Heater Hose Question, e30 318is

[Slowered318]

Can someone please verify the correct hose for inlet and outlet on the heater core?

If the arrows are correct in the first diagram then the water pipe is under suction and should be connected to the lower pipe on the heater core (without the valve). I assume the top pipe (with the valve) is the inlet to the heater core and the bottom pipe outlet, real OEM seems to have them reversed in the second diagram.

Really confusing! LOL

[Slowered318]

Need some help guys.

Since I changed all the hoses and removed the bypass valve (from the recall) I've been experiencing a strange problem with my cabin heater. I have almost no heat at highway speeds but when I come to a stop/crawl I have plenty. Engine temp and coolant level seems to be normal, I bleed the coolant twice using the uphill method to remove any air, tried disconnecting the power to the heater core valve. Checked over the system a few times and still getting the same problem at prolonged speeds above 50.

I have a feeling I might have connected the heater core lines backwards but it doesn't make sense that would have any effect. The heater core is just a closed loop from the head to the water pipe or does it have some sort of check valve? I've pulled over a few times and both lines to the heater core are toasty warm. I don't want to replace the heater control valve or thermostat if possible, they both seem to be working.

[DesktopDave]

I'll have to take a look at mine - I wouldn't figure direction would matter.  I also wouldn't think you have a bubble, but you never know.  Did you try flushing the core while the heater and ignition are on?

You don't have the bypass valve installed, but that was a fix by BMW to prevent the heater core from bursting.

[colin86325]

Sounds like the symptoms of reversed hoses.

[Slowered318]

I'll have to take a look at mine - I wouldn't figure direction would matter.  I also wouldn't think you have a bubble, but you never know.  Did you try flushing the core while the heater and ignition are on?

You don't have the bypass valve installed, but that was a fix by BMW to prevent the heater core from bursting.

I don't understand why the flow direction through the heater core would have any effect either. From what i've be reading, swapping the hoses has solved the problem for some people. Maybe I should give it a try but first I wanted to compare with some other M42's, just don't have access to any.

I thought a lot about the bypass valve actually. I don't get why BMW came up with this as a solution because it doesn't reduce pressure in the event of overheating, it just moves it from one hose to another. I had a little talk with mr. heater core and replaced the 2 bar with a 1.4 bar radiator cap. I won't drive with shorts on and we agreed it's gonna be all good.

[Slowered318]

Switched the heater core hoses and problem is solved.