77BlueL82

Went out shopping with the wife tonight. Car ran great….except no heat when I got above 60 MPH. When I slowed down there was heat. Could it be that one of my heater hoses is air bound? Someone please help before my wife deserts me.
BTW new top radiator hose and new heater hoses done in August.
:confused: :confused: :confused:

PB82CE

Thermostat working?? Temperature setting?? Heater core clogged??
Just a few of the "Obvious" items and my .02... :bb

Big Fish

If the engine is running at a reasonable temperature (over 170) you should have plenty of heat providing you don't have a vacuum control problem in one or more of the control dampers. I would look for a problem there first, or even a vacuum leak, possibly under the dash or anywhere in the vacuum system. Unlikely you are airbound.

77BlueL82

Thanks guys.

Engine is running at about 190 deg. Would the vacuum change that much from 50 mph to 65 mph to make a difference? I hear the dampers moving when I change from a/c to vent to heat to defroster.
:confused: :confused:

Big Fish

The vacuum could change enough. If the engine is staying 190 the vacuum is really the only other variable. It is a different damper used for temperature control than the one used for defrost/floor/ac. Try hooking up a vacuum gauge so you could take some readings while driving?

77BlueL82

Thanks. Time to check out the vacuum diagrams. :sad:

Big Fish

Just looked at my 75 heater control unit, the bypass damper for the heater core air flow is mechanical, not vacuum operated. Could be enough of a vacuum leak where you might be grabbing too much outside air from the intake damper located in the area of the windshield wiper transmission on the passenger side. Vacuum would hold that damper closed so you don't get outside air. If you are losing vacuum to that damper the temperature of the outside air could overcome what the heater core is capable of doing. Also in your year was there a vacuum operated valve on the heater hose? A loss in vacuum there could cause problems as well.


[Modified by Big Fish, 10:43 PM 12/16/2002]

john's '81 mouse

Quote: "Also in your year was there a vacuum operated valve on the heater hose? A loss in vacuum there could cause problems as well. "

You can go ahead and check out your vacuum operated heater control valve if you have one, but I doubt it's the problem, and certainly is not the problem even if no vacuum to the valve, since it's open to the heater core when no vacuum, and only closes when A/C is turned on and then vacuum is supplied to the line which is supposed to close the valve.

It may be possible that the old valve is cruddy, and is sticking, and is not opening fully when no vacuum is applied to the line. A new heater control valve can be purchased from GM or auto parts store for around or under $20.

BB wowbagger

No heat in a C3?Usually the question is " To much heat".. :lol: :lol: :cheers:

Twin_Turbo

It may be as simple as a low coolant level, the first signs are no heat inside the car, and when it gets worse the coolant temp will spike, so check your coolant level too