Took a drive to PA and back last night and barely any heat. When I warmed the car up, I was up to 60C on the temp gauge, but dropped just a little once I got rolling. After driving a few hours, and being late, it was cold-like 10-15F. The temp gauge was at the first line, and blowing lukewarm. I was reading in another post that there is an electronically controlled valve, that the contacts might need to be cleaned. There is a hose coming out of the back of the motor, and it drops down below the windshield washer tank, and what appears to be a valve with 2 wires attached is right underneath. Then a hose runs off of that to the firewall. Am I correct with this possibly being the culprit? When warm, the car is never above 80C on the gauge. I never did the thermostat since I had the car.

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1990 300D 2.5
1991 F350 7.3 Dually IDI

1997 F350 gasser dump
1980 H-D 93 inch Shovel
2000 SE Roadglide

Found some pics online. Is the part I'm describing under the washer tank the pump for the hot water? And the valve I'm looking for-the mono valve- is that what limits the amount of water? Thanks

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1990 300D 2.5
1991 F350 7.3 Dually IDI

1997 F350 gasser dump
1980 H-D 93 inch Shovel
2000 SE Roadglide

Try cardboard in front of your radiator.

The valve your speak of is a called 'mono valve', it allows flow through the heater core (small radiator inside the car you get heat from). Stuck shut valve = no interior heat. Mono valve is over by the battery. It's on the output flow side of the interior heater coolant circuit.

Down below the washer tank is the aux coolant pump.. this is on the input side of the interior heater coolant flow it helps push coolant through heater core, and is useful at low engine speeds, putting around town. On the highway, you should have enough push from the main water pump on the front of the engine to more than enough flow through the heater core.

Suspect your interior coolant temp gauge and check the engine with an infrared temp gun. Point it at the head between injectors to get readings.

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Cheers!
Scott McPhee

1987 300D

Last year I put the cardboard up, but from reading other posts, I should have heat. On my old Ford diesel pickup the cardboard is a must. Going to check the mono valve. Thanks

__________________
1990 300D 2.5
1991 F350 7.3 Dually IDI

1997 F350 gasser dump
1980 H-D 93 inch Shovel
2000 SE Roadglide

If the engine is not getting to the proper temperature, that is your real problem. You should not need to block the radiator if the thermostat is working correctly.

If you are desperate for interior heat, yank the mono valve and put hose mender in its place to allow straight flow through.

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Cheers!
Scott McPhee

1987 300D

I have to agree with Craig, hot engine before hot interior. If the engine isn't getting up to temp, your thermostat is the first thing I'd check.

I drove mine last week, needed to go out of town and the only available car, it was 6F when I left the house and I was up to 85C on the gauge (while running the heat) within about 4miles of rural driving. On the freeway at 75mph, it maintained about 80F, with the heat on (wagons take more out of the heater also with their bigger cabins). Not normal to be below that, and cardboard is a crutch in anything less than arctic temperatures.

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Gone to the dark side

- Jeff

Going up steep grades it gets hot in a hurry, then cools off just as fast on the downside. Still doesn't get close to 80C. I checked the connections on the mono valve and everything looked fine. Do those valves last, or are do they fail often? Anywhoo, I'll start with the thermostat. thanks

__________________
1990 300D 2.5
1991 F350 7.3 Dually IDI

1997 F350 gasser dump
1980 H-D 93 inch Shovel
2000 SE Roadglide

They normally do, there is a cheap repair kit for it on this website.

But look at your thermostat first. Your car should heat up to 80*C and stay there, not fall down.

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-Typos courtesy of my mobile phone.

On many cars, a low coolant level will result in insuficient heat to the heater core. Have you checked the coolant level? Start with the simplist things first.

Don't worry about the heating system until you correct the engine temperature, then the heat will probably take care of itself.

Just for the record, if the monovalve fails, usually removing the electrical connections will give you full heat. But I agree with everyone else, sounds like a bad thermostat.

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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

the part about the heat climbing quickly concerns me. you said it never gets to 80 though... how high does it get?

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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!

Might be an indication that it doesn't even have a thermostat in it. I assume these have bypass thermostats like the 123's.

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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

In the summer it may get a hair above 80C on some long drag uphill, but always levels back off at 80C. When it's cold out, it gets to 60-70 maybe. But if it's 15-20F out, it will stay at 20-30C , at 70mph on the highway. I'm going to disconnect the mono valve and give it a run. If the heat comes up and stays there, I would assume it's a bad valve. But as far as not getting too hot in the summer, I would suspect a stuck open thermostat.

__________________
1990 300D 2.5
1991 F350 7.3 Dually IDI

1997 F350 gasser dump
1980 H-D 93 inch Shovel
2000 SE Roadglide