In having some ring-side conversation at the field one day, a pilot had mentioned he runs his engine “dry “ when he’s done flying for the day. Another pilot chastised him for this, and said he shouldn’t do that. I’d like to set the record straight… BS, BS, BS! Running your engine “dry” when you’re done for the day, is (in fact) the best possible thing you can do to prevent corrosion. And here’s why: First of all, you can’t literally run
a glow engine DRY. The fuel simply contains too much oil. The engine quits running
because there wasn’t enough methanol/nitro (the active part of the fuel) to sustain
ignition. HOWEVER there’s more than enough oil (the passive part of the
fuel) to lubricate the bearing surfaces until the engine completely stops running (even if
it’s running at full throttle). THREE things happen when you run a glow engine “dry” or below Ignition Capability: FIRST: it removes the fuel from the crankcase, lines, carb and tank. SECOND: it warms up the engine; a warm engine quickly vaporizes the remaining methanol and nitro in the crankcase. THIRD and most important: the fresh air passing through crankcase purges the remaining fuel vapors only leaving the oil film as the engine spins down to a stop. If you DON’T run it “dry”, you are leaving highly corrosive methanol and nitro methane through out your engine! Then you kill your engine by closing the carb, your crankcase has lots of active methanol/nitro in it, as well as well as solid fuel in the carb and fuel line. So you removed the solid fuel from the fuel tank. BIG DEAL! Your crankcase, carb, and fuel supply line are still loaded with active (and very corrosive) fuel. So then you put after-run oil in the carb and spun the engine over. Unless you spun the engine over enough to completely purge the crankcase, carb, and fuel line, you are not even remotely of the woods yet. And then there’s the cold engine. A cold engine won’t evaporate the active part of the fuel as quickly as a warm engine, so vapors stay in the crankcase for a long time. It’s these active vapors combined with air that destroy your bearings and other ferrous engine parts! If you use after-run oil and didn’t run it dry, or totally purge your engine you will end up with this:
This owner USED After-Run Oil
religously, but didn't purge or run it dry. The active vapors penetrated the
after-run oil and totally destroyed the bearings, crankshaft, camshaft, and rod along with
other misc. parts.
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