I just posted in this thread but I thought I should start a new one from me as well: http://www.explorerforum.com/forums/showthread.php?p=2635364#post2635364 I am having a problem with my 2000 SOHC with 120k. From a cold start the thermostat won't open until I get full hot on the gauge and the warning light comes on. When it does open after a few seconds the gauge falls back to normal and the heater starts blowing hot air. I also have the bubbles in the overflow tank when the engine is running and they continue for a minute or so once I shut it off. It does look like it's boiling from where the rad overflow hose enters the tank. When I get home from a drive I find the lid for the overflow tank will have popped open from the air pressure and coolant has slopped out of the tank. My gut is head gasket but I'm hopeful that a cracked thermostat housing maybe letting all this air in. There is no check engine light and the engine seems fine except for a low idle speed when in Drive (~500 rpm). I guess a compression check is my next option unless anyone has any other ideas? Has anyone tried bars leak - type products for head gaskets? Thanks!