Oil Pressure Issue?

RustyRatRod said

Well......sorta. The first number is the weight before the oil reaches operating temperature. Once there, it is the second number.

I have assumed for years that the "W" stood for winter, but it does not. At least from what I can dig up on the net. The best that I can find is that it means "when cold" or before operating temperature.

At least, that's what I have gathered from most of the oil sites.

So basically, if you have 20/50, it is essentially 50 weight because that's what it is when warmed up.

At least, this is what I have inferred from reading. I could be slam wrong.

Click to expand...

No you are close. The W actually does stand for Winter. The issue is all the WINTER grades are measured at different temperatures. And, just to make it difficult, API does NOT recognize winter grades above 25.

Let's take a 20 winter grade oil. Off the top of my head, IIRC, it acts like a 20 at 32* or colder. A 15 winter grade is measured at 20*. A 5 winter grade is down at ZERO again if IIRC correctly, but I am close.

One of the reasons I spend big money per quart of oil is I can run a 5w50 and not have an issue if I show up at the track and its 40*'s in the early morning, and where I live, it can be. Then you get a 50 when its hot. For my street stuff, I can use a 5w30 and drive it year round.

I'm old enough (probably RRR is too) to remember Castrol had a 10w50 way back in the day. It was a good oil, but due to the fact it was a mineral oil, it was very expensive to have that much spread between the winter grade number and the running temp number, so it was dropped. That was about the time I switched to synthetics so no bones for me. But other guys were pissed.