A basic question probably asked before

[tjw]

One of the comments I've often heard about synthetic oils is that they are "thin". Am I correct is assuming all oil viscosities are graded the same. A synthetic 10-40 has the same viscosity at 100 and 200 degrees as conventional 10-40 oil. Why the reputation for "thinness"

 

[1maniac]

As I understand it the opposite is true. A quote from Redline's site in reference to their synthetic 10w40

quote:

---

Features a thicker oil film at operating temperature than a petro-based 20W-50.

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[Pablo]

Perceived (by a human) thiness is not equal to measured viscosity.

 

[Al]

They'll be pretty close at those temps.

 

[haley10]

Some of the thin "reputation" probably comes from the popularity of Mobil 1 products. They tend to be at the thinner side of the scale and have a huge market share.

It's not a universal truth that syn's are thinner.

 

[Schmoe]

Look at the specs. All oils are "different." There is a range of viscosities for any weighted oil. Like the M1 comments, may hear some on here say, including me, that a 5W-30 is a "thick" 20 weight. All that means is that the 5W-30 is on the low side of the 30W viscosity chart, so it would appear to be a high 20W.

 

[TooSlick]

A synthetic oil of the same SAE grade WILL be thinner at room temp, in fact it will be thinner whether you pour it out @ 0F or 100F. The key that synthetic lubes don't thin out as rapidly when heated to their normal operating temp. So at the 100C/212F standard test temp used by the SAE, they fall in the same viscosity ranges as conventional lubes. At temps >> 212F, most synthetic lubes are in fact THICKER than their petroleum counterparts. This is a function of their higher viscosity index, ie the change in viscosity measured between 40C and 100C....

xw-20, viscosity is 7.7 to 9.3 Cst @ 100C
Example: Amsoil 5w-20 is 8.8 Cst, so it's at the high end of this range.

xw-30, viscosity is 9.3 to 12.5 Cst @ 100C
Example: Mobil 1, 0w-30 is approx 10 Cst, so it's at the lower end of this range.

xw-40, viscosity is 12.5 to 16.5 Cst @ 100C
Example: Amsoil 15w-40 is approx 15 Cst, so it's in the middle of this range.

xw-50, viscosity is 16.5 to 20.5 Cst @ 100C.
Example: Redline 20w-50 is approx 20 Cst, so it's at the high end of this range.

If you were to pour any of these formulations out of the bottle at room temp, they would flow easier than a petroleum oil of the same SAE grade, hence the illusion that they are thinner ....


Tooslick
www.lubedealer.com/Dixie_Synthetics

 

[T-Keith]

I think it's another myth, coming from people trying to explain why they have leaks. People swear that it is because synthetics are slipier or thinner and can get out of the engine easier.

-T

 

[Jeffrey Behr]

quote:

---

Originally posted by tjw:
One of the comments I've often heard about synthetic oils is that they are "thin". Am I correct is assuming all oil viscosities are graded the same. A synthetic 10-40 has the same viscosity at 100 and 200 degrees as conventional 10-40 oil. Why the reputation for "thinness"

---

I believe that reputation was initially for their pourability when very cold. That is, they're not as thick (as dead-dino stuff) at, say, -20°F. People who don't know much then applied that to all synthetic oils at all temps.

In fact, synthetic oils ARE thinner at very low temps but they're also thicker at very high temps.

And indeed all oils of the same label-viscosity number are thicker or thinner, as the label-viscosity number includes a range of measured viscosities. One 10W-30 could be considerably thicker or thinner than another 10W-30. Check this chart for the ranges.

 

[TC]

Pennzoil 10w-30: 67.0 (40C), 10.5 (100C)
Pennzoil Syn 10w-30: 61.6 (40C), 10.5 (100C)
Quaker State 10w-30: 69.1 (40C), 10.5 (100C)
Quaker State Syn 10w-30: 61.9 (40C), 10.5 (100C)
Kendall GT-1 10w-30: 67.2 (40C), 10.1 (100C)
Kendall GT-1 Syn 10w-30: 65.7 (40C), 10.5 (100C)

Seemingly modest differences within this small sampling.