Just read in a fleet maintenance report that a single clogged DEF injector can drop fuel economy by over 15% on a modern rig

Found this stat buried in a quarterly review from my company's shop in Boise, and it's got me wondering what other small, easy-to-miss issues have a massive impact on MPG that you guys have come across.

3 comments

3 Comments

the_anthony2mo agoMost Upvoted

Fifteen percent seems like a stretch for one small part. Those reports often use worst-case numbers from lab tests. Real world driving rarely hits those extremes.

brian_smith62mo ago

Wait, 15 percent from just one injector? That's a whole lot of money just leaking out the tailpipe. Makes you wonder what else we're driving past that's killing our fuel numbers. I had a trailer with a dragging brake that felt fine but cost me nearly two mpg before we caught it. Those little things add up so fast it's scary.

janarivera2mo ago

My old man ran a fleet out of Spokane for years. He had a truck that kept losing power on hills. The shop checked everything, even the DEF system. Turned out to be a tiny crack in the turbo intercooler pipe you could barely see. It was leaking boost pressure. The drop in mpg was way bigger than you'd think, like 12 percent easy. Makes me see where @the_anthony is coming from about lab numbers, but real world stuff like that hidden leak can get pretty close.