87 300SDL my heater only blows warm air! What can be done to make it hotter?

The temp gauge runs at 80 degrees C with an outside temp of O degrees F.

Like I said all I get is just warm air I think it should at least blow hot.
It would be nice to set it on the EC & auto setting with the temp dial @ 22
and not worry about it, but it needs to blow on high just to get comfy.

Does the auxiliary water pump move the coolant to the mono valve?

Yes........unless its seized.........

Yes you aux pump moves the heated coolant through the monovalve. Have you taken the four screws off the top of monovalve and inspected diaphram and cylinder? It could be stuck - also is the temp sensor working and un-obstructed? A recent problem here involved a moth that had died and blocked the sensor.

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98 E300 DT
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97 S500
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86 300SDL
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The mono valve is maybe 3 years old, I do have a new one setting in a spare parts box.

The temp wheel does move freely and will switch to cold air when dialled down to the blue settings. I just think I should be getting better than warm air.

Is there a way to test the auxiliary water pump? If it wasn't functioning would that affect the amount of hot air blowing out of the vents?

It's not all that easy to determine if it's running, but, you could give it a try. It runs under all modes when heat is demanded. Without the pump, the coolant flow is mediocre until the engine is at highway speeds. However, at the ambients that you are currently suffering, I'd suggest that the flow at highway speed might also be inadequate for very high heat.

The best test is to pull it out of the vehicle and connect it to a battery. Then, you'll immediately know if works. But, you don't want to do it now.

I'm going to go out right now and put in the new valve.
I have a non-heated garage but I'll be out of the wind....ah it's warmed up some, it's up to 9F

Since you're goin' in............look for the removable section of forward firewall. A couple of screws takes it out and you'll be able to see the pump...........and, possibly determine if it's running when you put your fingers on it.

I don't know where you live but every fall my monovalves tend to stick closed from not being used for 10 months of the year. It may be just that simple. The aux pump is removed from one of my 126's - don't believe you would notice unless you were in a serious cold area and idling a lot.
Don't confuse the temp sensor with the temperature control wheel.

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15 VW Passat TDI
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98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

Watch the little screws - I usually ends up sacraficing one to the firewall. If the diaphram looks ok, just hit the valve with some 000 steel wool.

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15 VW Passat TDI
00 E420
98 E300 DT
97 E420 Donor Car - NEED PARTS? PM ME!
97 S500
97 E300D
86 Holden Jackaroo Turbo D
86 300SDL
(o\|/o)

Used a magnetic screw driver.