First, oil consumption. I was looking through my Mercedes Benz Service Manual, Chassis and Body, Series 116.120 (300SD), Volume 1, and ran across this on the Technical data page 00-020/16: Engine oil consumption - 262 miles per US qt. We leak close to that!

Vacuum: How do would one know if it is a failing vacuum pump or a failing vacuum pump valve (from the pump to the brake booster)? Before I order a rebuild kit for the pump, is there a way to test if the valve is bad?

I ordered a complete set of offical Service Manuals quite a few years ago that are proving to be valuable, especially if they are read. However, they haven't revealed the above answer.

Jim W.

i do leak oil but ive only had to add maybe a quart in the last 3k miles to keep the line in between the notches on the dipstick

A failing pump will show low vacuum on a gauge and will have difficulty maintaining that vacuum when the brakes are applied.

The check valve prevents vacuum from being lost to the pump when the engine shuts down.

Use you mity vac and plug into the main line that comes from the vac pump and goes to the break booster. Plug any other lines that come from the main line, if there are any. Then start the car, and read what the mity vac says. If it reads at or above 20" Hg everything is fine. If not then you have a leaky booster or a malfunctioning vac pump. To find out which it is. Leave everything plug in the way it is and unbolt the main vac line from the break booster. Then plug the end of the line, I usually lick my thumb and put it over the opening. Then read the mity vac again. If the vac jumps up to the proper amount the booster is leaking, if it stays the same, sub par vac, then the vac pump is bad.

Hope this helps.

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Thank you. Things are pointing to the vacuum pump. With the line from the pump to the brake booster disconnected at the booster and no other lines open I have a reading of about 3.5 in. of vacuum, which is obviously very low.

Jim W.