Re: I'm freezing in my tractor hauler..WHY??

Posted by Jon Hagen on December 26, 2000 at 23:03:57 from (63.160.195.147):

In Reply to: I'm freezing in my tractor hauler..WHY?? posted by Truck on December 26, 2000 at 14:29:56:

Had the same problem with my 80 GMC, Yours must be atleast an 85 if it has the 4.3 but the heater is the same untill the body style changed after 87.
This is what it took to make my non ac heater work in my 80.
1 after changing 195 degree thermostats several times and still couldn't get the guage to show more than 1/4 guage, I was informed by other GMC owners that this is normal, just how they (GMC)calibrated the guage.It gives the false impression that the engine is running cold.

2 the defroster vents have no screens in them so all the junk that gets thrown on the dash falls down the defrost duct and into the heater box and blocks the hot cool door slightly open which kills its ability to put out hot air.(Mine had 2 wood pencils 2 plastic pens,2 popsickle sticks and 1 chicken bone in it). If you remove the air outlet duct on the trans hump( 2 screws) you can dig out the junk.
3 after cleaning the air box you should check the adjustment of the hot cool cable, when correctly adjusted the lever should spring back slightly when you push the lever all the way to hot.If it does not spring back the door may not be completly closed. After doing this I had a good heater, replacing the 195 stat with a 205 made it a great heater.
On a non AC truck the water flows through the heater core any time the engine is running . It has a direct path from the intake manafold, through the heater core and returns to the suction side of the radiator. Some models return the water from the heater core to the suction side of the water pump. You adjust the temp by ducting air through or around the always hot core.
The engine thermostat has nothing to do with controlling water flow through the heater,all it does is restrict water flow from engine to radiator to maintain normal engine temperature. The bypass hose has no effect on heater operation or engine temperature, it is only there to allow some coolant to flow from the the intake manafold to the inlet side of the water pump, this keeps the coolant circulating through the block and heads while the thermostat is closed to prevent hot spots and steam pockets from forming. If your truck is newer than an 87 or has AC my experience may not help.

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