PeachParts Mercedes-Benz Forum - View Single Post - Need to run something by you re: oil leak vs consumption

Ten13 · #14 08-16-2021, 07:56 AM

Hey All - a long-overdue update to my oil leak/consumption issue in the 81 300TD. Recall the excessive loss of oil over short interstate (about 150 miles = 1 qt oil) distances. Two MBZ specialist shops each said "rear main seal", so I did a more in-depth tracing of where the oil was coming from. It seemed to be (mostly) originating around the turbo assembly, and running down and eventually dripping from just to the right of the bell housing / torque converter vent area. While the rear main seal may be a contributing factor, it was not 100% of the time that a puddle would accumulate under the car when parked, or dripping was evident while idling. Oil residue under the car was mostly on the right side of the driveshaft, as well - more evidence that this was not main seal-related.

Faced with an engine overhaul, I decided to just drive the piss out of the car. I drove it to the eastern shore of maryland for mother's day weekend - 8+ hours of interstate each way. I'd stop and top up the oil every 150 or so miles, and restocked my supply when stopping for fuel. One gas station only had 5w-50 in non-synthetic. When I added that to my 150mi top-off, the problem simply stopped. I made it the rest of the way to maryland and then all the way back without adding oil (it was down about 1/2 quart, which seems like normal consumption) after about 700 miles. The car has been back & forth from Asheville to Atlanta with frequency - the same trip that revealed this problem in the first place, and no appreciable consumption or loss. It only leaves a few dime-size drips in the garage (as it probably has since new) these days.

Fuel economy is ~26-28 for all-highway driving, and it makes great power and less smoke.

Did running 5w-50 oil create higher pressure that freed up a check-valve in the oil system? Was it a stuck or occluded line that was causing excess oil to leak from the turbo housing, which accumulated more readily on highway trips? Not sure. The oil has since been changed with 15-w40, and everything continues to run like a top, if not better than ever. Oil pressure is about 1.0-1.5bar at hot idle, and immediately rises to 3.0bar with some throttle, under load or not.

I guess the lesson here is that the assessment of the two shops was based on a quick look, not an in-depth assessment. The car has been driving another 6,800 miles since the problem started, and has never run better during my ownership. These cars really do need lots of exercise!