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

charlie hill charliehill at embarqmail.com
Sat Aug 29 17:31:01 PDT 2015


The fan is working fine.  It even operates at two speeds.
Most of the time it doesn't run at all.  Occasionally it comes
on at low speed. The only time in 250,000 miles that I've heard
the fan run on high speed was recently while the thermostat
was sticking and that was what was wrong.  I just didn't get it
full of coolant when I put the new on in.  I filled it, ran it, checked
it, filled it again and it appeared to be full but only because the
thermostat was still closed.  When the thermostat finally opened
it allowed the coolant to run out of the reservoir and into the
system.  These trucks don't work like most of us are used to.
The radiator doesn't have a cap.  What we used to call the
overflow tank is now pressurized and has a pressure cap. (even though
the tank is clear plastic).  The hose from the overflow tank goes
directly into the water pump housing right behind the thermostat
so when the t-stat is shut the radiator is more or less out of the look
as far as refilling from the overflow.  That is what (I think) happened.
I drove it all over town tonight at low speed and idling with the AC on
and the temp stayed exactly where it is supposed to be.  Unfortunately
I didn't get the flange completely clean on the t-stat housing so I'm going
to have to pull it back apart and dump out 15 bucks worth of antifreeze
to fix a slight weeping on the flange.  That's ok,  I'll buy new hoses, 
flush the
system and fill it with fresh coolant.  250,000 miles, it's due for some 
fresh coolant
but what is in the system is clean and clear.  It's been a fine truck.

Thanks

Charlie

-----Original Message----- 
From: tmehrkam at sbcglobal.net
Sent: Saturday, August 29, 2015 4:56 PM
To: Antique tractor email discussion group
Subject: Re: [AT] HELP I'm stumped. truck problems, overheating

Does it have a Tstat fan?  Maybe it has failed.

      From: Darrell Ratliff <dbigdog at columbus.rr.com>
To: Antique tractor email discussion group <at at lists.antique-tractor.com>
Sent: Saturday, August 29, 2015 2:33 PM
Subject: Re: [AT] HELP I'm stumped. truck problems, overheating

Check the fan clutch.


From: charlie hill
Sent: Saturday, August 29, 2015 3:25 PM
To: Antique tractor email discussion group
Subject: [AT] HELP I'm stumped. truck problems, overheating

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

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