Page 10 - August 2015 Volume 9, Number 8

Oil Migration
Imagine you are pre-flighting your King Air, checking the oil and the oil is off the stick on one side. After uttering the obligatory expletive, what do you do? If your first instinct is to dump a couple quarts in that engine and check the stick again, chances are you will be wiping oil off the flaps and gear doors at the end of your trip because you over-serviced the oil.
Oil is the lifeblood of any engine, so when it is off the stick, it gets your attention, and rightly so. But before you add more, try motoring that engine for about 30 seconds and check the stick again. If you find the oil back at the level you typically expect for that engine, then you are good to go. You have a minor oil migration problem that can be easily remedied at the next phase inspection. As long as you are checking the oil on a cold engine, you’ll want to motor that engine briefly whenever checking that side until the migration problem can be properly addressed.
Checking Cool or Checking Hot?
Pratt & Whitney says you should check the oil level on each engine within 20 minutes after shutdown; but in reality, who does that? First of all, the engines are still piping hot after just 20 minutes. And even though you may have shut everything down and buttoned everything up, there’s still baggage and passengers, instructions for the line guy, possibly a rental car, or maybe just a long drive home. Let’s face it, at the end of a trip, checking the oil on a hot engine is not everyone’s favorite thing to do.
Far more important in my book is just checking the oil, whether the engine is hot or cold. (Those of you out
8 • KING AIR MAGAZINE
there who never check your engine oil ... ever ... might want to pay attention.) Whichever way you choose to check the oil, whether it’s post-shutdown or before the first flight of the day, do it that way consistently.
In addition to simply verifying oil is present, you are discovering and then maintaining the oil level at which your engines like to be. I’ve found many PT6 engines like to run at between two and three quarts down. To be clear, on a cold engine, that’s between the second and third hash marks below Max Cold on the stick. Some engines stake their claim at three or even three-and-a- half quarts low. And many times there will be a disparity between your engines – the left side is happy at two down, but the right side prefers two-and-a-half down.
More on Migration
As an engine cools after running, the oil collects in the oil tank located above the oil filter housing. But if the oil is able to get around the housing and travel down to the accessory gear box and the bearing areas below, it will go there. Then you come along, checking the oil before your next trip and (surprise!) the oil is off the stick. It looks like you suddenly lost all of the oil on that side. But it has to go somewhere, so if you don’t have obvious evidence (such as a puddle on the floor and a mess inside the cowl), try motoring that engine for 30 seconds and check the oil again.
Here’s what happens: During every phase inspection, the oil filters and chip detectors are pulled, inspected and reinstalled. Some oil filters are difficult to get out and get back in. The process of removing and reinstalling a stubborn oil filter might jostle the oil filter housing ever
by Dean Benedict
Oil migration can cause an oil level reading to suddenly be “off the stick.”
OCTOBER 2015
MAINTENANCE TIP