Patient is my (mostly) babied '94 940 Turbo, with almost 200K miles. Cosmetically excellent, mechanically great except for this (major) issue, and my mechanics seem to be lost. I started losing a little coolant on longer (over an hour) drives at highway speeds, and, at the same time, getting a little milky oil around the o-rings at the top of the dipstick, and sometimes some very,very tiny bubbles in the coolant expansion tank. However, there's no coolant loss or any other symptoms just running around town (L.A. - across town is an hour plus, sometimes).
So, I took the car into my mechanics, who conducted a "block test" on the engine (the indicator fluid which screws onto the cooling system), which was negative for leaks. However, I still knew something wasn't right, so I sent a sample of used oil off for analysis, which showed coolant residue in the oil, but no moisture (it had all cooked off). So, I took the car back, and off with her head! They replaced the headgasket, and sent the head off to the machine shop, who cleaned, pressure-tested, and resurfaced the head - finding no cracks or defects.
So, a couple of days after I got the car back (made sure the cooling system was fully "burped", I took it for a run up the I-5, 4000 feet up in the mountains and back, about 100 miles. I lost about 8 oz. of coolant, and still the milky deposit around the top of the dipstick. My mechanics are at a loss as to how to isolate this small crack, or leak, which only opens up at high temps. Does anyone have any good ideas how to isolate this? They inspected the cylinder bores and the deck while the head was off, and didn't see anything other than some heavier-than-normal carbon in cyl. #4. Could a machine shop have missed a small crack in the head? Usually, cracks close up when heated, I know...
I'd just like to figure out some good way of finding out if it's the head, the block, or the turbo.... If I had a garage, or even my own driveway, I'd consider swapping heads, and maybe even finding a good used engine, but I don't think my apartment complex would really appreciate me doing repairs like that in the parking lot. I really love driving this car, and it's been ultra-reliable and is pretty easy to repair most things on it. I probably _could_ find another used 900 (pref. a wagon), but I really don't want to go from a car that I know has been well-maintained to an unknown quantity, especially considering that I don't really have _lots_ of free $$$ to throw at another vehicle right now.
Thanks all!