My old man told me to never trust a 'quick fix' additive for injector knock, and I should have listened

I had this 6.7 Powerstroke with a nasty knock that wouldn't go away. A guy at the parts counter swore by this 'Diesel Doctor' additive, said it would quiet it right down for $40 a bottle. My dad, who wrenched on semis for 30 years, always said those bottles are just expensive bandaids and to find the real problem. I bought the bottle anyway, poured it in, and the knock got softer for about 50 miles. Then it came back worse than ever. Turns out I had a failing injector cup, which the additive just masked for a bit. Ended up costing me over a grand to fix it right after I wasted time and money on the snake oil. Anyone else have a story about a 'miracle' fix that just made things worse?

3 comments

3 Comments

beth_butler753mo ago

That's a tough lesson to learn, but your dad was spot on. Read a story in a truck forum about a guy with a Duramax using a similar product for a miss. It just gummed up the whole fuel system when the real issue was a tiny piece of trash in the line. Those additives can sometimes change the sound for a minute, but they never fix the broken part. It's like taking aspirin for a broken arm, you might not feel it but the bone is still snapped.

emma_hart3mo ago

Exactly, it just masks the problem. I learned that the hard way with an old carburetor that needed a rebuild, not another bottle of miracle goop.

blakem822mo ago

Honestly, I see it a little different. Tbh, sometimes those additives can be a good first step if you're trying to diagnose something on a tight budget. Not saying they fix the real problem, but they can tell you if it's even worth digging deeper. Ngl, your story shows what happens when you rely on them too long, but that Duramax story kind of proves the point too - a quick test can tell you a lot. My dad always used a cheap bottle of diesel purge to see if an injector was actually bad before he tore anything apart. It's all about knowing when to use it and when to just fix the damn thing.