Why is HD-30 thicker than 10w-30 when hot?

[Hemi426]

Most straight 30s are 11.5 at full temps while most 10w30s are in the 10.5 range. I know HD-30 uses no VII. Does that have some thing to do with it? Thanks

 

[Astro14]

Not really, 30 is a range of 10 - 13 at 100C...they're both 30s, but the HDEO is just created a hair thicker because it has a different intended use...I am sure a tribologist can answer more technically, but that's my simple man view...

 

[mechanicx]

I wished I could find the graph but an HD 30W or HD 10W30 specifies a higher minimum HTHS of I think 3.2 while non HD 10W30 is 2.9 iirc. So to get there HD has to start on the high side of a 30 grade especially not having vii. So the viscostiy index could be considered a factor but more importantly along with HTHS.

 

[JHZR2]

Yeah, just a more robust oil for a more robust application.

 

[unDummy]

Don't automatically assume that a straight-weight oil doesn't have VII/VM type additives.

 

[chevrofreak]

Originally Posted By: unDummy
Don't automatically assume that a straight-weight oil doesn't have VII/VM type additives.



VII are not allowed in monograde oils.