michaeljones•1mo agoMost Upvoted

Blew my mind when I learned engine oil weight numbers aren't actual measurements

I was talking to an old timer at a parts store in Nashville last month. He told me 10W-30 doesn't mean 10 weight at 0 degrees or whatever I always thought. Turns out the W stands for winter and the numbers are viscosity ratings from a test. Found out the SAE actually sets these standards back in the 1910s. I've been turning wrenches for 12 years and never knew this basic fact. Anybody else get surprised by something simple like this way later than they should have?

2 comments

2 Comments

lily2301mo ago

That winter rating part always messes with people's heads. The SAE standards go back further than most folks realize, I remember finding out the numbers come from how fast the oil flows through a specific sized hole at certain temps.

ray_mitchell1mo ago

Man, you're totally right. I used to think the winter rating was just some marketing thing they slapped on the bottle. Like, who actually tests oil in the snow, right? But once you explained how it's all about the flow rate through that tiny hole at specific temps, it clicked for me. It makes a lot more sense now why picking the right oil matters so much in cold weather, especially for older engines that don't like thick stuff.