turbo's run a long time with no oil in them. Well, longer than you'd think anyway. It's not an instantaneous failure if it doesn't have oil in it yet, or after you shut it down. After engine is turned off, it's still got oil in it, pressure drops off within a few seconds. The turbo on the SVL's is so tiny that it stops within a few seconds of the engine being turned off. It never really loses significant oil until long after it's shut off.
However, coking can happen-it's a lot less common now than it used to be, mostly due to the change in engine oil formulation. But some folks still use the dirt cheap oil from Fred's and that might contribute to coking.
Normally the most common cause of turbocharger failures is lack of oil or contaminated oil during operation. Second most common is foreign debris entry (through the compressor) which eats up the compressor wheel and sometimes the housing. Dirt is the #1 foreign debris. Nuts and bolts, bits of the air filter, bits of stuff that came out of the airbox during filter replacement, all contributing to the same things.
Just an example, working on an old G1900 that used to belong to my brother. The frame is broken the deck is rusted, it's not really worth fixing. Engine runs fine and it does pull itself so it's mostly something to piddle with. I bolted an old Kubota (IHI RHB3 I think) to the manifold and ran some piping to the intake, sealed everything up and fired it up. No oil. I've run it for a good 30 minutes straight at full load, 4 psi (that's all it will do) boost with the blades on, and so far the turbo is still doing fine. I've done it multiple times, twice today actually. I'm thinking about making a different manifold to get the turbo closer to the head, maybe it'll make a little more boost and respond faster. But, it doesn't solve the fact that the turbo is just too big for it. BTW I can't tell a lick of difference in power, the only thing I notice is that the black smoke under load is gone. And note, I really don't care if the engine eats a compressor wheel, or if a turbine wheel exits the housing, or a seal goes south. The mower has no value but for scrap, and that's where it will go when the time comes.
