monovalve
Senior Member
Joined: Dec 2006
Posts: 437
Likes: 168
All Cars Lost To Hurricane Isaac (W124 E420 revived - added 88 Allante 14 S550, 17 S63
Your statement "overheating" brings the following to mind;
1) if the engine is "overheating" then having a leaking (open) monovalve would allow some of the coolant to dissapate thru the cabin heater and thus should help lower the engine temp (at the expense of your comfort)
thus, the high engine temp would indicate issues in addtion to the monovalve. the vent heat does indicate monovalve issues
2) if the "overheating" is within the cabin (and heat from the vents as you stated), this could be a monovalve issue alone
1) if the engine is "overheating" then having a leaking (open) monovalve would allow some of the coolant to dissapate thru the cabin heater and thus should help lower the engine temp (at the expense of your comfort)
thus, the high engine temp would indicate issues in addtion to the monovalve. the vent heat does indicate monovalve issues
2) if the "overheating" is within the cabin (and heat from the vents as you stated), this could be a monovalve issue alone
Thread Starter
Junior Member
Joined: Aug 2010
Posts: 32
Likes: 0
300E
i agree there are more issues. head and head gasket just got done, oil leaks fixed, just ordered a reservoir cap, replaced the thermostat. the aux water pump and electric fan both work, but only when i jumper directly to them. the only things left that control these is what? relay, coolant temp sensor? please bear with me, new to diagnosing
Junior Member
Joined: Nov 2009
Posts: 54
Likes: 0
From: vancouver, b.c.
1990 300e24
the monovalve, when open controls cool/cold air to come inside the car, when its closed/unplugged/broken only heat will come through the vents at only 1 temperature...hot. If the engine is over heating it is helpful to turn the heat on full blast in the car, you'll be able to see the temp quickly drop but its not a fix.
Thread Starter
Junior Member
Joined: Aug 2010
Posts: 32
Likes: 0
300E
i believe i'm having both issues. i get hot air temp only coming from the defrost vents with no control over the temperature or cabin fan blower, and while driving the engine temperature will stay around 80 to 90. when i stop the car the coolant will begin to drip out the reservoir. strangely the hoses feel real hot but they won't feel hard from the pressure built up. soft and spongy.
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Junior Member
Joined: Nov 2009
Posts: 54
Likes: 0
From: vancouver, b.c.
1990 300e24
well there should definitely be no coolant dripping out haha. I don't think the two problems are related but the interior situation is the monovalve. Replace it and all will be well, if you cant find one at a wrecker online i think they are around 120 or something. Cant be much help with the engine over heating stuff though sorry.
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Newbie
Joined: Dec 2010
Posts: 4
Likes: 0
1974 350SE Euro/1988 420SEL
re: valve
I can't find one in my car, the hoses by my battery are connected to each other and this car is new to me so I would like to see where that valve should be on my 88.
