arster

cannot get any heat with mono-valve connected with 12 volts


when mono-valve is unplugged and the rotary dial at cold


MB only heats at idle, when RPMs advance cool air from vents only

ncdave

sounds as if we have a similar problem. 91 350 SDL

oldsinner111

have you checked usual stuff like thermostat,hoses.Mono valves are a replacement item,some places have kits for them.Is the heat control unit working.

ncdave

I did take it to the local M-B repair center and had the mono-valve replaced. I can get some heat with the mono unplugged and over 2k rpm at times. The "plumbing " is right. I am supposed to take and leave at another M-B place.

arster

Thank You,
I am still looking

brbhan

If replacing Mono valve did not help for heat at idle, indicates mono valve was not at fault. Problem points heavily to auxiliary water pump - located by mono valve. you might notice bluish stuff on it indicative of slow, coolant leak. Its purpose is mainly to provide heat at low idle (foot off the pedal).


Note: Ensure no air in cooling system; eliminated by keeping reservoir cap off and bringing engine to warm up. Also ensure coolant level is OK. Initially, check often. I have experienced low heat if level is even slightly low. Best! Basil

Plutoe

What's the VIN!!

brbhan

This specific model was only available in US in 1986 and 1987 (w/minor upgrades over '86). Mine is an '87 as well, manufactured August, 1987.
Frankly, I do not see how my VIN is relevant to your issue.
Cheers, Basil