I'm about to install a new heater core because I have fogging windows in my 1990 240. There seems to be nothing leaking on the floor, and I don't have my recirc. on. I do know there is a problem with my heater control valve because it's either really hot, or cold...there is no "warm" air when you set the temp gauge in the middle.

Will replacing the Control Valve solve my problems? I'm probably wishfully thinking since I don't want to tackle the heater core issue.
Thanks.

For What Its Worth...

My 1980 240 has the same full on / full off function. Almost any morning I turn the heat on I get a puff of fog and it clears right up. Been doing that for as long as I can remember. No water leaks. Original radiator and heater core, too.

Watched a guy do the core replacement thing once. Not my idea of a fun weekend.

Chuck2

If it's any help or consolation, they're pretty much ALL "on or off" heater control valves. I wish they'd regulate as well as the one in my 740...
The very late model year ones (92-93) seem to work much better - I don't know if this is because of a design change or just that they're younger.

Good luck and I hope you have no leaking heater core.
Have a pressure test done on the cooling system with the heater valve fully open- that ought to confirm a leak.
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Rob Bareiss, New London, CT 86 244, 87 244, 88 744

The fogging probably means you have a small water leak at the heater. I have two 240's with the bad heater valve and neither of them have the fog problem although they both have the "all on or all off" feature. Your valve could be leaking though. I'd do the valve and then the heater core if it still fogged up. Ugly job.

Thanks for all of the advice. A local shop told me to try aluminum stop leak to the coolant...which may get me through the winter. I also applied Rain-X interior anit-fog, and it works really well. I'm hoping a dose of the stop-leak will work well enough as I don't have any leaking on the floors, and only the haze through the vents. I've done a lot of jobs on my 240, but dread taking apart the dash.

One other tip from a person who's taken his 240 dash apart for heater service, twice. If you have to go into the heater for _any_ reason, you may as well replace everything you can while you're inside, much as when you've got the front of the engine off. In your case, you're going to end up going in for the core, but be sure to do the fan motor, and think about getting one of the fancy modified ones with ball bearings if you plan on keeping the car for a while. There's almost no repair job I don't enjoy doing once just because I like getting a firsthand look at things, but the dashboard evisceration is just no fun at all the second time. Worse, it's so fiddly and involved that I was only able to cut about an hour off the job the second time around. A full day's work, and be sure to have a masseuse lined up for when you're finished.