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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 recommenda- tion, 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.
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