heater blows cold, OVERHEATING

[BuNcHeSs]

My car is overheating, but only when I accelerate. It willll drop down slightly when not accelerating until it reaches the danger zone and I will turn it off.

It started out only on the highway and it would only reach about 3/4s of the way then go back to normal after driving below 60 mph. Then I went a cruise and drove it pretty hard and it overheated.

I replaced the thermostat with one I know is working, and the radiator cap, and I burped the system. The coolant levels are fine.

The only other thing I noticed that is noteworthy is that when it started there is a hissing noise coming from the passenger side that would go away. The heater blows cold air in any position of the "blower selection" and I let it idle for 15 minutes and could rev it up to 3k rpms with it never leaving the middle of the of the heat gauge.

 

[92AWDHX40]

Heater core, a leak, a bad head gasket, check those out, rule something out and go from there you may find the problem that way.

 

[Sebba]

Sounds like a head gasket issue bro. Make sure the cooling system is bled properly, and make sure the heater core isn't blocked.

 

[PrimerPLus]

My car was doing the same thing. Replace the heater core. It is most likely full of dirt, and junk. It's really not too bad to do it. Taking the dash out of the car is the hardest part, but all you need is an extra pair of hands and its no biggie.

 

[901gtsi]

I agree with sebba and primer plus its probably a clogged heater core try to blow compressed air through it the opposite direction the coolant usually flows through the core or just replace it. Check all the easy stuff before jumping to a bad head gasket. Hope this helps.

 

[BuNcHeSs]

Thanks guys! I appreciate the support, im going to take it in and get a radiator flush tomorrow. Hopefully that will unclog anything restricting the coolant flow.

 

[1glaserfwd]

A clogged heater core won't cause an overheating issue!! Are both the upper and lower hoses getting warm? It could be a water pump or clogged radiator also!

 

[1995silvergst]

my heater blowing cold was air caught in it I have a funnel that I wedge into the coolant cap and run the car up to temp. Rev it once in a while also, the funnel allows the air to come out of the system without making a huge mess and also allows for the expansion of the coolant without overflowing on the driveway. I would say if both your radiator hoses are warm at normal temp than there is still air in the system or you have a bad head gasket allowing combustion gasses into the coolant. Just my .02

 

[DSM1G90]

I'd take the radiator out and give it a very healthy flushout due they love to get massively plugged up in the lower section. One doesn't know how much junk and gunk resides in the lower half of any radiator.

Way to test heater core is to remove both hoses an send water through one end of the core to see how water flows out the other end. Being made of brass, the ends of the core can be easily bent and this will cause poor coolant flow through the core.

Ya, I need to do the same with my car .. tear the dash out to do a core replacement. Getting tired of driving during the winter with just warm air blowing out the vents.

 

[JusMX141]

Apparently you missed the giant merged thread with the exact same title during searching.