Alon c90 oil change

here is a real simple thing to do, drain the oil, remove the dipstick, take a flashlight and look inside, you should be able to see the drain valve. if there is still oil in the tank, remove the drain valve completely and see if the rest does not drain.

That is strange. But if there's still oil showing on the stick after letting it drain overnight, that pretty much narrows it down to an obstruction around the drain hole.

I'm imagining a layer of sludge that has formed a crater around the drain hole but is acting like a dam keeping too much oil in the sump.

If you don't have a bore scope, I would make a long, flexible whisk out of safety wire. (Make it long enough that it CAN'T fall in) The nice thing is, anything you pour into the sump doesn't contaminate the rest of the engine, so drain it as usual then pour in a couple quarts of solvent. Mineral spirits or xylene are best, or even kerosene or 100ll will work just beware of fumes. Then reach in with your special whisk and stir up any crud and sludge then open the drain. Keep stirring while you drain and if anything nasty comes out repeat as necessary.

None of the above solvents should damage the engine. Xylene and mineral spirits are commonly poured into the cylinders and then compressed to push through and clean up piston rings... then the oil is changed and any remaining traces are harmless. In fact they tend to clean up hydraulic lifters in some cases. Our oil is always contaminated with 100ll from piston blowby anyway.

You can also run a magnet rod down there to look for stray parts. It's amazing what you might find in an oil sump.

I change the oil hot. After flying I’ll stab the drain tube up from the bottom of the cowl. I do an oil sample halfway through the stream to send off to Blackstone and leave the tube attached to the quick disconnect overnight. I pull the spin on oil filter and leave it to drain overnight before cutting it open.

The thing that worries me is I still show 1quart on the stick after letting it drain overnight. Pulling the QD doesn’t get anymore oil out, and I’m only getting like 1 3/4 quarts out through the drain.

I've only got two ideas for this one...

1. If you're running the engine and then checking the dipstick or changing the oil while everything is still warm, there may be a surprising amount of oil "hanging out" up in the engine.

10-20 minutes after running my C85, the dipstick will read about 1.25 quarts less than the true amount. After sitting overnight all of the oil is back in the sump and I get a true reading. So... I do my oil changes cold. It drains painfully slowly but I do get more oil out.

2. With the plug or quick drain fitting removed, stick a bent piece of safety wire up into the hole to check for obstructions or sludge causing a standpipe effect. Alternately, the next time you drain your oil, run a borescope down into the sump through the filler neck.

Even after pushing the tail of the aircraft all the way to the ground with the drain hose connected. I got a grand total of 1 3/4 quarts out of the engine. The owners manual says don’t take off with less than 2 quarts. I removed the quick drain plug and no additional oil came out and still read 1 quart on the dip stick.

I will post more pictures tomorrow.