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#1
02-24-2008, 05:18 PM
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bubbling noise from the heater core
Hello there!
I hear a bubbling noise which appears to come from the heater core. Sounds like there is air in the system. Never heard it before. It happens at about 2-3000 rpm. The car is heating normally, I checked the coolant level and it appears normal, no leaks. Could this be the monovalve stuck open? Thanks Vlad 87 300 TDT 415,000 km
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Vlad B Toronto Ontario 1987 300 TDT 415,000 km on B20 since 2005; on Mobil1 since 2004 
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#3
02-25-2008, 11:25 AM
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mine does this as well, here is what I believe and tell me if i am wrong. I think this is caused by a monovalve that is only partially opening. When the car sits and runs at low RPM there isnt enough pressure to fully fill the heater core. When you do rev it up however the pressure elevates ant causes it to fill fully, hence the burbling sound. I haven't tried replacing the monovalve yet but i believe that is the source of my problems.
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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground. 1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers. 1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.
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#4
02-25-2008, 01:19 PM
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I get this on a 240D that does not have the monovalve. It is usually transient - it comes, gurgles for a while, then goes away for a while and comes back. Based on my experience I doubt it is associated with the monovalve. More likely an artifact of the actual geometry of the plumbing of the heating circuit that makes complete venting of the system difficult. Jim
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Own: 1986 Euro 190E 2.3-16 (291,000 miles), 1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000, 1988 300E 5-speed 252,000 miles, 1983 240D 4-speed, purchased w/136,000, now with 222,000 miles. 2009 ML320CDI Bluetec, 89,000 miles Owned: 1971 220D (250,000 miles plus, sold to father-in-law), 1975 240D (245,000 miles - died of body rot), 1991 350SD (176,560 miles, weakest Benz I have owned), 1999 C230 Sport (45,400 miles), 1982 240D (321,000 miles, put to sleep)
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#5
02-25-2008, 01:32 PM
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The heater core should not be "filled" by the monovalve opening, it should already be full. When the monovalve opens, it merely allows flow through the already full heater core.
Sounds like you have some air in the system. Not being familiar with the 240D, I don't know how common this is or how best to vent it. I do know that this gurgling took a while to stop after replacing the coolant in my 124, but eventually the small amount of air tends to get absorbed and carried out in the coolant (if just a little). A properly pressurized system will help.
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 Gone to the dark side - Jeff
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