Hello Pagodameisters,
My ’68 250SL (early version, euro) has started leaking oil past the oil filler cap on the fuel injection pump. The pump is an older model (R18z) which I understand has its own oil reservoir independent from the engine.
I’ve done some homework on this problem – there are a lot of words written on this forum about it – and I’ve learned that the usual cause is fuel leaking past the pump pistons and filling the oil reservoir. That makes sense… but I have reasons to think this isn’t what’s happening with my car.
Some background: The car had been undriven for about a year. I installed a new battery and fired her up and drove it for a few miles with no problems. The engine ran smoothly and there were no oil leaks while running. A few days later, I idled it in the driveway before taking my wife to a nearby restaurant. I noticed an oil spot in the driveway when pulling away. When I arrived at the restaurant, I looked under the car and saw an alarming amount of oil drizzling onto the pavement. I shut off the engine and checked the crankcase oil level to find it was on the halfway mark of the dipstick. After our dinner, we went back out to the car and the oil was no longer dripping. I started it up and got full oil pressure on the gauge. I watched the gauge as we drove home and made it back safely. Again, the engine ran smoothly, but oil was still drizzling out while it was running. I checked the oil level on the dipstick again and it was now approaching the low mark.
Later, I topped up the oil and inspected the car when running. That’s when I discovered the oil flowing past the red (Oel) filler cap on the injector pump. I took a syringe fitted with a thin plastic tube and drew out roughly a liter of oil from the pump. It smelled only slightly of gas. Assuming the pump originally held 200ml of oil, and that it was being filled with fuel, this fluid should have been about 80% gas, and reeking of it.
So I changed the crankcase oil and I refilled the pump with about 180ml of 10W30. The car started more easily than before and the engine ran smoothly. But after about 10 minutes, oil started flowing past the red filler cap again. Afterwards, I syringed another liter of oil out of the pump. It was dark and, as before, smelled only slightly of gas.
Since then, I’ve managed to find the pump’s dipstick. It took only 90ml to fill the pump back to the mark, so I may have somewhat overfilled earlier. But I don’t think that’s relevant to the underlying problem.
So my questions are:
1. How in the devil is the pump filling up with oil if it has an independent oil reservoir?
2. What are my next steps in diagnosing and resolving this problem?
I'd be grateful for any of your insights!!
Steve Smith
Atlanta
