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heat works only at city speeds
so i took my car for a 240 mile trip yesterday and when im around town the heat works good but once i get on the hwy the heat blows cool, not super cold but not warm either and the temp gauge reads abt 80 so i was wondering if anyone had any idea what could be the issue... also my 2 middle vents on the dash wont blow any air out either, the vents open but no matter what i select on the selector panel the air only blows out of the defrost and the 2 side vents. any ideas would be greatly appreciated.
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1985 mercedes benz 300D turbo diesel 1998 VW GTI VR6 1996 VW GTI 2.0 1999 saab 9-3 turbo 1987 300sdl (sold) |
#2
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Do a search on monovalve cartridge.
Sixto 87 300D |
#3
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Lack of flow
The root of your problem is usually poor coolant flow through the heater core. This causes both problems- as the car goes faster there tends to be less heat, and because the air is not getting heated the climate control senses that condition and stays in heat mode to compensate which results in the center vents not opening.
Many times the monovalve simply needs to be replaced. There are a bunch of posts on this topic. In my case the heater core was not flowing well and it took a through flush of the cooling system to solve it once and for all. In addition to the symptoms you described I found that if I slowed down a bit on the highway and gunned it in third gear to get the engine up to about 4000 RPM it seemed to get the coolant flowing enough to start things working temporarily and I would get heat for five or ten minutes.
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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!) '95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs) Deuteronomy 22:4- "Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again." |
#4
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95% of the time poor heat on the highway is due to a bad monovalve diaphragm. Its an easy replacement and then you'll have heat back. Just do a search on it.
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-diesel is not just a fuel, its a way of life- '15 GLK250 Bluetec 118k - mine - (OC-123,800) '17 Metris(VITO!) - 37k - wifes (OC-41k) '09 Sprinter 3500 Winnebago View - 62k (OC - 67k) '13 ML350 Bluetec - 95k - dad's (OC-98k) '01 SL500 - 103k(km) - dad's (OC-110,000km) '16 E400 4matic Sedan - 148k - Brothers (OC-155k) |
#5
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Not disagreeing with the monovalve suggestions, but you should also make sure your cooling system is up to snuff. 80 C is just a bit on the low side for coolant temperature. You might consider changing your thermostat if/when you open the cooling system. Also make sure your pressure cap is good and the system is holding pressure when hot.
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1987 W201 190D |
#6
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A small tear in the monovalve diaphragm will still allow it to function at low speeds but at consistent highway speeds coolant is forced thru the tear from the higher pressures producing symptoms like yours. Could be something else but it only takes 2 minutes to check your monovalve.
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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 |
#7
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Look, pull your monovalve insert out and take a look at it. As stated, 95% of the time that causes these exact symptoms, and we hear about this all the time.
Other answers are valid, just makes poor sense to start with the more complicated stuff, especially when it isn't that common. And as far as I know, 80 degrees C is fine for an engine temp. It isn't like these gauges can be trusted to be perfect to a single degree anyway.....
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Jimmy L. '05 Acura TL 6MT 2001 ML430 My Spare Gone: '95 E300 188K "Batmobile" Texas Unfriendly Black '85 300TD 235K "The Wagon" Texas Friendly White '80 240D 154K "China" Scar engine installed '81 300TD 240K "Smash" '80 240D 230K "The Squash" '81 240D 293K"Scar" Rear ended harder than Elton John |
#8
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Quote:
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1987 W201 190D |
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