Im having a problem with my heater in my 75 mav. I let the car warm up to operating temperature, and when i turn the heat on, it blows out warm air for about 15 seconds, then rapidly cools down to cool air (not even lukewarm). But if i shut the heat and blower/fan off, and turn it back on about 20minutes later, it blows out lukewarm air, then rapidly cooling down again. Any ideas on Whats wrong?
If u need to use the heater, I wud replace the core - soon - before it leaks in the car and cuz rust issues. If it's not leaking already. A least expensive is to disconnect the hoses and by-pass the heater.
X2 Reverse flush it and do it gently at first! I made mine leak by connecting it directly to a water hose! I'd start out by just holding the end of your heater hose to the end of the water hose. That way you won't build up too much pressure in the heater core. Apparently they are pretty fragile! Edit: Also if you have a heater control valve (AC car), it may be stuck shut. The valves always leak a little fluid through so if you have the fan off, the core would eventually get hot.
All great suggestions, but also make sure that your heater control valve (if equipped) is operating properly.
True, but if the engine does warm up and the heater works for several seconds, I don't think it's the thermostat. I know when mine was bad (stuck open), the engine never warmed up and the heat was steady but barely warm.
If the car isn't moving then the engine would heat up. Once you get rolling and get air flow through the radiator it will cool down faster than what it would if it only had the air from the fan pulling air through the radiator.
It does not have A/C. And the thermostat isn't stuck open, the coolant circulates as it is supposed to. I had flushed the radiator, but I didn't (should have) Flush out the heater core. The coolant level is normal also. So i think I'll flush the radiator out and continue from there. Thanks for the advice!
Flush the heater core...Its plugged. Battery acid actually workes well to clean em out but...A 40 yr old core may spring a leak doing this. You can buy a cooling system flush agent or...Pour some CLR in the core and let it soak for 20 minutes to loosen the sediment, then flush it out with water (Garden hose is fine). Be certain you direct the discharge hose away from yourself or the car (Underneath the car is good) You may have to do this more than once. Just flush it till the water runs clear and is free flowing.
let motor warm up , turn fan on and feel the heater hoses, if one is cooler than other one you have plugged heater core or regulator valve which is in hose coming from water pump, if same feel readiator hoses to see if car if warming up to proper temp, mite have bad thermostat
