not this is a no-crank (starter won't engage and/or spin crankshaft) or an actual no-start (starter cranks engine, but engine won't combust).

I'm assuming this is an actual no-start condition, and since it only happens in cold weather, I'm going to assume it has to do with fuel trims/supply. Similar to small engines in snow blowers needing to be choked to start in cold weather, these engines need the proper ratio of fuel and air to start the combustion process, especially in the cold. Basically, I'm assuming that your head gasket is fine and that the coolant is not entering the combustion chamber since your engine is not destroyed yet and oil/coolant have not mixed. Puffing smoke at start is normal in the cold, as long as the smoke does not smell like "sweet" coolant or smoke excessively. Last, but not least, head gasket failure is rare on these engines, let alone a well-maintained one at 140,000mi, regardless of weather (unless you've been experiencing -100°F or something).

Finally, what do you mean by: "the coolant reservoir doesn't leak- although coolant does"?

mishar

Jordan is wrong. If you have coolant in a cylinder when you start the engine you would have enormous amount of gases in your cooling system, extensive bubbling in your coolant reservoir and your heating will stop working. Next could be hydro lock and possibly broken connecting rod (not valves).

As always VCDS scan will help. Too lean mixture, to old spark plugs, badly clogged fuel filter, bad fuel pumps, clogged injectors are just some of possible faults. You need a good mechanic. Not sure that Jordan qualifies as one.

MP4.2+6.0

Agreed in general w/ other responses. And I have the question about what is going on as far as coolant loss. Also, when you say no start, you mean like never? Or you mean, difficult/prolonged start?

Among other things, besides the further diagnostics I would run a couple of bottles of Techron through it regardless over next few tanks of gas as just good remedial practice on an older one w maybe some issues. Otherwise,I will await more info before providing other ideas.

N2AK

Thanks for the thoughtful replies. To answer your questions: as the ambient temp dips the engine gradually becomes more difficult to start- so that it will always try to start but doesn't "catch" & run. And as the outside temp cools it noticeably runs rough for a few seconds until it runs smoothly. And, Mishar, Jordan works for the Audi dealer so I can only assume that he is using diagnostics to run codes. And the beast will definitely start immediately when it's parked in our garage. And no coolant on the floor. I thought a block heater might do the trick but Audi doesn't sell or install block heaters. (Maybe I should just replace the coolant with Barrs Leaks- just kidding.) I can handle if it's a head gasket & I can only start it warm. The only reason I'm being so stubborn is that I'm not convinced that it's been correctly diagnosed.

N2AK

Also, the heater is great, no bubbles in the coolant reservoir &, yes, I 'll start Techron .

MP4.2+6.0

1. Does the coolant level drop in the reservoir? As in, do you have to add some periodically? If so, has the belly pan been taken off and everything thoroughly inspected for leaks?

2. Have you tried to start it with Ether (starting fluid spray) in the extreme cold scenario? If not, I would and then report back. Can help get at whether it is electrical/ignition vs. fuel.

A hunch here is if there is a coolant loss, it is a physical leak (not head gasket), and then it is coupled to something else but unrelated--weak fuel pump, failing crank sensor, etc.

N2AK

MP4.2 I appreciate your tenacity. Yes, I lose about a cup of coolant every thousand miles. But why would I drop my- I mean the car's- belly pan? What could that reveal? And, I sort of got the feeling from Audi that the mechanic was trying to spare me needless expense by trying to trace down a problem (time= $$$). Maybe, as Mishar mentioned, I should begin looking elsewhere for the problem. But, if something he mentioned (like a weak fuel pump) wouldn't it show itself on a code? And, yes, I've read that this car has become the province of DIY guys but I've worked through most of the D3 gremlins & I just want this A8 to whistle past the graveyard a few more times.

N2AK

I also have a hunch that this IS NOT a coolant leak caused by faulty head gasket. And my friends- 2 mechanics who worked in an analog world of Peugeots, MG's & Saabs, have the same hunch. That's why I really appreciate your advice.

MP4.2+6.0

You drop the belly pan to look for leaks underneath. Simple as liquids flow...down. The pan itself is a very useful diagnostic from personal experience on many an Audi. It allows you to look for any signs of fluids landing on it that may have been going on for a long time and many miles, and then figure out more or less the location. No different than if you had no belly pan and it hit the pavement you always park on, but here it is like you always parked within 1/8" of the same spot every time. The coolant also leaves a characteristic pinkish chalky residue so can be further spotted that way.

BTW, honestly, if neither you want to drop pan and/or mechanic never did it, sell the car since it certainly takes that level of diagnostic, plus fire the mechanic for basic lameness. Pardon my French, but that's basic diagnostics really to give car a thorough look see in light of coolant loss, and about 100x earlier and more likely than jumping to a relatively far fetched conclusion about a head gasket on a motor with almost no history of head gasket issues. And with maybe no diagnostics behind that beyond hunches, old wives tales, or he once heard of it on my 73 100LS lemon or who knows what.

You would also be looking specifically at some things like any signs of leaks or weeping at radiator lower edge, any signs of issues with lower hoses, any issue with the little plastic pipe in the oil cooler area (search on it--a recurring pain in butt 4.2 issue as they get older), etc.

So,

1. You should track down leak. Any leak is not good or normal for a well maintained car, and some like bad radiators, weak hoses or the oil cooler related pipe can leave you stranded in some godforsaken place and paying extra $$ if they let go at wrong time...say like, Alaska.

2. Use any info on finding a leak to shoot the idea it is head gasket in the head, said bluntly.

3. Then go on to find start related issue. Yes, could be fuel pumps. Again, get a can of starter fluid (ether) spray it into intake on next cold start struggle. If it kicks in quickly, it is then pretty likely a fuel issue. For example, the fuel pumps. If it doesn't do anything, it is most likely ignition side issue, for example the crank sensor. Neither is worth selling a car over and taking a further bath just because it has a material issue that can be figured out with available decent diagnostics, sometimes old school, often (but not always) VCDS code scan. If you resolve it and feel over your head longer term, sure sell it at that point as a reasonably running vehicle.