French fry smell from a diesel engine isn't always a good sign

River Park · 2026-03-02T05:16:13.751022+00:00

I was at the shop yesterday and a customer's truck smelled like a fast food joint. Turns out he tried running it on used cooking oil without proper filtering, and now the injectors are completely clogged. Are more people trying this kind of thing, or is it just my area?

violaramirez7mo ago

Wait, how much filtering is even enough?

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emmalewis7mo ago

My biofuel experiment turned my car into a mobile fryer.

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sandra_carter7mo ago

That "mobile fryer" situation is exactly the problem. That smell means the oil is breaking down and leaving a gummy, sticky residue everywhere it touches. It coats the inside of the fuel lines and the injector nozzles, and when it gets hot in the engine, it basically turns into varnish. You might get away with it for a little while, but then the engine starts running rough because the fuel spray pattern gets all messed up. It's a total pain to clean out.

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the_drew7mo ago

Feel for @emmalewis, that varnish buildup is a nightmare to fix once it sets in.

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