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Gotta make a confession. I had forgotten but the tstat that was bad was a napa tstat and not a ford tstat. Anyway ran the truck for a good hour and all is well with the mishimoto tstat back in and my coolant level set right. It never gets above the max line when at temp. I gotta say I have never had a tstat go bad before and was really unsure of all that could happen. The thing that clicks with me is the fact that with the bad tstat in the coolant level would fill the bottle fairly quick and cause it to puke acting like combustion gasses would. Also the second was the metal heater hose wouldn't get hot. At least I've learned a few tings on this one.
If you read my post, I said a stuck closed t-stat that suddenly opens after the coolant in the block is super heated. This will create a sudden increase in system pressure. May not last long but the cap is doing its job when this sudden increase in pressure happens and the cap pukes.
I did read your post but did not read anything about pressure in it.