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Just learned how much a single drop of DEF can contaminate a whole tank | Diesel Mechanics - Free To Speak

Just learned how much a single drop of DEF can contaminate a whole tank

I was reading an old service bulletin from Detroit Diesel about DEF system care. It said that just one drop of engine oil in a 55 gallon DEF tank can ruin the fluid's effectiveness and potentially damage the SCR system. I had no idea it was that sensitive. I've always been careful to keep things clean, but I figured a little splash wouldn't hurt. Now I understand why they push those special funnels and dedicated equipment so hard. It makes all the extra wiping and prep time feel worth it. Has anyone else had a truck come in with SCR issues that traced back to contaminated DEF?

4 comments

4 Comments

park.miles6mo ago

That Detroit Diesel bulletin is no joke. I once spent a whole afternoon trying to figure out a weird SCR code, only to find a tiny smear of grease on the fill neck from someone's glove. My own glove, of course. I felt like a real genius that day. It's crazy how something you can barely see can cause such a headache.

claire_grant346mo ago

Sometimes those tiny issues are the best teachers though, right? Makes you triple-check the simple stuff next time.

mary_nelson716mo ago

Reminds me of the time I chased an electrical gremlin for two days. Traced wires, swapped relays, the whole deal. Finally found a single strand of steel wool stuck in a connector block, probably from cleaning a terminal. How does something that small shut down a whole system? Makes you want to pull your hair out.

cooper.drew5mo ago

Man, doesn't it just drive you nuts? Tbh I had a similar thing with a crank sensor code that kept coming back. Spent hours on it, checking grounds and wiring. Ended up being a tiny piece of plastic shaving from when I'd replaced the connector, just sitting in a pin. It was barely even visible. Makes you feel crazy until you finally spot it.