Imagine you are pre-flighting your King Air, checking the oil and on one engine the oil is off the stick! What do you do? For many, the first instinct is to dump a couple quarts in that side and check the stick again. Just make sure you have plenty of rags in the aircraft because there’s a good chance the oil you just dumped in will be all over your flaps and gear doors at the end of your trip. It’s what happens when you over-service the oil.
Oil is the lifeblood of any engine, so when it’s suddenly off the stick, it gets your attention and rightly so. But before you add oil, I suggest to try motoring that engine for about 30 seconds and check the stick again. Chances are you’ll find the oil back on the stick, at the level you typically expect for that engine. If so, you’re good to go.
What you have is a minor oil migration problem on that engine which can be easily remedied at the next Phase inspection. Until then, whenever you check the oil on that side (when the engine is cold, as in before a flight), you’ll want to motor that engine briefly before checking the stick. Then put it on your squawk list for your next maintenance visit.
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, after only 20 minutes your engines are still piping hot; and even though you may have shut everything down and buttoned everything up, there’s still baggage and passengers, instructions for the line guy, maybe a rental car or just a long drive home. Let’s face it, at the end of a trip, checking the oil on a hot engine is not very practical.
Far more important in my book is just checking the oil, period! (Those of you out there who never check your engine oil – ever – I’m begging you to start now.) I don’t care whether you check it post-shutdown on a hot engine or if you check it before the first flight of the day, on a cold engine. Just keep doing it that way consistently.
In addition to simply verifying oil is present, you are discovering the preferred oil level for each of your engines.
Engine Oil Levels
I’ve mentioned engine oil levels many times in this column, but I get calls on this subject all the time, so it bears repeating: The PT6s on your King Air are not identical twins. They each have their own quirks and tendencies, including the oil level they prefer. I’ve found many a PT6s that run consistently at 2-3 quarts down. (To be abundantly clear – that’s between the second and third hash marks below Max Cold on the stick, on a cold engine.) Some engines stay at 3 or even 3.5 quarts low. Many times there is a disparity between your engines – the left side is happy at 2 quarts down, but the right side prefers 2.5 down. Learn the oil level for each of your engines.
More on Migration
As an engine cools after running, the oil collects in the oil tank located above the oil filter housing. However, 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 the oil on that side. But take a look around – check the floor, look inside the cowl – if you don’t see obvious evidence of an oil leak then it’s still inside the engine. Motor it for 30 seconds and check the stick again.
Here’s what happens: During every phase inspection the oil filters and chip detectors are pulled, inspected and reinstalled. Some oil filters are less cooperative than others. If they’re tough to get out, they’re tougher to get back in. The process of removing and reinstalling a stubborn oil filter can jostle the oil filter housing ever so slightly. If that happens, the O-rings between the filter housing and the engine case can lose a bit of their seal. If you have an oil migration problem, these O-rings are the likely culprits. But 30 seconds of motoring gets the scavenge pump to move the oil back into the oil tank, and then it shows on the stick.
The funny thing about Pratt & Whitney’s recommendation, if you only check your oil levels when the engines are hot, you would never know whether or not you had an oil migration problem. It could go undetected for years.
Mass Migration
Oil migration is an oil leak inside the engine. The good news is that the engine is still full of oil and will operate properly.
If you opened your engine cowl and saw oil dripping out of the compressor inlet, you have reason for more concern. This indicates a larger amount of oil is leaking out of the tank and accumulating inside the engine where the bearings are. When the oil reaches the level of the shaft, it leaks out. You want to get that addressed.
Hopefully you are checking your oil faithfully. If it is suddenly off the stick on a cold engine, just motor that engine for 30 seconds and check again. You should be good to go.
Note: A similar article with the same name ran in the October 2015 issue.