I bought my 1993 300D 2.5 last spring and the heater was great. The AC has been great all summer. But with this first cool snap yesterday, I noticed I had no heat. None, nada. Fan blows, lower vents work, just no heat. On the way to work this morning, I unplugged the heater (mono) valve and still get nothing (even on defrost).

I'm stumped. Where should I look for a problem?

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer

Are the heater hoses hot after driving? If the inlet to the heater core is hot and the out let is cold, could be a plugged heatercore.

How is the coolant level? Low coolant level can be enough to keep the car fom overheating, but not enough to make it through the heating circuit.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Does it have an aux water pump? Maybe that has either clogged up or stopped working. You can also pull the valve body out of the monovalve to see if the screen is plugged up.

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"I have no convictions ... I blow with the wind, and the prevailing wind happens to be from Vichy"

Current
Monika '74 450 SL
BrownHilda '79 280SL
FoxyCleopatra '99 Chevy Suburban
Scarlett 2014 Jeep Cherokee
Krystal 2004 Volvo S60
Gone
'74 Jeep CJ5
'97 Jeep ZJ Laredo
Rudolf ‘86 300SDL
Bruno '81 300SD
Fritzi '84 BMW
'92 Subaru
'96 Impala SS
'71 Buick GS conv
'67 GTO conv
'63 Corvair conv
'57 Nomad

Thanks for the suggestions. The expansion tank is a little low - I'd actually thought of low coolant, but expected that the tank would have to be empty to get no heat - I'll fill it and see.

I'll try to locate the heater core and check the hoses. This car is a bit more cramped in the engine bay than my '84.

It does have an aux pump, but I should get some heat on the highway without it and don't get anything.

Thanks again.

Any more suggestions?

__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer

Solution found!

Normally monovalves fail open - in which case there is too much heat. In my case, the valve was stuck partially closed due to crud (maybe from the rubber seal) being jammed in the orofice. This allowed only the tiniest amount of heat. After taking apart the monovalve and cleaning it, I have perfect heat again!

__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer