Q's about M1 5w30 visc.

[speedtc]

There is always talk about M1 5w30 being a thinner 30 weight. Is that because of it's viscosity index or it's 40*/100* C. viscosity?
I see it talked about frequently and i've always wondered.

 

[racer12306]

i believe that when an oil is considered to be a thinner 30 weight they mean the viscosity at 100* C, as with a thicker 30 weight, like gc to be at 100* C aswell.

 

[farrarfan1]

Keep in mind that viscosity is measured in ranges. A 30 weight can be anywhere from a minimum of 9.5 cst to a maximum of 12.49 cst at 100c.Mobil's website lists SM M1 5W30 as having a viscosity of 11.3 at 100c.The SL version was listed at 10 cst as is the current SM M1 10W30.This is, as I understand it, an average and can vary from production lot to production lot.11.3 cst puts it slightly higher than the exact median (10.9 cst)range of 30 weights.

 

[speedtc]

Thanks. As i was browsing M1 5w30 seems to be not as thin as people think. It's right htere with synpower, platinum, syntec, and Q power in the 5w30 range. The higher valvetrain noise with 5w30 seems to be a characteristic of the oil's makeup and not viscosity. At least that's what my un-trained eye sees.

 

[Volvohead]

As stated, the advertised viscosity of a multivis is only that measured at two specific temperature points. However, the actual viscosity between and OUTSIDE of those two points (its viscosity curve), is rarely linear.

An oil's VI is merely the amount of measured viscosity change just between those advertised temperature points.

Most folks' engines do not operate at exactly 40 or 100 degrees C.

As a weight grade includes a range of values, any precision is further clouded. A "thin 30" is an oil whose actual viscosity at 40 or 100 is on the lower end of the scale for a "30" grade.

So you can also have some 10W-XXs flowing much better than some other 5W-XXs at some colder temperatures outside the advertised points, or the opposite may happen at higher temps. For instance, M1 10W-30 tends to have a lower viscosity than their 5W-40 at temps around 0 degrees F.

The advertised viscosity weights are merely a rough guide of how the lubricant should generally behave, and little more.

 

[RF Overlord]

speedtc, Mobil 1 WAS as thin as people thought, until the new SM stuff. SL was 10 cSt @ 100° and 56 cSt @ 40°, whereas SM is listed as being 11.3 and 64.8, so yeah, it's not as thin anymore...I'm not happy about the change, especially the increase in viscosity at 40°, so I was thinking of cutting it with a couple of quarts of 5W-20 at my next change.

Interestingly, Mobil 1 EP 5W-30 is the same viscosity as the old SL Mobil 1.

 

[speedtc]

Thanks.