Hello, I'm new to the forum and diesel engines in general.
I bought my first diesel project - 2010 Mega Cab -Rolled Over. The engine started fine and idle wihtout problems but when I took the truck for a spin the engine got stuck on high RPM's 4,000 and wouldn't shut off even with the key off... It ran like that for 30 seconds and it died.

Now it won't start and the mechanic says that it blows air thru the oil filter. Based on your experience what could have caused the engine to rev up so high and stay like that even with the key off the ignitio?

 

It's called a "runaway diesel". It could be running on a number of things after the fuel is shut off (that's all the key does on a diesel, as there are no spark plugs to turn-off). One possibility is that it's ingesting oil through the intake side of the turbo, or it can even be running off anti-freeze through a crack in the block (strange but true). Blowing air through the oil filter is an important clue though, I'm sure somebody will know on here.

 

Indeed the engine's oil was all over the place on the engine compartment from being upside down after the wreck.
I assume some of the oil got inside the trubo and that's why it wouldn't shut off... Do you know how can I test each individual cylinder to identify a root cause for a repari!

 

The crank case breather is fed into the intake of the turbo which is a stupid idea unless it has been changed. With the truck being rolled the oil from the crankcase could find it's way into that pipe and into the intake of the turbo. You may have to remove the pre cooler and have it cleaned internally. One thing I would do is remove the crankcase vent from the turbo intake, there are a few solutions to this including using a piece of hose and routing it down into the frame area on the passenger side.