Oil leaking from my ignition switch? w115 300d - PeachParts Mercedes-Benz Forum

bgk202 · #1 02-04-2010, 09:34 PM

There is a very slow oil leak from the ignition switch area. It leaks from under the dash onto the floor.

I initially thought it was the line that goes to the oil pressure gauge, but that seems oil free. There are 2 or 3 vac lines going to the ignition switch (the lines or the switch itself are my prime suspects. Has anyone dealt w this problem?

thanks

Mike D · #2 02-05-2010, 05:54 AM

Vacuum shut down diaphragm on the rear of your injection pump is leaking. Replace it quickly before you get oil in all your remote vacuum diaphragms. Clean the oil from the line using a Mity-vac. Dip the line going into the rear of the injection pump into a container of de-natured alcohol and pull the solution through the lines using the vacuum container used for bleeding brakes.

meltedpanda · #3 02-05-2010, 07:53 PM

Mike hit is on the head, what year car?

79greaser · #4 09-12-2011, 10:16 AM

I have this problem as well. 79'300td. I have done a lot of reading and everyone seems to have slightly different advice as to where to start. I noticed some oil on the bottom loop of the vacuum lines attached to the ignition switch. Also the car won't shut off, the key has been incredibly hard to turn as of lately (only intermittently) and I have intermittent loss of brakes, usually at a stop. Please tell me these are all of the same problem stemming from a bad shutdown diaphragm. anything else i want to check? also, am i pulling the alcohol through the lines from where they attach to the switch?

Mike D · #5 09-12-2011, 12:56 PM

Also check your vacuum pump, the one in front of where the injection pump mounts. This is a known weakness of the 300's.

The vacuum pump is not causing the oil leak but it could cause the brake problem.

79greaser · #6 09-12-2011, 07:33 PM

thanks for the quick reply,
I checked the vacuum pump via the diesel giant method. I took off the 19m main vac line off of the brake booster and attached Mityvac. it reads 18hg. Seems a little low. Enough to cause a problem? Do I need to rebuild?

79greaser · #7 09-12-2011, 07:35 PM

Also,
I attached the mityvac directly to the shutoff valve with the car running gave it a few pumps, the line filled immediately with oil and the car died. With the car off i did the same and it does not hold pressure.

bgk202 · #8 09-13-2011, 11:57 PM

Until you replace the vac shutoff valve, just disconnect it and plug both ends (from the shuttoff valve so it does't keep oozing out oil, and the other side of the line to maintain vacuum). Then, use the emergency shuttoff lever on the IP to turn off the car until you can replace the shutoff valve.

As a precautionary measure - When you replace the shutoff valve, before you start up the car for the first time be prepared to plug the air intake to stop the engine (in case you install the vac shutoff valve wrong and end up with a runaway engine). I haven't replaced one of these on a TD, but on my w115 300d it is quite easy to install these wrong. To get it to line up right I ended up having to maintain suction on the valve with a mityvac until I bolted it in place.

79greaser · #9 09-17-2011, 04:34 PM

Thanks for the tip. I replaced the shut off. Had pressure on the valve while installing, put it all back together and I had a runaway on start up. Could have been scary without all the advice. Killed it via cd case over the intake. Worked great. Did it a second time without vacuum applied and I got it. Not sure what happened the 1st time. Car still does not shut off, but some of the squealing has quieted and the car just sounds much better. I see some cracks in the t connections. I did just do an oil change and may have leaned on them a bit too hard or something. Chasing down the many leaks.....

bgk202 · #10 09-18-2011, 12:18 AM

Hopefully now if you attach the mityvac directly to the shutoff valve with the car running it will shut off (without sucking in oil). If so, you just need to fix the vac leaks. First, test the ignition switch vac circuit by temporarily plugging all the aux vac lines (every small vac line except the line to the ignition switch and the line from the ignition switch to the shutoff valve), then see if the car turns off properly.

If the car then shuts off ok, then the leak is in your aux vac lines (lines to the hvac components and vac powered locks). Untill you find the leaks you could disconnect the vac powered locking system temporarily (if it is completely non-functional). I'd also suggest replacing any worn out, leaky vac check valves.

79greaser · #11 09-24-2011, 09:40 AM

So,
I did the test again on the new shutoff and no oil came through and the car shut off fine. I'm going to attempt to plug the rest of the lines and see what happens leaving the 1 to and from the ignition in tact. Not sure if this is related, but now I am having a strange clicking noise in the engine compartment that continues well after the car shuts off. Sounds like it is near the alternator. Bad Relay? Bad alternator? I just replaced the alternator a year ago. Could this be related to a vacuum leak? Thanks for all the help so far.

bgk202 · #12 09-25-2011, 08:20 PM

after you turn the car off, disconnect the battery. If the clicking sound stops when the power is cut, the problem is electrical (maybe a relay).