Fuel in Engine Oil
 

Hello Everyone,
While pre-flighting my 377C I was having a hard time determining the oil level while viewing the dipstick on the rear engine. I did notice it looked very thin. The oil is pretty fresh. It did look like it was overly full, so I decided to drain some off. It poured out like water. What would cause this? Thanks

Oil
 

Is it fuel or water in the oil? If it is water, check to see if the cap is on the oil fill neck. Beside condensation, that is the only place I would thing water can enter the oil sump.

Jerry

Thanks for the reply, no, it's definitely not water. Everything was in place and secure, aircraft was hangared out of the weather. There was a definite aroma of avgas emanating from the "bucket 'o oil" and the oil was not milky, just thinned out. I've heard two theories....1) fuel pump needs to be rebuilt, or 2) the mixture cutoff was bumped back open while exiting the aircraft. Head pressure from the tank then allowed fuel to run into engine (the aircraft sat static for 3 weeks). Didn't know if anyone else heard of these things happening?

Does your aircraft have an oil dilution system? That will put a gas in your oil and a leaky dilution valve could do it.

I wondered the same thing about an oil dilution system, if the airplane has one I've never located it (I've had it for about a year and a half). Where would it be located? Could it have had one and it have been partially removed? The reason I ask is because the aircraft was refurbished.

There's a rocker switch for the OIL DILUTION SYSTEM. On my C model it is just to the left of the beacon/nav switch. I never had the system but the panel is labeled for oil dilution. There is a little info in the POH but have never found anything else in the SM. Maybe one of the fuel schematics might call out the system.

Preheating is preferred for cold weather over oil dilution so many planes have had the system removed. At the oil pump there's an inlet for the fuel, tracing backwards there's a solenoid valve which is energized and allows fuel to flow to the oil system. The solenoid gets its fuel at the strainer for early Skymasters. There's not much more detail in the Cessna maintenance manual and I don't have my engine MM with me at the moment.

Another possibility is the engine driven fuel pump seal is leaking allowing fuel to enter the engine from there. I've seen that happen before.
When's the last time that the fuel pump was overhauled?
Was your fuel consumption higher than normal, this wont show up on the fuel flow gauge, but the tanks would've taken more gas to fill up.

Drain all of the oil and replenish, fly local for 1/2 to one hour and check your dipstick again for the smell and the viscosity.

Dave