Heater blows cold air above 40mph...

[aw3som3dud3]

So here is the story, I recently did the M30B34 motor swap (car is so much fun now!) on my 84 318i everything was going great until I needed my heater... Now I have plumbed up my heater by running a hose from the outlet on the back of the head to the heater core and from the outlet it goes to the coolant distribution pipe. Heater works great!! as long as I stay below 40mph, when I speed up the heater turns into an artic wind storm machine. Coolant temp gauge never gets to normal operating temps (I have an electric fan hooked up to switched power but am working fixing that) so its not over heating, so no air trapped..


I have a thermostat im going to throw at it since im not sure when It was last done, it does have 340K on the motor..i do have a leak at the water pump, I have a gasket coming for that.


Would accidently swapping the inlet and outlet on the heater core cause this artic wind storm? its just weird if I stay below 40mph it will roast me out of the car, if i hop on the freeway it turns balls cold in there...


Im lost, HELP!! my hands are going to fall off from frost bite if I don't get this sorted.


Thanks, Tim

[ThatOneEuroE30]

I have my cooling system routed like this with a 75 degree thermostat all works great


It is possible that you could of done this i went through same issue of no heat in my car but at idle and it was from the hoses being flopped. Coolant will take the path of least resistance when flowing like anything else. You could also have an air bubble trapped.

[aw3som3dud3]

So is the inlet for the heater core the top or bottom pipe? I have it set up as the top is the inlet.
















That is how I have my hoses routed but im using the B34 upper radiator hose not the B35..totally get path of least resistance, but my temps are not rising when heater is blowing cold, it stays right around the line before the middle.

[ThatOneEuroE30]

Heater blows cold air above 40mph...

So is the inlet for the heater core the top or bottom pipe? I have it set up as the top is the inlet.
















That is how I have my hoses routed but im using the B34 upper radiator hose not the B35..totally get path of least resistance, but my temps are not rising when heater is blowing cold, it stays right around the line before the middle.

The heater core inlet is the bottom hose. So mine goes from back of the head cause i have a b34 to the bottom pipe on the fire wall. The top is the outlet. My temps didn’t rise either in fact i sat at 1/4 when cruising and half way at idle and after i fixed it my temps stayed the same but i got heat!

And fyi after flipped hoses to correct orientation. It was a BITCH to bleed was probably out there for 3 hours letting it rise up to 3/4 and then killing it and letting air out and repeated this probably 2 dozen times

[aw3som3dud3]

Awesome! thanks a million, my hands thank you more...

[ThatOneEuroE30]

Awesome! thanks a million, my hands thank you more...

Lol yea i didnt have heat either when it was 20 degrees out. Those were some cold ass drives