MFI issue on 1969 911S

[lopena]

I recently noticed that the oil level in my '69S has been increasing....the level was an inch or two above the "MAX" mark on the dipstick. I suspected gasoline was diluting my oil so I immediately performed an oil change. The outcoming oil was thin and smelled a little like gasoline.

I then referred to Wayne's book "101 Projects for your 911" which mentioned that fuel dilution of the motor oil is usually caused by a fuel leak deep within the MFI pump. However, I had the MFI pump professionally rebuilt two years ago by an acknowledged specialist, so I'm a little sceptical that a leaking MFI pump is my problem.

Question: is there something else that might cause diluted oil...maybe running too rich?

As always, thanks for your help!

Alan
New Jersey

[edmayo]

Since you 'recently' noticed this we can assume it had been okay previously. Has anything been done recently that would have caused a change, since the pump doesn't change settings by it self.

[lopena]

Ed:

The oil level had been fine previously.

The car was laid up all winter...I noticed the high oil level when I checked all systems after waking it from its slumber last week.

BTW: the car runs very strongly...no driving issues whatsoever.

One other observation...due to the cool weather here (60 degrees), I can't get the oil very hot (temp gauge shows about 170)...in fact, the oil lines to the front cooler are still cool to the touch even after a ten-mile drive. So, if the thermostat to the front cooler stays closed, could that cause a high oil level in the tank? Maybe the oil in the cooler and lines drained back into the tank and is stuck there until the oil gets past 180 degrees?

[edmayo]

That's a very good possibility ! So don't panic yet

[boba]

I would defer to Ed on all things MFI. I would question the thermostat allowing oil to flow back into the tank. That would mean that it was stuck partly open and then you would have oil flowing to the cooler when running and your lines to the cooler would be warm.

[lopena]

I would defer to Ed on all things MFI. I would question the thermostat allowing oil to flow back into the tank. That would mean that it was stuck partly open and then you would have oil flowing to the cooler when running and your lines to the cooler would be warm.

My theory is that the oil may have flowed back from the cooler into the oil tank slowly (drip by drip) during the winter months while the car was dormant. And since I haven't yet reached a high engine temperature, the oil cooler and lines are currently empty.

Again, just a theory...

[RSTarga]

Fuel from the MFI only gets in to the oil while running. Now that you changed the oil, check the oil for contamination after every run.
How many quarts of oil did you put in? How did you measure oil level if the engine hasn't reached the temperature required to open the thermostat?

[lopena]

Fuel from the MFI only gets in to the oil while running. Now that you changed the oil, check the oil for contamination after every run.
How many quarts of oil did you put in? How did you measure oil level if the engine hasn't reached the temperature required to open the thermostat?

David:

I put in 9 quarts, which got me to the middle of the dipstick range after a five mile drive. And, yes, I will do as you suggest...check the oil again after every run.

Hopefully with the warmer weather this week I'll be able to get that damn thermostat to open.

[edmayo]

Generally the oil drain back that occurs after long non-running periods is from the oil tank draining back into the case past the oil pump gears.

[silverc4s]

I would also defer to Ed on any early 911 issue, but I have learned from following Henry' s engine rebuilds at Supertec that he routinely isolates the MFI pump oil from the engine oil, and does not circulate engine oil thru the pump. Not sure how or how often you would need to check the pump oil level, but this would totally eliminate oil contamination thru the pump.
You could try it temporarily as a test.
What say you, Ed??