Truck runaway engine - GIF

**schuylergrace** · Feb 4, 2023, 08:19 PM

I don't have any experience with a runaway diesel, but I always wondered why they don't just shut off the fuel and maybe, block the air intake. I've seen a lot of these where folks either intentionally or accidentally grenaded a diesel, and it's quite the sight!

**hemmjo** · Feb 4, 2023, 09:40 PM

Originally Posted by schuylergrace

I don't have any experience with a runaway diesel, but I always wondered they don't just shut off the fuel and maybe, block the air intake. I've seen a lot of these where folks either intentionally or accidentally grenaded a diesel, and it's quite the sight!

Runaway diesels are caused when there is an alternative source of fuel. Most commonly bad bearing in a turbo pumping engine oil into the intake. Shutting fuel off does no good as there no way to shut off the alternating fuel. The air intake on most diesels is typically not easily accessible. In addition, when it happens most people freak out as it is a scary situation. It is also very risky to even be close to an exploding engine.

There are emergency shut-offs systems available, which shut off intake air, but again, the vast majority of diesel powered devices do not have one installed.

One example;

Truck runaway engine - GIF-screen-shot-2023-02-04-11.37.23-pm.png

**schuylergrace** · Feb 4, 2023, 09:57 PM

Originally Posted by hemmjo

Runaway diesels are caused when there is an alternative source of fuel. Most commonly bad bearing in a turbo pumping engine oil into the intake.

I hadn't thought about that, even though several folks mentioned the turbo bearing oil being a cause. I always assumed something malfunctioned to allow the primary fuel to go into the engine unregulated. But my only real experience with diesels is with our old International Harvester tractors back home. They prolly would have died if somebody got near them with a turbo!

Thank you for the elucidation!

**mr mikey** · Feb 5, 2023, 04:28 AM

Sometimes the fuel is off and the engine is running on crankcase oil, your right about blocking the air flow. Hopefully you can access the intake before it destroys itself. Most diesels are low rpm's, when it runs away rpm's can double what its rated for so parts will break. The boss will not be happy.