1994 GMC Yukon Heating issues

CHICO03

MEMBER
1994 GMC YUKON
5.7L
V8
4WD
AUTOMATIC
150,000 MILES

I have no heat and I've replaced the thermostat heater core and water pump. Checked hoses for blockage or collapsing. Checked and replaced fitting. Checked hvac actuator. Still no heat. Replaced antifreeze. Truck will get to temp about 195 to 210 then drop down to about 150. Used a temp gun to check Temps on everything. Put cardboard in front of radiator. Covering half and nothing. At idle it will blow cool air but when put under load the air warms up. But not hot. At a loss please help.

3 Replies

HMAC300

MECHANIC
48,601 POSTS

It shold be a 195 degree t stat, check to see if both hoses get hot when engine warmed up. It may have an air lock in system so check radiator cap. Check for a vacuum leak at one of motors and see if vacuum is going to any of them.

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Friday, October 23rd, 2015 AT 6:36 AM

CHICO03

MEMBER
2 POSTS

Only the hose from the back of the intake gets hot not the one going to the water pump. I just replaced the t Stat and made sure it's a 195. I have a new r cap just haven't put it on.

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Friday, October 23rd, 2015 AT 6:41 AM

HMAC300

MECHANIC
48,601 POSTS

Your heater may be plugged then as both hoses should be hot. Check for blockage in hose to pump or maybe an air lock causing problem. Check radiator cap as it may not be building any pressure.

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Friday, October 23rd, 2015 AT 6:51 AM