Figured out I was using the wrong oil weight for my 12-valve after a buddy checked my cold start smoke

Had this old 1996 12-valve that's been smoking like crazy on cold mornings for maybe 2 years. Changed injectors, did a pop test on them, even tried a different fuel filter. My buddy who works on these for a living came over last week to help me diagnose something else and he looked at my oil jugs. Said I was running 15w-40 year round. He told me to switch to 5w-40 in the winter and it's night and day on startup smoke. Had no idea oil viscosity made that much difference on a mechanical engine. Anyone else learned something simple like this way later than they should have?

3 comments

3 Comments

angela72834m ago

Yeah, "felt like an idiot after spending like 300 bucks on parts he didn't need" is basically how it goes. It's like that thing where you're trying to fix a squeaky door and you oil the hinges three times before realizing the frame is just slightly out of square. We get real focused on one part of the problem and forget the simple stuff right in front of us. I've done it myself with my truck and also with stuff like a slow draining kitchen sink - bought a new disposal and everything, turns out the pipe had a chunk of lard stuck in it. The simple fix always feels like a trick you should've known. It's a good reminder to check the basics first before you start dumping money into fancy parts.

dakota_miller935h ago

So my buddy had pretty much the same thing happen on his 7.3 Powerstroke. He'd been running 15w-40 religiously for years and had crazy white smoke on cold mornings, figured it was glow plugs or injectors. Turns out his truck just really wanted 5w-40 when it got below freezing. He told me he felt like an idiot after spending like 300 bucks on parts he didn't need. It's wild how much a little change in oil can mess with these old mechanical diesels.

thomas.river5h ago

Did you ever see that test someone did comparing cold start times with different oil weights? @dakota_miller93 haha