Bizarre. What about block and oil temps? I would expect the block to be getting hotter than desired without proper circulation. Very strange. Do you live in the Twilight Zone or an alternate dimension?

Wow this is a fairly perplexing situation. I'm still leaning on there either being a blockage in the block or as you said some kind of crack in the water jacket that isn't letting water flow. But in that case you would still get an area of very hot water for a time, or at least I would think so.

One more idea to throw out there. Try flushing the system in different areas. What I mean instead of just forcing water through the thermostat housing down try maybe forcing it through the heater core, through the heater return line through the water pump. There has to be a reason your engine isn't getting to a proper temperature.

Jan

If you are getting 160 degree water to the radiator with a 190 thermostat, then I would suspect the thermostat is stuck full open. That would explain the slow warm up at least. Try a new one and see how it works.

Good Luck

Test the T-stat first on the kitchen stove.I had FOUR bad T-stats in a row.Three of them were Mr.Garbage ones and one was new from the dealer..

Is there any sort of coolant flush that would dissolve out corrosion, possibly freeing up any blockages? Maybe something acidic? It might be something a radiator shop could help you with.

I have a product in there now from Prestone and have a demo product to try next that is supposed to be awesome. Not big on Prestone stuff. I don't know the specifics on the new stuff, the service director for GM just spent 8 hours at school on it and came back pretty impressed.

As for the 'stats, yes, I have checked all three on the stove and all three open when they are supposed to. Something is busted inside I am certain of it. But now that I have a little heat, I'm just going to drive it until it breaks. Only downside to that is that it won't break down in a "good spot", I'll be miles from home or some such thing.

Leonard