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No heat on highway, but lots at idle
Alright guys, I'm having a bit of an issue with the Benz that I'm noticing now that the weather is getting colder. At idle I get loads of cabin heat, however when I'm on the highway, I get barely anything.
Coolant level is up, and the thermostat is only a few months old. Anyone have an idea on what could be the issue? Car in question is the '85 300SD W126.
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'85 Mercedes 300SD W126 '99.5 Jetta TDI |
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Quote:
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'85 Mercedes 300SD W126 '99.5 Jetta TDI |
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take out the 4 screws in the top of the valve, remove core, replace with new core.
on your car, it's below the windshield inside the fake firewall about the center of the car.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
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I understand a torn diaphragm will result in heat all the time.
Sounds opposite from a malfunctioning recirculating pump tho. Any leaks in the system letting outside air in? Such as a pod flap that stays open.
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83 SD 84 CD |
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That would reflect a deficiency in understanding. No heat at high RPM is the classic symptom of a torn diaphragm. There are plenty of reports on this forum that support that concept.
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So what would cause heat all the time? That is another issue I have. Thanks
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Mad_Matt's Current Stable: Oil Burners: 09 Jetta TDI The highway queen @ 105k 83 300D. Sold Gassers: 16 A4 sport line 10 Passat 83 Recaro Trans AM WS6 Bone Stock Survivor 11 Harley Ultra |
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I thought a bad t-stat would cause coolant to constantly pass through the radiator. At idle, no air moving over the radiator, so he would get heat. At road speed, it would be over-cooling the engine... right?
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'85 300TD "Puff The Magic Wagon" - Rolling Resto '19 Mazda CX-9 Signature - Wife's sled '21 Morgan 3-Wheeler P101 Edition '95 E300d - SOLD '84 300TD "Brown Betty" - Miss this one '81 240D "China Baby" - Farm grocery getter |
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Depends on how it failed, but the symptoms as described are classic symptoms of a torn monovalve diaphragm.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
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heat all the time would be a stuck open diaphragm in the monovalve or it could be a defective CCU pushbutton unit. that symptom is classic for a siezed aux pump that has burned up the CCU board.
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread "as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do! My drivers: 1987 190D 2.5Turbo 1987 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
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A poor electrical connection at the monovalve would be a common cause.
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Sorry, can't be the first issue, ask tango.
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83 SD 84 CD |
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Quote:
Quote:
Thanks for the info guys. I'll order up that valve here later this week along with a new water pump since mine is leaking a tiny bit from the shaft seal.
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'85 Mercedes 300SD W126 '99.5 Jetta TDI |
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Answer
Quote:
* Blown CCU fuse. * Bad mono valve. * Bad ground to the mono valve. * Failed push button unit. .
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ASE Master Mechanic asemastermechanic@juno.com Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 1984 190D 2003 Volvo V70 2002 Honda Civic https://www.boldegoist.com/ |
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Agree
Quote:
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