So everyone keeps saying you need to let a diesel idle for 5 minutes before shutting it down. That's old advice and it's HURTING your engine.

I see it all the time on forums and in shops. Guys let their trucks idle for 5 to 10 minutes after a hard pull before they kill the engine. This was true for the old mechanical injector pumps but modern common rail systems with electronic injection don't NEED that cool down like that. In fact I watched a guy at my shop in Tulsa burn out his turbo seals last year doing exactly that. He would drive in hot idle for 8 minutes then shut it down. His VGT turbo had oil coking issues at 80k miles. I know this because I pulled the turbo myself and found the oil passages partially blocked. The real trick is to let it idle for 30 to 60 seconds tops. Anything more is just wasting fuel and heat soaking the top end. Has anyone else actually torn down a turbo and seen the damage from long idling?

2 comments

2 Comments

wendygrant27d ago

Man, you hit the nail on the head about "heat soaking the top end" because that's something I never hear people talk about when they're just parroting the old 5-minute rule. I had a buddy with a 6.7 Powerstroke who insisted on letting it idle for ten minutes every time he came off the highway, and his valve cover gaskets were weeping oil by 60k miles. The way I see it, all that extra idle time just bakes the oil on the hot spots and cooks the rubber seals, doesn't it? How many people actually check their oil cooler temps after a long idle and realize the engine is actually getting hotter, not cooler?

hill.troy26d ago

Fair point, but I still idle mine a few minutes after a hard run and haven't seen issues.