W115 1975 Mercedes 300d excessive oil consumption

[IM75300d]

Hello all, nice to meet you all. I’m pretty new to the group and recently picked up a 1975 Mercedes 300d.

It has been going through quite a bit of oil, about half a quart every 100 - 150 miles, and the oil seems pretty thin and smells like diesel. I had been reading in the threads and thought maybe the injector pump might need new oil, but it looks like the 300d injector pump shares oil with the engine. Again kinda lost at this point so any help would be much appreciated!!!

[Diesel911]

Originally Posted by IM75300d

Hello all, nice to meet you all. I’m pretty new to the group and recently picked up a 1975 Mercedes 300d.

It has been going through quite a bit of oil, about half a quart every 100 - 150 miles, and the oil seems pretty thin and smells like diesel. I had been reading in the threads and thought maybe the injector pump might need new oil, but it looks like the 300d injector pump shares oil with the engine. Again kinda lost at this point so any help would be much appreciated!!!

If the fuel injection pump is lubed by the engine there will be a plastic tubing from the engine block to the fuel injection pump. The below is going to be only about those pumps lubed by the engine oil.

There is a little O-ring inside of the fuel supply/lift pump that separates the oil side of the fuel injection pump from the fuel side.

That means fuel can get out of the lift pump and that drains into the crankcase of the engine mixing with the engine oil.

The other case I have read about is that the engine oil from the inside of the fuel injection pump gets sucked into the fuel supply/lift pump mixes with the diesel fuel and gets burned as if it was all fuel.

Or maybe in your case both are happening.

It sounds like you need your fuel supply/lift pump replaced or rebuilt.

However, be cautious as there is a fuel supply/lift pump valve kit that does not come with the small 5mm O-ring that you need.

The next caution is the flange on the fuel supply/lift pump is a think brittle casting and you need to be careful not to bend/brake it during removal and installation.

[Sugar Bear]

^^^Great advice...

Be careful, don't let this go as fuel in the oil thins it greatly and will cause fast wear of crankshaft bearings and the camshaft.

IIRC the 300 pump of that era was oiled from the black plastic tube and the 240 was an oil bath contained within the pump. The 240 had a plastic cap on the pump that read "OEL" where oil was added to the pump, the 300 didn't have this.

[vox_incognita]

Some help with part #'s .

A0000900210 -valves & springs kit :

https://www.pelicanparts.com/More_Info/0000900210.htm?pn=000-090-02-10-MBZ&srsltid=AfmBOoqwvbe-9X0Ir7jAN4Dcxgh-b-BXL69ZUjhZv7HXCir54AgsvgU1



A0000911280 - gasket, lift pump to IP

https://www.pelicanparts.com/More_Info2/0000911280.htm?bc=c&SVSVSI=

Bosch 2440210002 / MB A0109978648 / VOLVO 240270 / VOLVO 6885605 / Caterpillar 2Y 5809 - o-ring, plunger rod (the one described in the above posts.Bosch are green color,Viton). OOS with Pelican atm.