Likely Cracked Head -- A Few ?s

[bustedbenz]

Alright, so I'm going to start out with the synopsis of my last few odd weeks, and then finish with a couple assorted questions that I could use a few answers to.

My first symptom showed up a few weeks ago. I was driving along and noticed a low coolant light. Before I could even get off the road to check the level, the light went out again. I opened the hood and the coolant was about an inch above the sensor in the expansion tank (Which was formerly full to the "kaltwasserstand" marking just like it's supposed to be). I thought that was odd but didn't want to open a hot system and needed to keep moving, so I just kept driving. I watched the temp like a hawk for the rest of the trip and it never even climbed past 100 at a stop light. (Summer days this time of year are hitting 92, 93 degrees outside.)

I gradually started to realize that my low coolant light symptom was only appearing under hard acceleration or during long freeway runs at relatively high RPM (3200+). That type of circumstances anyway. I'd punch it to get moving on an onramp, the light would come on, and by the time I could get merged out and start worrying about it the light was off again.

This behavior continued until i added coolant (1-3 cups, I'm guessing) to the tank to replace what was lost (to an unknown location; it's not showing up in the oil visibly yet). Now, I can STILL make the coolant in the tank drop from the cold fill line down to about an inch over the sensor for the light just by driving hard on a hot day. When I park in the yard and leave it idling after a hot run, the coolant is down to that level in the tank. When I shut the engine, I get a little bit of it back in the tank from somewhere.

HERE is the unfortunate part. When I open the pressure cap, the level instantly raises another inch or two back to somewhere close to my fill line (although still, for some reason, not quite to it.) The doubly unfortunate part is that from overnight to the next morning, if I leave the system closed - it's definitely holding pressure. The upper hose stays firm and when I open the pressure cap cold the morning after I drive the car, I get a long loud hiss of air under pressure (NOT vacuum) escaping along with a spew of coolant sometimes. Probably just a couple teaspoons launch out the top of the tank once the cap is loose.

I've repeated this about 3 days in a row.

The car has never in my time of ownership been overheated to 120 or above according to the gauge. Ever. It has, however, experienced anywhere from 4 to 6 events caused by two different problems in which the temperature climbed to what I would estimate at 114-118 degrees on the gauge before I was able to arrest the climb. So I'm assuming I could have cracked a head simply by all those temp flexes even though I have never in my life allowed it to hit or exceed 120.

So here's my questions.

1. Does the pressure in the cold overnight system indicate definitively that my head is in fact cracked, no matter how much I thought I wasn't mistreating it? Is there any OTHER place I should look for the reason for my morning pressure and for my disappearing and then reappearing coolant?

2. Where, geographically under the hood, can I read my head casting number, with the engine in place, mounted, everything just as it is when I drive it, to check if it's a #14 or something else, and likewise to check potential donors for their casting number? Is this information visible from a fully installed engine? If so, on what part, behind which other parts, near which widgets, etc, can I find this information?

3. Is it logical that I could have a cracked head, if that is indeed the problem, and have no oil contamination or antifreeze contamination? I know an oil analysis would show the presence of glycol that my eye can't detect, but the oil isn't going foamy, it doesn't look watered down on the dipstick, and I can find no evidence that the antifreeze has entered the crankcase. I can also find absolutely no traces of oil around the expansion tank area. I know a head crack and a head gasket failure are two entirely different things, but I see those symptoms mentioned occasionally in both contexts.

I'm just going to go from here with it. No doubt I'm at least partially to blame for letting it climb to 115 that many times without trying to make a more aggressive diagnosis of the problem, but that's water over the dam at this point. I'll worry about how it happened once I've got something else to work with, but for the moment, I'm more interested in what to do next. I've got no job this summer so I'll be driving it for a while until the symptoms get worse while I save up for whatever I have to replace, be it the head, the whole engine, or the whole car. I've got no problems with the engine EXCEPT these weird symptoms at the moment; it hasn't affected anything I can notice in daily driving yet.

The reason I say complete car replacement might be wiser than engine replacement is that if this is in fact a catastrophic engine failure, this car already has rust at the inside door surfaces even though the outside's clear, it's in very very desperate need of a complete repainting to deal with sun damage, it's got air conditioning troubles (SLOW freon leak plus control unit issues), it needs a new rear windshield at some point as the separating corners gradually get worse over the years, the upholstery, while intact, is just barely hanging on... this car has had a LOT put into it and is still very, very valuable as a source of good, already paid for parts for the next one, but I'm not sure how many of these thousands of dollars I ought to throw at a body with doors that are trying to fall off and in which half of the electronics are insane.

For the moment those 3 questions I posted are the ones I need answers to the worst at the moment. Thanks for any input on whether there's any chance my problem is something other than a cracked head. And, either way, is there any further diagnosing I can do and report back the results of.