Hey there Jim…
I’ve been lurking around here looking at postings from time to time, but between being sick for a few weeks and being really busy trying to catch up on some projects, I haven’t really had time to participate in the forum during the last few months.
I’m not quite sure how the ambient temperatures would affect the leakage, such as you have observed. However, a word of caution: when I first noticed the residual pressure symptoms I did the same test (letting out the pressure & then starting it up to see if pressure built up quickly). The pressure did NOT build up immediately. At that time, I was not losing any coolant, or misfiring &smoking excessively at startup either. I now believe that it took higher peak cylinder pressures (running at load) to force gasses around/past the gasket. In other words, I wish that I could alleviate your concerns about your car, but I cannot.
It seems logical that you may be at the early stage of head gasket failure, such as where I was at a few months ago. This may explain why the residual pressure problem is not (yet) consistent on your car. I think that it would be prudent to take preventative measures now. I believe that while I was continuing to run the engine, the combustion gasses pushed the water out of the cylinder head passages – this allowed certain localized areas of the head to become overheated, which then lead to the cracking. This is conjecture on my part, but again, it seems quite logical.
So it seems that if you were to pull the head now, it is less likely that it is cracked, but if you continue to run it, who knows….
Another problem that I did not mention in my previous post – while the engine was ingesting small amounts of water & burning it, the resulting steam eroded the upper section of the cylinder liner on the rear of #5 cylinder. The steam ate away about 1/4 of the thickness of the liner at the very top (vertical surface only - the top of the block is fine). There is evidence of similar damage in a couple of other cylinders, but not nearly as bad. The steam also ate away at the vertical edges of the aluminum sealing ring that is integral with the head gasket, so when it was removed, it seemed as if there were two separate rings – one on each side of the gasket, rather than one piece wrapping from one face to the other.
The head gasket overlaps the liner area quite a bit, so I am crossing my fingers that it will seal effectively enough for me to get at least another 100,000 miles out of her. The corroded area is well above the point where there is any ring contact, so at least that is not an issue. I just finished chasing out the head bolt holes tonight – I called it quits when I got to looking at how to get out the pivot point bolt that holds the banana (tensioner) rail in place. It is a press fit, but the mickey-mouse puller I made for the smaller type pins (used on the upper guide, as well as on the V-8s) won’t work on this big one. This plus I have to figure out how to jury-rig something to press the front crank seal into place… lots of work to do…I just hope that Murphy isn’t hanging around to ‘assist’ me…