Changing the oil in your general aviation aircraft can be tricky.
That’s because many oil pans and drain plugs are “perfectly” located above the nosewheel mounting system or some other frame structure so that it is almost impossible to get to the drain plug without burning your hands, as well as spilling oil all over the frame and floor.
A quick drain valve helps some, but still many mechanics will wait until the engine cools off to remove the cowl and try to drain the oil. And they still spill some oil and need to clean up the plane and the floor around it. This requires extra time and expense for cleaning solvents, as well as the chore of disposing of the cleaning solvents.
Many years ago, a friend of mine came up with a system to suck the oil out of the dipstick tube. It is a relatively simple system and should work well for aircraft.
The main component is an electric motor-driven hydraulic pump. The pump needs to be a gear pump because vane pumps may not pull enough vacuum. The motor should be at least ¾ or 1 horsepower.
On the intake of the pump, connect a hydraulic hose at least 10 feet long and ½ inch or larger diameter. Next, remove your dipstick and measure the width.
This next step may take a little trial and error. You need to get several diameter Teflon or other oil resistant tubes and determine the largest size that will go all the way into your dipstick tube. Now compare the length of your dipstick to the tube — the tube needs to be a little longer.
On the end of the hydraulic hose you will need to install a reducer coupling to connect it to the Teflon tube. To the outlet of the pump, install a 90 pipe elbow, then a 12-inch pipe, another 90, a 6-inch pipe, and another 90. The end should be pointed down. A length of pipe may be needed to reduce splashing. (You may also wish to install a pipe T on the inlet and put a vacuum gauge in the open port.)
If you install the system on a dolly or cart, you can move it to a plane anywhere in the hangar or on the apron.
To change the oil, the aircraft should be flown long enough to get the oil temperature up to normal. Now put the plane wherever you choose and remove the dipstick.
Note the reading, as this will tell you how much oil you should expect. If you have an eight-quart sump and the dipstick shows a quart low, you will expect seven quarts to be pumped out.
Place a container under the outlet and push the Teflon tube into the dipstick tube. Turn on the pump. You may need to insulate the hose as it can get very hot. Keep pumping until you start sucking air. If you have installed a vacuum gauge, it will drop to zero when it starts to suck air. Move the tube around to ensure you have picked all of the oil up.
Next check the volume of oil in your container. It should be close to what your dipstick indicated. It may be helpful to make marks on the side of your container at one-quart increments.
The first few times you do this you may wish to open the drain plug for peace of mind assurance, but normally you will find no oil left. Once the oil is removed, you need to replace the filter and/or check the screens before refilling the crankcase.
What are the advantages of changing oil this way?
The first is that you can pump the hot oil out immediately after shutting down the engine. This eliminates the sludge from settling out.
It also keeps you or your mechanic from burning your hands, and it eliminates the oil spill on your aircraft and on the floor around it.
And, in most cases, it will reduce the time and cost for your oil change.
I found it to be a messy job even with a quick drain and hose until I developed this setup:
I got an appropriate length of aluminum tubing about the size of the quick drain outlet tube, a short piece of hose that fits the quick drain, and two adjustable stainless hose clamps.
The piece of hose goes on the end of the tube. A clamp is tightened to securely attach it there so it can’t pull off.
The tube and hose are pushed up onto the quick drain outlet. The second clamp is tightened to hang on to the drain fairly tightly but not real tight. That serves two purposes. The first is so that you don’t have to hold onto the tube while the oil is draining.
To drain the oil put a container on the ground under the engine and tube. Insert the tube up to the quick drain and push the hose onto it – and then push more to open the drain and drain the oil into the container.
You don’t get burned because you don’t have to fool with using your hand to open the quick drain.
When through and no oil is still dripping, pull the tube down and if the tension on the clamp at the end is correct it the hose will pull the drain closed.
Consider letting the oil drain into the container through a fine stainless mesh screen. That can be inspected for particles coming out with the oil.
Also use a completely clean container. Let the old oil sit for a long time, then drain the container and see if any fine particles remain in the bottom. If you use a non ferrous container you can also use a magnet to see if any particles are iron or steel.
