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Engine Lubrication Oil Overflow

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Hi Gentlemen,

As stated in subject, I got this overflow. It was yesterday when I wanted to fly for the first time after about two and a half months break. When I manually turned the propeller for the gurgle, oil overflew from the oil tank and spilled on the ground. I checked the oil tank and it was too full indeed.

Last time I did the oil change it was about four months ago. I remember I put the required amount of oil and flew the plane a couple of times without problem.

As I am almost sure oil doesn't multiply like bread, which even not any one can come along and start multiplying, some other fluids like cooling liquid or fuel might have entered oil circuit in some way.

I Checked cooling and it appeared clean and in the right quantity. So I am wondering if fuel could get there and increase oil quantity enough to bring it to overflow? For info, fuel lock was actioned, so if it works fine fuel shouldn’t have been able to get through.

I checked the floaters of the carburettor and one of the four displayed an overweight of 0.67 Grs compared to the other three. In all cases I plan to order new floaters tomorrow Monday (man they don’t come cheap).

Can the floaters be one of the possible causes for this overflow?

Can fuel pump leak too and let fuel go into engine and go into lubricating oil?

Any other reason you see or imagine that can be the cause of this overflow?

Many thanks in advance for stopping by and for your thoughts.

PS: it's a Rotax 912S

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56 minutes ago, CT2K said:

I put the required amount of oil and flew

I think you likely overfilled it. The amount required includes the amount you failed to drain.  Flying a couple of times without problem doesn't guarantee that you were not overfilled.

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This reply comes from my husband, who is a Certified Rotax Repairman:

When you changed the oil did you first rotate the prop to pump all of the oil out of the engine case?  Did you change the oil filter?  If not, this may account for the extra oil.

If you are concerned about coolant or fuel contamination then drain some oil and smell it.  You should be able to smell any fuel.  If there is any coolant, it will settle to the bottom, as it is lighter than oil.  If the engine was run recently the oil and coolant will mix and appear milky.  If the oil is darker than new oil then my first postulation is advanced, i.e., the old oil was not completely drained.  

The chance that coolant leaked into the oil is nil.  No coolant galleries intersect any lubrication lines.

Carburetor floats have nothing to do with oil.  A difference of 0.67 Grs in one float is not cause for replacement.  Indication of a bad float would be a rough running engine. 

Even if the fuel pump failed, fuel will not flow anywhere unless the engine is running.  I have not taken a fuel pump apart but I do not think it possible for any significant amount of fuel to get into the engine from the pump.  Again, if so, you should be able to smell it.

Next time you change oil, consider purging the system to make sure all oil is drained.

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Dear AuntPeggy and Ed,

Thanks for your prompt replies and valuable thoughts.

When I changed the oil four months ago I thought I did it properly: I ran the engine to warm up the oil then switched it off, rotated the propeller after switching engine off, opened the oil tank from the bottom and gave time to the oil (still warm) to drain, then I changed the oil filter, replaced tank bottom cap and filled the oil (a little less than 3 litres).

I didn’t rotate the propeller while the tank was empty of its oil, and I wouldn’t suggest doing this because it might insert air in the circuit which would be a pain to chase afterwards.

Good to know that 0,67Grs difference Is not important enough to replace the floats. Nevertheless, now that I took off the float chambers I will replace the gaskets.

Any additional thoughts welcome.

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A little update:

Today I changed lubrication oil, oil filter, floats and float chamber gaskets and ran the engine but didn’t fly.

Engine ran smooth and nice for twenty minutes at 2200rpm then five minutes at 3000 rpm. No leaks from float chambers or from oil tank.

 I kept the used oil to measure how much it was. There is no fuel smell or anything strange in the used oil.

The only thing that I now suspect is that someone in the hangar might have rotated propeller opposite wise and inserted air in the oil circuit. Could that be a possible cause of the dramatic overflow I got?


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