Ok, so my heater recently went on the fritz. The fan still blows fine, but I'm just not getting any heat. The only time I get any heat at all is when I have it on max, and even then I only get a little. My husband thought perhaps the mono valve had gone bad, but upon inspection we realized my heater does not use a mono valve.

What could be the problem then? The heater core? Any advice would be much appreciated.

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1983 240D, 272K+ miles (odo broke)

How's the engine temp? If it's not running at 80-90*C then you likely need a new thermostat. Running cool will give you poor heating in the cabin.
If you really don't have a monovalve, you've got a heater valve that looks like the one below. Make sure when you turn the knobs inside that you're getting movement at the valve in the engine bay. It's on the firewall on the passenger side. The arm could be stuck or broken.

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Yes, that's the part I have. The arms work fine.

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1983 240D, 272K+ miles (odo broke)

Is your engine temp where it's supposed to be? You could also have a clog in the system not allowing very much coolant to get through the heater system. You might take the hoses off the valve and see if there is anything inside the valve causing blockage.

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Have you got enough coolant in the system? (I don't mean to be rude)

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I will drive my car around the block in a little bit to see where the temperature falls at.

Yes, there is enough coolant in the car. That has not changed anything regarding how well the heater works, alas.

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1983 240D, 272K+ miles (odo broke)

I took two laps around the neighborhood just to make sure the engine would be completely heated up. On the first lap it fluctuated between 65 and 75 degrees (my guesstimate). For most of the second lap the needle was exactly at 80.

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1983 240D, 272K+ miles (odo broke)

With the engine at operating temps, and running, Carefully grab the heater hoses to feel how hot they are. They should be pretty warm to the touch. If they are not, then you are not getting any coolant flow to the heater. Causes for that could be a blocked heater hose --did the previous owner block off the heater core for some reason?--or low coolant level. If the coolant level is low, there will be reduced or no flow to the heater.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

Yes, they are warm to the touch. There is some minor coolant leakage on the arms of the heater valve.

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1983 240D, 272K+ miles (odo broke)

Is there a way to check airflow thru the heater? Is the passage free of leaves and other stuff? Can you feel air moving as you increase the fan speed?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags

I can only feel the air if I put my hand literally right over the vent. And that's when I have it on max.

ETA: Those were the two middle vents I was testing. The two side vents, I can feel the air from just fine, they blow beautifully. But the cabin is just not getting hot the way it used to.

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1983 240D, 272K+ miles (odo broke)

That makes it sounds more like an air flow problem. The heater vents are can be twisted to open and close the vents, are you sure they are open all the way. Not trying to make you feel stupid or anything, just want to rule out the obvious. The hose in behind the vents could have come off the back of the vent as well. You'll have to pull the under dash panel to figure out if they've come off.

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Edited my post just as you were replying, lol. *points up*

And yes, you may need to point out obvious things to me, I am not the car nut in the family

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1983 240D, 272K+ miles (odo broke)

heat does not come out of the middle vents. you should close those vents when running the heater.

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They are closed, but the cabin still doesn't get warm.

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1983 240D, 272K+ miles (odo broke)