Jumper K Balls
Jumper K Balls PowerDork
12/6/17 11:48 a.m.

The BMW E28 has a climate control system that utilizes a mono valve. This is a normally open solenoid operated valve. It is NLA and the repair kits that are still available are utter garbage. When the valve fails you get heat at idle but as soon as the RPM passes 1200 the heater core goes cold.

That bugger there has been nothing but trouble since I have owned the car. 6 repair kits have been installed and all 6 failed within an hour. Some of the diaphragms tear, some loosen from the center of the shaft. My hypothesis is that they are for a different vehicle but are "close enough" that they should work.  I think they over extend in the valve body or something. I have actuated them on the work bench, everything seems good, but I barely make it 5 miles before the heater core goes cold again. 

That thing ^

Berk that thing.

at $32 a pop I was done. 


So this is where the bodging begins. I warn you, this is not pretty. It is however pretty GRM . wink

Amazon or eBay provided a 12V high temp rated 1/2" solenoid valve for around a tenner. A trip to the plumbing section gave me a 1/2" 90 and two 3/4" king nipples about $4. These valves are normally closed  though.  Rifling through the toolbox turned up a standard automotive relay with an 87a terminal. so 12v, a ground and the connector from the old valve to trigger it. The 87a terminal is the opposite output of the 87 so I have flipped the magic pixies. 

The result? I have heat for the first time ever in this car. However it is kind of the opposite problem than before in that the heat is weak at idle. There is a lot of internal restriction in this type of valve and it takes some pressure to open it. Were I to do it again I would use a 3/4" valve.

How long will it last? I worry that energizing that solenoid all the time will reduce its lifespan. I understand that the BMW valve was energized anytime the heat was off so it was running all summer, but I somehow doubt this $10 piece of gear is as ..... robust.


Yes I realize there are other valves at the junkyard that could be made to work.  Frankly the pick n pull type yards around here are overpriced and are only open when I am at work. It would be an ordeal to go look.


bugeye1031 New Reader
12/14/17 6:53 a.m.

We put over 220,000 miles on my wife's e28 many years ago.  I think I replaced that blasted valve four times.  I remember getting hypothermia one time when we got stuck in traffic for hours.  


Great fix - better than the original valve!  Good job!

gunner Reader
12/14/17 10:01 p.m.

I had heard that the cheap valve made by uro was trash and failed constantly. So I spent the 100 bucks and bought the bmw one through fcp euro(which has lifetime replacement warranty). had it in there for two winters, this will be the third and it operates as it should.

12/22/17 8:37 p.m.

when you havent owned an e28 in 6 years and you find yourself reading how to fix the climate control...

Trackmouse UltraDork
12/27/17 2:11 p.m.

Why has no one made a good electrical heater system that you can just wire up in a car?

Ransom PowerDork
12/27/17 3:00 p.m.

In reply to Trackmouse :

Because you've got tons of excess heat you're already working to get rid of from the engine, and taking a 1000-Watt hair dryer as a bare minimum (and it should probably be a multiple of that) amount of heat to put into the cabin, that's about 83 Amps at 12V. Which is more than the total output of the alternator on a lot of cars where you might wish for such a system.

They make cigarette-lighter powered defroster units, but my impression is that they work about as well as having a dehydrated squirrel hyperventilating on your package tray. (A well-hydrated squirrel would only increase fogging, of course) I expect they do nothing to actually raise the interior temperature significantly.

It takes a lot of energy to warm a car cabin, which is why electric cars bias toward things like heated seats for all passengers and heated steering wheels, since they're not already turning the majority of their fuel into waste heat.

Our Preferred Partners