[AT] HELP I'm stumped. truck problems, overheating

[Steve W.]

charlie hill wrote:
> Ok guys, my 06 GMC 5.3 liter engine started
> overheating when first started up.  It would get up
> to about 220 or 230 degrees.  I could turn the heater
> on and get NO hot air flow.  Then all of a sudden
> it would start to cool and the heater would blow hot air.
> OK easy, bad thermostat.
> 
> I go and get a new t-stat and put it in.  Same problem except
> worse.  Now it gets up close to 250 before it starts to cool down.
> I took the old thermostat in the house and put it in a pot of water on
> the stove with a cooking thermometer in it.  It opens and closes as it
> should.
> 
> Anyone got an idea what is going on?  For those not familiar with
> the 5.3 GM engines the t-stat is not in the intake like GM motors of
> old. It's in the front of the water pump housing so it should not be
> prone to having an airlock at the thermostat.   I see no sign
> of bubbling in the coolant.  I'm not loosing an appreciable amount of
> coolant and there is no sign of coolant it the water or out the exhaust.
> I did however have to add some coolant a few weeks ago which is unusual
> and I have smelled an odor that smells like a coolant leak.  It's the same
> odor you smell in the cab when a heater core is leaking.  But I haven't 
> found
> any sign of a leak anywhere.
> 
> Right now I'm sitting at home with both of my vehicles not running.  I need
> answers quick.
> 
> Thanks
> 
> Charlie 
> 
> _______________________________________________
> AT mailing list
> http://www.antique-tractor.com/mailman/listinfo/at
> 

Classic symptom of an air pocket.
You could borrow a pressure tester and make sure you don't have an 
unknown leak, but I would bet there is air in the block. I routinely 
vacuum fill systems now because many use a pressure tank system and are 
a PIA to get all the air out...

-- 
Steve W.