Tired of people saying you gotta run a diesel hard to keep it clean

I hear this all the time at the shop from the older guys. 'Drive it like you stole it' or 'let it eat' to blow out the carbon. Honestly I think that's just a myth that causes more wear. I rebuilt a 6.7 Cummins last year from a guy who always drove it hard on the highway. Valves were toast and the rings were cooked. A steady drive at 1800 RPM with a good load does the same cleaning without hammering the internals. Anybody else see more damage from this old school thinking?

2 comments

2 Comments

barbara_kim2mo ago

You ever actually run a diesel long enough to watch the EGTs and see what's happening? Because I have, and hard running doesn't clean anything. It just heats up the oil faster and cooks the turbo seals. Steady load at operating temp handles the carbon without bouncing off the rev limiter. I've pulled apart engines from "drive it hard" guys and they're always worse than the highway cruisers. Carbon buildup comes from short trips and cold idling, not from babying it.

aaron_gonzalez2mo ago

Take @barbara_kim's point about oil temps and turbo seals and think about the fuel itself. Modern diesel in the US has way less sulfur than it used to, which actually changes how carbon forms and burns off in the combustion chamber. So what worked to clean things on a 90s 7.3L Powerstroke might not even apply to a newer common rail truck with a DPF.