Of course the cowl should be removed and all the other stuff done, too.
Removing the oil filter can also be messy.
Just loosen it enough that it is only hand tight but not dripping, then put a large plastic bag like a 1 gallon ziplock over it (and the filter adapter if any), and unscrew it the rest of the way. Continue to hold the bag with the filter there until no more oil drips into it. Have some paper towels or old rags handy.
All this is pretty fast, simple, and easy. Cheers!
I agree with the other commenters.
During a 50 hour oil change, besides changing the oil and filter, I do a compression check, check for loose/ missing hardware, oil leaks, carb. cable connections, wire/ hose routing for chafing….etc.’look at everything’.
Some recommend removing the cowling every 10 flights to check the security of everything.
As much as I respect Ben and normally agree with his knowledge and insight there are a couple of flaws in this one. First we have “casually acquired” a 3/4 hp electric motor…and pump… and mandated that the oil change be done within reach of an appropriate electric source. Sourcing all the bits of hose, Teflon included, is again a “casual acquisition”. That stuff doesn’t grow in trees. IF I were doing oil changes on a commercial level this might pay. As our Mooney mechanic points out above there is more to the “oil change” than just swapping newer dinosaurs for old. That far more extensive look around three to four times a year or less… is often the time we find things that need minor attention before they become failures.
As for convenience I almost always have a quick drain to work with in by birds and (in my semi retirement) my select few customers. I NEVER advocate leaving a hose attached. The C150 that went down 20? years ago after the stiff old hose opened his drain valve in flight cured that but sticking a hose on even a warm engine has never been a real finger burner. The hose can be led anywhere to a clean white bucket. It’s also a requirement to pull and inspect the oil screen/filter so the upper cowl ought to come off anyway and I’m going to dribble a bit of oil here that encourages cleaning the engine and compartment as well. As today’s generation would say JMHO LOL. After 52+ years of flying and restoring and fixing ‘em my opinion may not be so humble”… 😎. I still respect your input Ben and read EVERY column but it is fun to have a dialogue as a result. I believe THAT is almost more important than just the passing of knowledge. Thank you !
I prefer doing this the old way because with the cowlings removed you can inspect all kind of other things and make sure that everything else is OK. Our increasingly geriatric airplanes are not like modern cars on which things almost never come apart, fail, get loose, leak and so on.
Example – I helped a ’66 Mooney owner do an oil change and discovered a deep nick in the copper oil pressure line which goes to the gauge. The copper tube was old, brittle and the nick was a great stress raiser. One of the securing mounts (tie points) for the tube was also failed (split), so the line was waving in the breeze. If we had not taken off the cowling and looked around, we’d never have seen that. The oil line looked to be hours away from breaking, which would let all the oil out, and the noise would stop . . .
Take the time and get dirty, hand cleaner is lots cheaper than hospital bills.
(Now I’m toast for sure, I’ve disagreed with Ben Visser!!!!)
Agree. I changed oil at 50 hour intervals with our rental, flight school and Part 135 aircraft, including our regular customer’s aircraft. Following the Cessna maintenance manual, there are other things to inspect and check at those intervals (50 hour, 100 hour, etc.), and that can’t happen if the engine isn’t uncowled. Besides, how else can an oil filter be replaced, or an oil screen be removed and cleaned?
An old grizzled, cantankerous mechanic I used to work with once told me, “There are no shortcuts to good maintenance “. I never forgot this axiom.
An even greater part of your Mooney story is who gouged the line, split the retainer, and placed it back in service?
Don’t think that occurred on it’s own between the last annual and this oil change at 25-50 hours.
If you can’t keep from making a mess when changing engine oil using a quick-drain valve, then perhaps you shouldn’t be changing your own oil.
The worst oil changing experience I can recall is with the rear engine of a C337. Nevertheless, I’d run an appropriate hose through the hole provided in the lower fixed cowl, and guide it up through the center of the muffler, and onto the quick drain. For other engines, I had an old piece of rain spout to run the oil into it bucket. There is ALWAYS a way, if you just look and think a bit.