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Old 10-16-2007, 10:51 AM
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Join Date: Jul 2007
Location: georgia
Posts: 20
heater mono valve

good morning guys i just replaced the mono valve for my heater it is located on the left of the firewall. the replacement came with only one what i call a wavy washer. the old one had three washers i reassembled itthe way it came outwith all three washers. the good news is my heater works fine now. but the unit is leaking. does anybody know if the three washer assembly is the correct way to go or should it be just the washer that came with the replacement valve. it appears to me the previous owner might have been trying to make it work without replacing the valve by using extra washers. any help
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Old 10-16-2007, 10:59 AM
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Join Date: Mar 2003
Location: Convent Station, NJ
Posts: 755
Here are close-up pics of the assembly:

Credit to Holimont (Thom) for providing the link in a previous post.

'85 380 SL (sold)
'85 Carrera Flatnose
'71 280 SL Signal Red/Cognac
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Old 10-16-2007, 11:06 AM
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Join Date: Jul 2007
Location: georgia
Posts: 20

thanks for the pics. that is exactly how i replaced the parts. does yours make a little noise when you turn the heater on. mine makes a noticeable noise when the valve opens for the heater. i will have to look further for the leak maybe the short hose cant stand the pressure from the heater working. who knows off to another adventure finding the leak
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Old 10-16-2007, 12:22 PM
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Join Date: Feb 2003
Location: roslyn, LI,NY
Posts: 445
mono valve

What model sl and year? Misleading, can be a whole other type monovalve! Abe G
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Old 10-16-2007, 01:00 PM
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Join Date: Jul 2007
Location: georgia
Posts: 20

1989 560 sl. very low mileage 38000
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Old 10-16-2007, 01:50 PM
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Location: Arlington, VA
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The ones I've seen only had one of those wavy metal washers, but I don't know if all of them are the same or not.
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Old 10-16-2007, 05:34 PM
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Join Date: Mar 2006
Location: Upstate NY
Posts: 212
I believe that the monovalve is designed to operate with one wave washer. Apparently someone was trying to fix an internal leak of the seal. It's best to replace the internal parts. I don't think the monovalve should make noise. There is a slight click when it is on or off, but not continuous. Maybe you hear the hotwater pump that is connected to it. That little pump runs when the heat is on and the monovalve is open. Use a real long screwdriver as a listening device. Hold the tip on each part of the monovalve (when noisy), put your ear on end of handle. You will get a good audible sound when you are "on" it.
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