I just go my heater blowing air and I quickly realized that I have a host of other CC problems waiting in line. I have heat at low rpms but when I get on the interstate I just have air; not hot or cold just air. I have read several threads on this and it seems as though they are leaning towards the monovalve rebuild kit. Is there anyway I can test and make sure of this??

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http://www.libertyagrifuels.com
1984 300D Turbo
1980 300SD Sold
1983 300TD Sold
Dagger 16 ft. Legend Canoe (for the weekends)
Marin Northside Trail Mtn. Bike

You can easily take the mono valve out of it's housing and inspect for condition.

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83 SD

84 CD

I think you can disconnect the wiring to the monovalve and it will go to its default position and you should have heat all the time. Someone else who knows better will chime in I'm sure.

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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

This is correct.

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1989 300E 144K

Heat and alot of it.

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'83 300D Turrrbo 295K miles

That's true if the monovalve is functioning properly. But when the diaprhragm in the valve is compromised, it still won't work at higher engine speeds. In that case,the problem is a mechanical one with the valve; it's not an electrical control issue.

If you follow the advice in post #2, you are almost guaranteed to find your problem.

I guess what you are saying by compromised is the diaphram is torn?

what would happen if the cartridge was removed?

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

Ok. I know this is an obvious q/a but the monovalve is the box w/ the wire going to the top side of it and 4 bolts holding it on right. Isn't it located on the right hand side of the firewall near the battery??

__________________
http://www.libertyagrifuels.com
1984 300D Turbo
1980 300SD Sold
1983 300TD Sold
Dagger 16 ft. Legend Canoe (for the weekends)
Marin Northside Trail Mtn. Bike

That's where it is on your 300D- not sure about other models.

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'83 300D Turrrbo 295K miles

Coolant would blow out of the monovalve for a few minutes. Then it would stop. Then the engine would melt.

just bypass the valve with copper pipe

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1981 300SD 512k OM603

It's possible that your aux water pump is frozen -- a common problem. It would allow only a small amount of hot water to flow through the heater core, resulting in the symptoms you describe.

A frozen aux pump can also fry the ACC electronics, BTW.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Why would that restrict flow only at high rpm?

This is true, if the top was not replaced and screwed down with the 4
little fasteners.
What I was asking is if the cartridge was removed, and the top replaced,
coolant would continue to flow. the same as if the wires were
disconnected?

Charlie

__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works