Good day,

I currently fly an aircraft with a 200hp IO-360 Lycoming engine. I notice that after an oil change the oil remains clean/clear until somewhere between 25-35 hours and then turns dark rather quickly; always within that 5-10 hour mark. Any other experiences with this issue? Is this the reason for the "25 hour Oil Change"?

Cheers

I am not an a&p so take this with a grain of salt. (or maybe call up lyc or a real a&P)

The color of the oil is not directly related to its ability to lubricate and protect an engine. Different oils in different engines seem to darken at different times. As long as you stay in the lycoming recommended changing interval's you should be fine.

Your oil should turn a nice chocolate brown if everything on top is in good shape in 20-30 hrs. If you have compression leaks it will turn black.

When you say turns dark is it dark brown or dark black? If its black and your getting abnormal amounts of carbon in your filter when you cut it open then your top end is suspect.

If it stay's clear for 25 hours, your fine. Some oils, like Exxon Elite have a more aggressive detergent package than others and will turn color sooner. What Scout say's is correct about color. My IO-520 is a Continental factory overhaul and it's oil turns brown. I have both a C-85 and an IO-540 with Millenium cyl's and both of them's oil turns black indicating blow-by, but both of them have very good compression checks? I think the Millenium's have a lot of "choke" in the cylinders and this is why their oil turns black. I've decided not to worry about it, other than the black oil color, they both run like Swiss watches., well the C-85 like a rough Swiss watch anyway.

My O-320-A2D starts to turn brown around 25-30 hours too. All the analysis and cutting the filter show everything is good. Lowest compression at the last annual was 78.

What do most of you use for oil change intervals? My airplane is flown a couple times a week and we typically do 40-50 hours before a change.

I use Aeroshell 100W Plus.

Chris

This is an interesting discussion. My Rotax, which is quite a different beast from the big iron most of you fly, also dirties it's oil at about the 30 hour mark. Because the crankcase and gearcase share the same oil, and there is a slip clutch with linings in there, and because I use 100LL some of the time, I use a semisynthetic motorcycle oil and change at 50 hours. My lowest cylinder pressure is 190 psi. (10.5:1 compression ratio)

tom

They say 50 with a spin-on but that's a bit too long, and 25 (like with a screen) just ain't enough-- so I split the difference and run 'em 40 with the spin-on.

Eric

The reason the oil is changing color is because it is picking up solids from the engine to the point where the oil is opaque, ie: no longer clear. That is a good thing--that is precisely what detergent oils are designed to do. lJust because the oil has picked up a bunch of stuff, however, does not necessarily mean it's no longer doing its job.

My philosophy is that oil is one of the cheaper things we do with airplanes. I change oil more frequently than the manufacturers recommend. I change oil and filter at 30 hours, or if I'm on a trip, maybe 40.

I also use ASL Camguard to help protect and clean my engine.

MTV

My O360 use to stay clear 35 plus hours. I changed it and the filter every 50 hours. I use the Aeroshell 100W summer and 80W winter. It was like that though 1800 hours, then because of an insurance paid for tear down look see, I decided to pay the difference and have a complete OH with new cylinders, pistons, etc.

Ever since that OH, it turns dark after 10-15 hours. The analyisis checks come back ok. I still change oil and filter at 50 hours, which is about every 3-4 weeks.