viscosity question...

Hey all,

Just need a clarification re: motor oil viscosity... (yes I am a BITOG member, and couldn't find a clear explanation)

Currently running a 5w40, 95 cSt @ 40 degC (100F) 15.5 cSt @ 100 degC (212F)

I interpret the "5w40" as at 40 degC the oil has a viscosity of a 5 weight, but at operating temps (e.g. 100deg C), it has the viscosity of a 40 weight oil heated to 100deg C: 15.5 cSt; significantly thinner than at 40deg...

e.g. @ 100 C the 5w40's viscosity is equivalent to at straight 3 or 4 weight oil when the 3-4w is at 40 C. (according to Redline data for a 2w and 5w @ 40C)

Thanks!

The ratings are nebulous at best. I can't recall the actual temps, but for instance:

5w30 means that it acts like a 5 weight oil at 32 degrees F (I think) and acts like a 30 weight oil at XX degrees F.

Both of the numbers are weights, not temperatures. The "w" stands for winter.

curtis73 wrote: The ratings are nebulous at best. I can't recall the actual temps, but for instance: 5w30 means that it acts like a 5 weight oil at 32 degrees F (I think) and acts like a 30 weight oil at XX degrees F. Both of the numbers are weights, not temperatures. The "w" stands for winter.

You're a better man than I for even trying. I couldn't make sense of the original post.

To make it even more confusing, they're actually not measuring the same thing. Here is a pretty decent explaination:

http://www.ideas4ag-ed.com/uploads/3/7/0/4/3704787/stan_toepfer_understanding_motor_oil_viscosity.pdf

On top of that, many people don't really believe that these measurements matter as much as HTHS and VI. You can easily have a 0W30 that acts like a 5W40, and vice versa.

I've stopped trying to understand it and just run M1 in my street cars and Red Line in my race cars (or M1 if I am out).

robert

Just switched our cooper to 0w40 M1 as it is the only domestic product that meets the correct BMW spec. the 0 part worries me a little, but seeing the refernce to the VI and HTHS reassures me. A little.

There is no reason to be worried about the "0 part". It's a good thing. You want good oil flow when the engine is cold, that's when most wear occurs! M1 0W40 is one of the better oils you can buy and is used by many many race teams, it ought to do fine for you!

robert

my '94 Miata loves that stuff

My air compressor loves the 0W mobil one. It would trip the breaker on cold days even if you spun it by hand when turning it on. Switched to 0W mobil and never worrie about it just flip the switch and bump bump bump up it starts.

I have been using 0W-30 oil for years. Worked just fine. A quality synthetic that is not any of those previously mentioned.