Old timer told me to warm up my diesel for 10 minutes every time

Guy at a shop in Phoenix said I had to let my 7.3 idle for a full 10 minutes before driving, even in summer. Did that for about 6 months until my buddy who's a fleet mechanic laughed at me. He said modern diesels don't need that unless it's below freezing, and I was just wasting fuel and glazing the cylinders. Has anyone else gotten bad advice from older mechanics that messed up their routine?

2 comments

2 Comments

black.beth1mo ago

Fleet mechanic actually explain why glazing happens at idle?

taylor_flores1mo ago

Oh man, YES. I had this happen on my old lawn tractor (a Cub Cadet, if that matters) and it drove me nuts. Basically, at idle you get that incomplete combustion where fuel and oil mix together and leave this sticky varnish on the cylinder walls. It builds up over time, especially if you let it sit and cool off after a short run. That glaze is like a slippery coating that makes the rings lose their seal, so you get that blowby and rough running. My mechanic buddy said to take it out and work it hard once in a while, get the engine hot enough to burn that gunk off.