You guys helped me with my brother's 3.8 Bonneville last month. It was his crank sensor just like you said. Now his heater blows cold. Engine temp is at 190*, but no heat. I'm guessing it is that vacuum operated valve in the heater line? You can hear his doors moving when he switches modes, and air blows from the dash, or floor or defrost. But just cold. So, is it that heater valve? Thanks in advance.
heater jeff, make sure the radiator is full. a radiator that is low more than a quart will effect the heater, yet could still run at 190 degrees. if its low add a 50/50 mix of anti-freeze and water. there also should bec a bleed valve on top of the thermostat housing. as the engine is running open the valve with a screwdriver. when you have a steady stream of coolant coming out it means you have bled out all the air. close the valve and fill the radiator and coolant tank. hope this helps.
Thanks John. Full of coolant, but I'll see about the bleed valve. What about the heater valve (isn't it called a bypass valve?)?
heater jeff, the next thing i would do is change the thermostat. a thermostat that is stuck wide open will cause a no heat condition. what year car is it? i dont think it has a heat control valve. heres another thing to check, with the engine completely warmed up locate the 2 hoses going to the heater core. both the heater hoses should be hot when you touch them. if one or both hoses are cold you could have a clogged heater core. a bad thermostat will also cause the hose/s to feel cold.
thermostat Jeff - Thermostat is easy to check on the car: start the car cold, top radiator hose will be cold to the touch. After a minute, feel the hose again. As the engine warms up, the thermostat will open and the hose will "suddenly" get hot when the coolant starts to flow through the radiator. Keep checking the hose, it should start to be hot after ~ 5 minutes. If after 10 minutes the hose did not get suddenly hot but gradually warmed up, the thermostat is stuck open. This will cause the car to run cold. Does it have a temp gage? - Bill
You didn't say what year it was....but 95-98 should be all the same. There should be a blend door actuator (little black box about 3x3x1) with three wires going to it, somewhere on top of heater case under dash. Most likely behind glove box. That little box has a tiny motor in it that goes bad and your Hot/ Cold blend door won't move without it. Most all GM cars use it now...... replaced ALOT of them in Lesabre's and S-10 trucks........ I think they are the exact same part Chev-Pont-Buick. Mike
Thanks all. We have replaced the thermostat 2x. It has a 190* in it now and runs OK. Temp is in the Normal zone. Isn't there a control valve that allows or blocks water passage to the heater core? It would be odd for a 7 or 8 year old car to have a blocked heater core, especially because we know the original owner and he kept the car serviced. Thanks.
heater Jeff - Many GM cars run hot water through the heater all the time: no control valve. They adjust the temp by using flapper doors to change the air flow. - Bill
Re: heater mmmm... interesting. We'll have to feel the heater hoses and see if they are warm or cold. We know the doors are moving because we not only hear them move, but the air is diverted to whatever location we select. We'll also look for a control valve too. Thanks.
Re: Re: heater Betcha it's the door actuator :Brow: GM Part #16141822 List $44.73 They are the first thing to go...... Mike
Re: Re: Re: heater Hey Mike, what does the actuator do? Does it divert the air to different outlets? The air shifts from floor to vent to defrost when we move the selector. If the door actuator does that, would it still change the location the air comes from? Or does it do something else? If it is that, how much of a pain is it to replace? Where is it located? Thanks.
Re: Re: Re: Re: heater There are seperate actuators for the heater/defrost modes and one for the temperature blend door. The temp motor just flips the door between the a/c side (cold) and the heater core side (hot). They are usually located on the top of the heater plenum right behind the glove box in that area. I'll attach a picture of one from an S-10 ...... they are very similar. Mike
AHHHH! So, even though we can divert the air from one location to another, the temperature door could be stuck in the AC mode, not allowing warm air to enter the car!? OK! We'll check it pronto!
Exactly! :TU: I've replaced a bunch of them........ the rear screw is a little tough to get out sometimes........ :rant: But at least there only two screws usually on them anyways.......... goodluck, and let me know what ya find! Mike
