I am picking up my "new" 83 300D in the morning. It has 220.000
miles, it seems to have been well kept. No rust, and for a Detroit
car I thought that was a good indication. I am excited...however
don’t want her to become a money pit!
Anyway ~ it has a few problems. The pass. window (I have read several
threads on that and think I know what the deal is there). The tach
doesnt work, the locks dont work in unison and it shifts hard from 2nd
to 3rd at fast speeds. And the heat is hot only in idle. From the
research i’ve done I’d guess all of that is related to a (shift
modulator?) or a vacuum leak.
Does that sound right? (wouldn’t need a rebuilt trans would it?
How hard is it to find and fix a leak? Is that a mechanic thing? I
read about replacing the monovalve to fix the heater issue. Will that
fix the tach and lock system too? Forgive my ignorance as I am new to
diesel altogther. I just want to roll using straight veggie oil, that
is my goal. Any advice I’d really appreciate.
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First get the basics right then go to the Bio - because it will give you
some initial problems so keep that project on hold until these get fixed.
The tach is just cosmetic eye wash - nice but so what.
The heat is probably the monovalve - it can be rebuilt with a kit, but
before you attack it be sure the motor is operating at 80 degrees C. If
not, install a new engine thermostat.
Vacuum powers the door locks, engine shut down and transmission shift
harshness and the climate control ducts. A vacuum leak will affect
these. Transmission will shift harder with less vacuum, the heater
problem could be related and the door locks typically are vacuum related
- because the leak is often in the locks.
You should know that to start these diesels in bitter cold weather a
good battery is needed and you should preglow it two or three times
before cranking to heat up the chambers. Key ON wait about 10 seconds
after the glow plug light goes out, turn OFF, then ON wait 10 sec. and
finally crank it.
On Jan 26, 2:33 am, "-->> T.G. Lambach <<--" <"T.G. Lambach at
The tach problem is most likely the tachometer amplifier. . Google
and you;ll find a recent thread here on that. It's the barrel shaped
diagnostic test connector widget, about the size of a can of tomato
paste, located in the engine compartment by the driver side fender.
It screws off by hand and has about $1 worth of electronics in it that
turns the signal from the flywheel sensor into a voltage for the tach.
Takes 1 min to replace, but try removing/replacing it, as there is a
chance it's just a contact issue. They go for about $60. Other
possibilities are the tach or the sensor.
I'd suggest you get this car checked out by a mechanic before you buy
it. You say you don't want a money pit, but with a car of this age
and mileage, it is going to require more ongoing maintenance, with
anything possible. I'd be especially concerned about the tranny,
which is already misbehaving. I would not assume it's just a minor
Also, to run on straight veg oil, you do realize you are going to need
a conversion kit, right? That consists of a seperate new fuel tank,
and piping, controls, etc that allow the car to start up/shut down
running regular diesel, then switch over to veg oil when the car is
warmed up. Otherwise, in Detroit, the veg oil will solidify in the
lines, injector system, etc and the car ain;t going anywhere till you
get a nice warm day.
Have somebody who KNWS THIS MODEL OF CAR look at it. This
cannot be understated.
Usually a switch. They just pry up; disassemble, clean put back together
and it'll probably work. You can short the wires together bypassing
the switch to verify this. Could be a fuse too (but not if it's just one
window as they're in diagonal pairs on a fuse) or a bad motor (unlikely).
Vacuum leak. Probably a door look actuator. Harsh shift are ok,
the trany will wear less quickly if it shift harshly - less
wear on the clutches.
Thermostat or clogged rad.
No. Get a vacuum tester. "Mity Vac" or equiv.
No heat is monovsalve or heat stuck on but not sometimes off sometimes on.
Tach is easy:
Need Mercedes parts? http://parts.mbz.org
Richard Sexton | Mercedes stuff: http://mbz.org
Agreed on all matters... the heat problem can be two fold... if engine temp
not holding 80 degree on highway, then it is thermostat. Otherwise, it is
the climate control amplifier/monovalve... monster unit and costly... which
is most likely the culprit.
That could be vacuum but could be not. My '79 TD has mis-functioning
door locks that are due to the springs that allow internal override
(e.g. you can unlock the door from the inside if the car has been
locked) being broken. I haven't been able to locate this spring
individually, and when I'm at the dealer I'm not sure what part it's
attached to, so I may just have a hand at fabricating the spring myself
(there are pictures in the manual, so what the hell?).
I also have a vacuum leak that's as of yet undiscovered, but the car
works well enough and I don't keep much in it of value so I just don't
lock it. ;)
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