Why is running 50 wt oil okay when it asks for 40?

[jmo]

Hey guys,

One thing I've always been curious about is people running 50 wt oil when it calls for 40wt? why is this being done? Any down sides?

Thanks,

JMO

[KTM525]

Well.. depends if you ask for something like 15W40 or only W40. With the Multigrade oil, you get a larger range to temp you can use it. A 10W50 stays less viscous in low temp and more viscous in high temperature then a 15W40. The downside, its more expensive and you don't need it. More important is: use a quality oil that meets the spec from the engine manufacturer and not something cheep. There are some difference in the additive in the oils.

[xrichard]

If you read through the bobistheoilguy "Motor Oil University" pages, you might be convinced to use lower viscosity oil. Sometimes higher viscosity is recommended solely to reduce oil consumption--not a good reason, IMHO.

[jmo]

I am only referencing the operating temp viscosity, so for an engine requiring 10w-40 for example they would run 15-50.

[jmo]

Interesting read, makes me think I should run 0W-40 synthetic in my Excalibur instead of 15-40 Dino...