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Dave Hutcheson 05-05-2003 03:28 PM

Pesky under dash oil leak
'85 300D 233K miles.

Hi folks.

Oil leaking down on carpet by lower drivers side heat vent - on center consule. Pulled under dash pannel and, yow! under-
layment saturated in black oil. Cleaned everything up and let the car idle for approx. half and hour. Oil pressure line tight and dry. Oil appears to have been leaking below key switch but nothing coming out during my inspection. Vacuum fittings on key switch like new - not bloated or disconnected.

Door locks work, trans shifts fine and engine shuts off like it should.

Threads indicate that it's time to replace/rebuild shut-off valve which is fine but I'm stymied as to why I couldn't find any source for what appears to be a substantial leak. I've owned the car for two years.

Help, please!


JimSmith 05-05-2003 03:43 PM


Try reaching around and feeling the connection to the back of the starting key/door lock assembly. There are two vacuum lines that are supposed to go to the back of the assembly, and the chances are it is leaking out of there. It is a sign of a bad vacuum diaphragm in the shut off mechanism on the fuel injection pump. I have had the same experience you had until the rubber connectors at the key assembly got gooey and slipped off. Good Luck, Jim

R Leo 05-06-2003 09:38 PM

Bourdon Tube Leaking
1 Attachment(s)
If there's no apparent leak at the fittings for the oil pressure gauge, yet you still have an oil leak, the most likely source is inside the gauge at the bourdon tube.

Nothing else in the dash can leak enough oil to make that kind of mess. Plus, There's plenty of things under there that would allow that oil to run across to the ignition switch side of the dash.

The bourdon tube isn't replaceable so you'll probably have to replace the entire left-side of the cluster (fuel, temp and oil are all on assy); but, they're easy to change out and relatively easy to find a boneyard.

A PO of Marlene had blocked off the gauge because of an oil leak. When I pulled the cluster apart to replace the gauge it was apparent that the source of the leak was a breach in the gauges' bourdon tube.

I have no idea when her leak occurred but it was still a mess under there when I got her.

BTW-I saved the old gauge mechanisim; someday I'll may try to find the leak and silver solder the hole so that I have an extra mechanisim in inventory for my Benz fleet...

matchsticks 06-05-2003 12:06 PM

oil in the dash
Hey there.
I've been right where you are my friend, and after much trial, error, conferring and head scratching, it came down to the oil pressure guage. Bottom line- replace the cluster. Much more experienced guys than myself were telling me I was nuts, but that was the solution. Best Of Luck

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