No Heat

[gould10]

I have a 1998 4.3 with 166,000 miles. I will turn the heat on and have heat for about five minutes then it turns cold. Some times I will have all heat and others no heat. My radiater is full and i changed my thermostat. Next thing I will do is flush the radiater I guess. Any ideas before it gets to cold here in michigan. Thanks

[ronterry]

Not knowing that system in any detail, but my guess would be the gates that open in close in the heater/AC box.

Not sure if those are electric or vacuum, but it sounds to me that it could be a short or leak in the devices that control the opening and closing of those gates.

 

If it's vacuum, with a leak in the system it could cause the doors/gates to revert to there non vacuum state of being closed and no heat. Why it last 5 or so minute could come down to expansion and contraction of material at different temperatures.

 

I know with my Vette it uses an electric motor to control the hot/cold gate, and vacuum to divert and blower output. Hope this helps some, and I do realize these are two different beasts.

 

There might also be a deverter in your heater hoses also ?????

 

Ron

[citydriver]

The plenum doors are driven by electric motors...When it loses heat, check to see if the heater hoses are hot...if 1 is HOT and the other is COLD it could be AIR-LOCKED, an air pocket in the heater core....that would be the 1st thing I would check

[harlan]

Had same symptoms as you. Replaced/flushed all parts,etc.....Turned out it was a plugged up quick disconnet fitting on intake manifold.

 

$10.00, and I was able to get it out of the manifold without breakage.