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Old 11-29-2001, 07:56 PM
Mr. BILL's Avatar
Ghoulardi Rules!
Join Date: Aug 2000
Location: Austin, TX
Posts: 576
No Heat Question

My '90 300SE has no heat at all coming out of the vents. The blower works, A/C is fine, but no heat either while driving or parked.

I've done a search and it sounds like a mono valve. I don't know where it is located on a 126 and what the procedure is.

Help please.


91 300E 120K
90 300SE 275K (sold)
92 BMW 525iM 120K
90 BMW 525iA 175K
85 300D 175K (sold)
84 300SD 245K (sold)
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Old 11-29-2001, 08:37 PM
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Join Date: Jan 2001
Location: Tucson, Arizona
Posts: 758
Read the article to determine your problem

Greetings Bill,

Read the article I've emailed to you to isolate your problem. Sometimes it's just a matter of a frozen monovalve, or very hesitant in cold weather. In some cases the next time you start up you car, everything is fine again, (monovalve could be the culprit)

"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan
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Old 11-30-2001, 02:34 AM
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Join Date: Nov 2001
Location: Dallas, TX
Posts: 29
Don't forget to check your coolant level. I just had a similar problem and it was the coolant level. Check it with the engine hot and the heater on max. Also, the system must be bled well, or the fluid won't circulate through the heater core. If it seems like the coolant level is fine and you've bled the system, but still only get cold air, try this. Open the reservoir cap on the hot engine (be careful...) and leave it open with the car running. Then put the heater on max. Finally, rev the engine a couple of times. You should begin to feel heat come out of the vents. If all that works, to get all the air bubbles out of the system, you can open the bleed screw and replace the cap. Let the engine run with the bleed screw out till no more little bubbles come out. You shouldn't have any heater gurgling sound after that. Finally, top off the reservoir and you are done. I found the source of my problem to be a cracked gasket around the radiator cap, so i replaced the cap to avoid having to do all this in the future.

1990 300E

Don Drake

1990 300E 125k Miles
1994 S420 100k Miles
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