You say up to operating temp - what is that? My SD stays around 82C fully warmed.

If it's not that warm, try a new t-stat.

If it is, check or replace monovalve again (unplug to get flow) and check aux pump again. Otherwise, you might have a clogged heater core.

The ACC turns on the compressor in all modes except econ. Sounds like your A/C works better than your heater!

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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

It was like 45-50 degrees F when I left work this morning. I started the car and let it idle for about 3-4 minutes. I then did some around town driving for the next 10-15 minutes or so. I had heat but it wasn't really hot like it should be. When I got home the temp gauge was still below the normal operating temp. (80)

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Firstly, the aforementioned posts are correct..........the a/c is engaged in all modes but economy.

Second, the 617 does not put out much heat until the gauge gets over 60°C. and even then, the temperature is not all that hot.

Third, if you drove it around town.....at low speeds.......it does take awhile to warm up. A properly working auxiliary pump might assist in getting heat through the core faster. IIRC, you've verified this already, correct?

Fourthly, remember that the temperature inside the cabin is 50°F. before any heat is produced. Accordingly, the system will restrict the heat from the monovalve because the temperature in the cabin is approaching the setpoint (70°F.). Move the dial all the way to the stop to evaluate the capability for heat........independent of the dial setting.

And finally.........do we really need another thread on this.........you've already got one going IIRC? I might just merge this with the old one.

Your third point= I thought it strange that after 20+ minutes of around town driving that my car was still not warm. yes I tested the aux pump. (I stated this earlier in the thread)

Your Fourth point= I stated earlier in this post that I moved the thumwheel all the way to the stop. It should throw heat no matter what the temp inside or out.

Your Final point=There is no old thread. There WAS some redundant info so I took your advice and deleted it. I feel this is a valid thread because I am having strange, unresolved issues.

I don't know if I am just in a bad mood or not but I am getting a little pissy. If this thread is bothering anyone else feel free to delete it or lock it. Or I will do it myself.

My apologies ahead of time, I am on the rag.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

You seem to have all bases covered. I also seem to remember that you flushed the heater core........but........it was not fully clear??? Maybe you need to use the citric acid in the system for a hundred miles or so.

If the old thread is deleted, then it's fine to leave this one alone. But, it's always best to start a problem and continue it to the end on the same thread.........even if many months elapse during the diagnosis and repair.

When I flushed it didn't look bad at all. BUT the water just smelled really, really stagnant. I will give it more time and see what happens. That is what I don't understand, I seem to have tested just about everything and my heat is still weak. I just ordered a new thermostat to be on the safe side. I will see what happens when I install that. If there is any breakthrough I will post back here.

Thanks everyone.

__________________
'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R

Stagnant water could be telling you that the internal surfaces of the fins are rusted. If so, they won't transfer heat from the coolant. I had this occur with my tankless coil on the house furnace. After 20 years, the rust buildup on the copper fins prevents heat transfer. Finally had to replace the coil. Problem solved.

In your case, you've ruled out everything else. It's time for a good citric acid treatment. I'd leave it in there for at least 100 miles and drive the hell out of it, in an attempt to clear out the rust.