I spoke with my mechanic today and he said that the clips holding the piston to the connecting rod had broken off. This evidently caused large/deep gouges in the cylinder wall (from the piston hitting the wall, I guess). He said he had never seen this happen before. He does not think it is due to coolant leaking into the engine but can't really give me a good explanation of how this occurred.
The sequence of events went something like this:
1) Noticed slow coolant leak. The resevoir tank would drop down to the min position. No pools under the car, no clear indication that coolant was leaking into either the engine or transmission. Heating coil was not affected. Filled the resevoir tank and about 4 days later noticed the same thing.
2) Took car to mechanic #1. He performed a pressure check and replaced the thermostat/housing and sent me on my way.
3) 4-5 days later, the coolant light comes on and the resevoir is back down to "min". I take it back to mechanic #1 and he does a pressure test overnight and also does a compression test. He says that everything is ok and there might be an air bubble in the coolant system (which makes no sense to me). He tells me there is a chance that the gasket has a small leak but it will cost over 2K to replace it. I decide to take it to another shop to get a second opinion.
4) Next day, my wife is driving the car home and tells me that it is shaking. I check it out and it is idling very rough. I have an appointment to take it to another shop in a couple of days so I just let the car sit in my driveway until then.
5) I take it to the other shop. They tell me that the first thing they did was a compression test and there was no compression on cyl #5. OK, that explains why the car is shaking. They open up the engine and find that the cylinder has been gouged and the pins/clamps holding the piston to the connector rod have failed. Again, they say that they have never seen this and "it shouldn't happen."
6) Result is a new engine. Evidently the gouges are really deep and cannot be machined out. I am going to the shop on Friday and see exactly what they are talking about.
I don't think it was the timing belt as I am pretty careful about having the scheduled maintenance and I believe that it was done not that long aog. Anyway, the second mechanic checked that and didn't note any problem there.
Well, that's my whole sad story and I hope can learn something by it.
-Zag