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Old 09-26-2003, 01:45 AM
Registered User
Join Date: Sep 2003
Location: S.F. Bayarea
Posts: 196
Smile Hi, first time 300SD owner


You guys convinced me to get sooty with a turbo diesel. So I just got a 83 300SD, 185K miles. Good shape with a few door dings and bumper scrapings. The paint is in excellent condition, no fade. This is my first MBZ toy. Wish me luck! Wife's C280 is not to fool around with.

I'm currently catching up with the basic maintenance. The fuel prefilter is black, the air filter is dirty, etc. I have a few questions:

1. The trans fluid level seems very high even with a cold engine. The trans dip stick have two horizontal line marks, and the fluid level is near the bottom "twist" of the dip stick. Are the two horizontal lines mark the max and min level?

2. AC blows cold through center vents, but side vents blows hot air. Time to rebuild monovalve?

3. Any pointer to get valve adjustment tools?

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Old 09-26-2003, 01:51 AM
unkl300d's Avatar
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Join Date: Jul 1999
Location: San Francisco, Ca
Posts: 2,404
1. yes, and It seems your trans fuid may be low. but you have to check it with engine hot and running but in PARK.

2. side vents are where the hot air comes from. If you experience both cold and hot at the same time, then something is loco.
As far as I know, the monovalve needs changing when you can NOT get hot air.

3. call Phil at partshop or fast lae. even if it is not on the catalog he can get you tools.

good luck!
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
1979 240D 140Kmiles (bought for parents) *SOLD.
1989 300SE 148 K miles *SOLD
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Old 09-26-2003, 03:48 AM
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Join Date: Sep 2003
Location: S.F. Bayarea
Posts: 196
I thought the monovalve should block the coolant flow if AC is on.
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Old 09-26-2003, 06:11 AM
vwbuge's Avatar
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Join Date: Sep 2001
Location: Johnstown, Pennsylvania
Posts: 2,116
Special tools are NOT absolutely necessary but they do help.
'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
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Old 09-26-2003, 03:14 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,834
Someone explained it to me but I don't understand it completely. When the monovalve seal ruptures, you get some heat at idle and low speed and almost no heat at speed. Coolant flows through a loop that bypasses the heter core.

It's easy to pull the monovalve in an SD. Pull it and check that the mesh screen is intact and clean and that the rubber seal is supple and intact.

Also check that the monovalve gets a solid ground through one wire with the AC on max cool. The other wire gets a constant +12V.

95 S420
91 300SE
87 300SDL
83 300SD
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Old 09-26-2003, 03:25 PM
rickg's Avatar
User friendly
Join Date: Mar 2002
Location: Utah!!
Posts: 4,494
Congrats on buying the best car in the world, IMHO
Center vents are for cold air only. If you're running the heat, close the center vents.
past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)
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Old 09-26-2003, 10:28 PM
H-townbenzoboy's Avatar
Now Y2K Compliant
Join Date: Jul 2003
Location: Houston, TX
Posts: 4,336
I just want to say, welcome to the 300SD club. You'll get great membership benefits such as...
1. Driving a "Big Body Benz"
2. Getting luxury
3. Getting economical mpg
4. If the car smokes, you can just floor it when someone tailgates.
5. It has the classic MB look, and has a little modernity in it still.
6. The strong, dependable W126 body and OM 617 engine, think of it as the ultimate 80's diesel Benz combo
7. Get a smooth ride
8. The car as a whole is just great!!

Good luck, and keep on klatterin'...
Board Member of MBCA|Houston

81 MB 300SD, 82 MB 300D Turbo (sold), 04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.
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Old 09-27-2003, 01:20 AM
Registered User
Join Date: Sep 2003
Location: S.F. Bayarea
Posts: 196
I'm thrilled to find such a heavy duty ride. I'm sure the drive train can handle more than double the specified power. Can we say "industrial strength"?

I find Pindelski's site extreamly helpful, and I happened to have the same model, 83 SD....

There is a filter (like a VW bug fuel filter), which was shown in his transmission tuning pages near the switch over valve. Does it prevent fuel contaimination to the vaccum system? What is the key word to search for more info? I need to put one in.

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