The International Cessna^® 170 Association

Look, I like to warm up the oil so it drains faster and I'm not there all day waiting for a thicker slurry to decide it's time to make its way out the plug hole. And I really can't stand putting the plug back in while a single drip is hanging on the the plug threads. Yet I know there is still old oil that can not be drained short of an overhaul.

And I would be lying if I told you I haven't considered the engine warm up and oil circulation an opportunity to stir up and suspend contaminates in the oil to be drained.

What kind of contaminates are we speaking of. Anything heavier than the oil has already settled into every knock and cranny in your engine after every shut down. No avoiding it. What might keep you up at night is thinking how much of these contaminates, once settled, are actually resuspended during engine operation?

You could always fill the case with quarts of diesel fuel after draining. Run it, drain it and run it again dry to make sure you get every morsel of oil out before you put the new stuff in. Wouldn't want to leave any dirty oil in those pump gears, journals or between the bearing surfaces (who wants dirty oil on their bearings?

BTW, please don't do this.

The drain plug in my Lyc O-360 is too far forward to get complete draining on a tailwheel airplane. I once tried raising the tail and got maybe another ounce of oil to slowly drain. Definitely not worth the work. For me, that is. Each owner should do whatever seems right to them. After this, we can discuss preheating ...

The reason to change oil often is to get rid of contaminated oil. Fresh oil will dilute whatever did not drain previously. It's the method which has worked for the last 50 years just fine.
I agree that getting it hot lets it drain faster and also helps rid the engine of suspended contaminates.

Opening all the hoses, letting it drain overnight or for long periods.... while that might make your mind rest easier... that comfort will evaporate after you've found you've introduced the possibility of a loss-of-pump-pick-up...and find you've started an engine that won't develop oil pressure quickly. You might try it several times and the engine might still not develop oil pressure and you have to find a way to pre-pressurize the system. How is that comfortable-feeling working out for you now?

Accept it. A little dirty oil will remain. History has shown that is not harmful if we do oil changes sufficiently often.

ALWAYS check the screen if you still use one. EVERY TIME.

A buddy of mine was apparently not taught to do that and when he brought is C175 to my house for some work we did an oil change, and when I started to pull the screen he asked, "What are you doing now?";

After he saw his suction screen was almost COMPLETELY BLOCKED with carbon he nearly had a stroke. It was unbelievable the oil pressure had not fallen yet.

(If you are one of those people who have converted to a spin on filter.... congratulations. If you are one of those who throw the filter into the trash without cutting it open... you are not much better off than those who still use screens. At least they are seeing what their engine is doing before it fails at night or over water or over downtown. I'll bet Bruce can add something to this after finding metal in his oil screen.)

Checking your screen or the inside of your filter is hundreds-of-times more useful/informative in most ways and a lot cheaper than oil-analysis (which I consider a general waste of good flying money.)

gahorn wrote: I'll bet Bruce can add something to this after finding metal in his oil screen.)

Checking your screen or the inside of your filter is hundreds-of-times more useful/informative in most ways and a lot cheaper than oil-analysis (which I consider a general waste of good flying money.)

I have always pulled my screens every oil change. It is simply not that hard to do. Had we not, we would have found the screen full of metal on the next change. And we may have damaged expensive parts in the mean time.

BTW besides all the oil galleys and bottoms of the valve covers, you should see how much oil is inside the front of the crank that does not come out. I wouldn't be surprised if all told there was better than half quart and as much as a quart of oil that is not drained no matter how long you let the pan drip.

As an engineer, I can tell you that draining the oil hot is more effective. As said, at least some of the crud is suspended in the oil. I always pull the screens for inspection and cleaning. I'd rather find any metal early on before it's done more damage. Of course, if you have a filter, that should be cut open for inspection too. Just IMHO.