overlooked cooling system part: heater valve (a.k.a. water valve)

[aurelius]

I've mentioned this here and there within a few threads and have been meaning to give it a home, so to speak.

Late summer, 2009, my mechanic calls me. Which is a rarity. I did not have a car at his shop at that time. He implored me to replace my heater valve, a part he had begun to see causing catastrophic cooling system failure on E46 models.

This part isn't seen in cooling system rehab kits, etc. Part number is 64118369805. It's a BMW-only part but, as of this writing, ECS Tuning has a very good price at $67.

If your HVAC is erratic, with hot air coming from some vents and cold from others, your heater valve is likely failing.

Bonus: it's a super easy DIY. See HERE. Do it on a cold motor and you'll lose negligible coolant.

[kayger12]

Good advice.

Adding this to my spring project list.

[telijah]

I do agree in it being an over looked part and is a likely cause of erratic heating scenarios, but I have not heard of it being a reason for the cooling system itself to actually fail catastrophically. But yeah, if you're having heat problems with the A/C unit, and it is not a low coolant or bad t-stat problem, this water valve is usually the next in line to check. I also think that is the reason why it is not found under the cooling system diagrams on realoem.com, but instead found under Heater and Air Conditioning.

Also, in very very rare cases, when you have the warm passenger air vents, which is almost always a low refrigerant problem, this water valve can also be the reason.

[aurelius]

For what it may be worth, I got on the ball with this when I had burning hot air coming from the footwell vents, even with the a/c on & all setting on full cold.

I'll clarify with my mechanic in terms of how exactly it causes cooling system issues but my guess is that the valve sticks in a way that builds up pressure and blows one of the hoses off.

Which is consistent with what happened last summer to a friend in his E39 in the middle of Manhattan on a Saturday night. Big steam and coolant show, traced to failed heater valve.

[telijah]

Ah, that does make sense I suppose.

[danewilson77]

Over filling is also overlooked.....which I think is the same thing.