Red light time for Damages heads
       Well, over the last year I have had the red light on three times with blown hoses.  So I have fixed leaky thermostat housing, leaky distribution unit, changed the clogged radiator.  This engine has 70+ k on it.  A rebuilt GoWesty 2.2l. put in in 4-17-2009,  I replaced all of the coolant hoses, also.  Long story short, I have had mistreated the coolant system while in South American and in storage down there.  Had it filled with water only, most of the time. 
      It has been a little over two years back in the states with the proper coolant back in it.  My mechanic said that my system is tight, no leaks or compression gasses detected. Had a pressure check, a leak down test, and a compression check, and I also checked the expansion tank for exhaust gases(negative).  The Passenger side head that blew a gasket from over heating from a blown hose is only getting 120 psi in both cylinders (#1, and #2).[ I had that head check for damage, mechanic in Calgary, Alberta, said that there was no damage that he could see.]   The drivers side , #3 is getting 150 psi, #4 is getting 170 psi.  It is currently running a little hot, meaning the first level rad fan comes on earlier than it used to.  I have noticed that I am having to bleed the radiator of air often.  I have changed the blue pressure cap.  It only suck water from the overflow tank just after I have bleed it.  When I take an hour trip or more the running temp seems to go from the middle of the red light to just past it.  Then I check the expansion tank reservoir and there is air in it to almost the first return hose inlet.  If I run the van at 3800 rpm to 4,000 rpm it fills up with air, more quickly than if I keep the rpms down to around 3000 to 3400 over time.  When the expansion tank is filled up with air the overflow cap won�t refill the that space from the top up tank.  When I was thinking that I was running hot( temp gauge reading just above the red light position) , after a 50 mile drive, I had my mechanic check the temperatures of the rad  Normal-187, thermostat housing-187, water pump 190, and both heads 190.  I had just bleed the system the day before so the expansion tank was full, no air gap.  My mechanic thinks I am over reacting.  
      For some reason it seems the system is just not keeping up with the heat.  So yesterday I changed out the Thermostat.  I checked out the old Thermostat and it opened, slowly and not very much at the boiling point.  I also checked out the new one and it opened quickly and seemed to have a larger opening.  I also noticed that the old thermostat Meryle?, was a bit taller than the new Wahler?  both German made.  I ran the engine and gauge showed mid level and didn�t seem to climb.  As I revved the engine to 2500 rpm for a minute or more, I noticed bubbles filling the expansion tank, hm.  I think I might have had two problems, the thermostat being one of them.
      What is causing air to get into the coolant system?  Do I have a small crack somewhere in a head?  Or am I missing another possibility?
Frustrated, 
Gary Peebles
Seal Beach, Ca. 
and Paco(our Westy)