Thread: Fuel in oil during extended ground time

I own a 2008 CTLS, purchased last October. Since May I have had problems with fuel collecting in the oil tank during several days of parking. Seems the longer it's parked, the more it shows as a higher amount on the oil dip stick. After flight when checked again, the oil appears normal in quantity and viscosity. The airport is over 6000' MSL, so all flying is high altitudes. Any ideas?

This can be normal at times. Not everyone experiences this, but many do. This is one reason to make sure your oil temps are up to the proper temps. This helps burn off/evaporate any impurities in the oil. This can be moisture, too. You may want to do an oil analysis for your next oil change. Fly it first then change the oil and take a sample in mid stream as the oil drains.

thank you for your suggestion. I have not done an oil sample yet. There are 40hrs on the HOBBS, and it's hangered in New Mexico, so I doubt if it's moisture. All fuel samplings have been clean, using non-ethanol 91 octane auto fuel for all than about 5 hours, which was 100LL.

I would check your float level in your carbs and make sure the valve isnt sticking open. Ive heard from rotax they have had problems with high wing aircraft with faulty viton valves, where when the aircraft sits fuel over flows out of the carbs and up into the venturi then into the intake manifold and past the cylinders. Usually in these cases there problems with back firing during start up associated with it. Other then that with such a high compression engine I find it hard to see how a noticeable amount of fuel would make it past both compression rings when operating but I suppose its possible. Like Roger had said any fuel or moisture in the oil will burn out after the engine has reached 212 Degrees F.

thank you for your input. I will pass it on to the mechanic.

I did forget and Jeremy makes a good point. You may want to pull the carbs and look at the float level. The carbs have to be off because you have to hold the carb upside down to do this. If the float arm is not adjusted right and it allows the level to be too high. The float arm measurement is 10.5mm from the lip edge of the bowl up to the top of the float arm. This is what regulates the viton needle and controls fuel flow. If they were off quite a bit it wouldn't allow fuel to be shut off while parked. You might get a little leakage like Jeremy explained.
How many hours on the plane? Are the carbs being pneumatically balanced every inspection whether it is the 100 hr or annual? Don't get overly worried, do an oil analysis next oil change after you have landed and the engine is still warm. Do you smell fuel when around the plane? If the plane idles a little rough this will puke fuel. Carb balance issue.

I would check the fuel pump, also. I am not familiar with the sealing inside the pump, but it is one connection to the oil sump where there is fuel on the other side. There was also a fuel pump SB a year ago. I am not sure what of the problem with the pump, but it is worth a check to see if you were affected and if you complied.

The fuel pump should not be the issue here. If it were you would see other bigger problems.

Do you turn the fuel valve off when parked? I cant see how you could get any amount off fuel in the oil tank with the valve off

You should get in the habit of always turning off the fuel valve when your done. When I turn the key off it comes out and the fuel is turned off. If any fuel does leak to the oil it comes from downstream of the valve and there is no way to do anything about this.