Enlighten me. What exactly does XXw-XX mean. I now the latter number is the viscosity (higher being more viscous) and the first is wieght. What is wieght? Molecular wieght? If so doesn't that mean that the higher the number the more atoms are in one molecule of oil? I know that viscosity plays a big role in the climate you drive in but what about the wieght? What factors influence the weight choice?

 

Found elsewhere on the Internet:

 

So what does for example 10W-30 mean? It meets the SAE low temp requirements and has a viscosity of 10? what about the 30? I thought that was the viscosity?

 

Also located on "the net":

I'm not sure about the "W" standing for "winter", but it makes sense.

I would add that I used to use straight SAE 30 oil when I lived in Central America. It was 65-85°F year round. It never got cold enough for me to be concerned about getting cold (and thicking a straight-weight oil).

In sum, both numbers are the viscosity of the oil, but at different temperatures (0°F and 210°F). The first number ("--W") when the oil is cold, the second when it is hot.

Oil with only one number will be that viscosity at all temperatures. In other words, it'll be too thick at colder temperatures, hence the dual rating. Neat, uh?

Does this make sense?

EDIT:
To answer your question "What does 10W-30 mean?" -

When the oil is 0°F, it will act like a 10 weight oil, and when the oil is 210°F, it'll act like a 30 weight oil.

[This message has been edited by Stuart Moss (edited August 04, 2001).]

 

In reality, the base stock of the oil is in fact SAE 10W (ISO 32, or SUS 150 viscosity) and has viscosity enhancers to prevent thermal breakdown to the point where it will be similar to SAE 30 oil up to a given temperature (280°F). Of course it will ACT like 10W oil because it truly is 10W oil. The viscosity improvers wear off the molecules quickly and the "SAE 30" - like action is soon gone, so you are left with marginal 10W oil in the crankcase. This is another reason why it is very important to change mineral oil regularly.

Another tidbit of information, SAE 10W oil is the exact same viscosity as SAE 75W gear oil. That's not a typo - 10W = 75W. If you understand that the SAE system of rating lubricants is over 100 years old, you'll understand why it is really so meaningless and vague. Oils everywhere else in the world are sold by SUS viscosity and ISO viscosity - a system that is truly relevant. The only market that is stuck to the meaningless and intentionally confusing SAE system is the automotive market.

If you analyze what your favorite oil REALLY is, you might go shopping for something different. SAE 10W viscosity is the lowest grade I would use for anything, and I park cars in -35°F temperatures, outdoors in full exposure, overnight, every year. 10W30 Mobil 1 works fine for me. 5W and 0W oil might be great for french fries and tapping fluid, but not MY engines.

Synthetic oils actually "cheat" the SAE rating system because their viscosity is so stable over a wide temperature span, a SAE 10W oil rating is actually satisfied with a heavier base stock oil, more like 300-350 SUS (ISO 68). Once the engine (and oil) are heated to operating temperature, the mineral oil is woefully inadequate at a true viscosity of ISO 32, while the ISO 68 synthetic oil already has a distinct viscosity advantage. As the heat gets greater, the mineral oil suffers thermal viscosity and breakdown while the heavier synthetic just starts getting less viscous. At the extremes, the ISO 68 will still pump down to -57°F and fully lubricate and survive at 350°F. Mineral oil is already smoking and turning to carbon at 325°F, and is way too thin to provide adequate lubrication film strength well before that point. Under those conditions, it is basically a coolant used to flush the worn metal off the bearing shells and cylinder walls, since the only lubrication is the metal molecules themselves.

I hope you got the answer you needed.

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Later,
Vader
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"Let the bodies hit the floor!"
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Will 5W-30 Mobil 1 retain its 30 weight properties longer than mineral oil, or will the viscosity improvers deteriorate in much the same way? I've always used 5W-30 with no problems, but I could be convinced to switch to 10W-30 if Mobil 1 5W-30 behaves the same as mineral oil with respect to this one particular property.

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Jethro,

You've proven your knowledge and abilities countless times in your advice and ideas. If you are having good success with 5W30 Mobil 1, I'd say stick with it.

I've done a substantial amount of research on lubrication, particularly synthetic, since it's my butt if a piece of capital equipment fails. Unless a lube system is a loss-type (where none of it is returned to a sump for re-use) or the equipment has a significant oil leak or consumption rate, everything gets synthetics. The extra cash is well worth the extra uptime. Some equipment won't even run on mineral oil because of the extreme conditions. A 4,400 PSI nitrogen compressor would last about five minutes on the finest mineral oil (O.K., maybe seven minutes), but goes 2,000 hours between synthetic oil changes. Call me "brainwashed" if you will, but using synthetic lubricants in industrial equipment since the mid-'80s has given me a little room to speak.

The 5W-30 Mobil 1 you are using really isn't anything like 5W mineral oil. The SAE crankcase ratings are devised somewhat similarly to SUS and ISO viscosity ratings, then skewed to a number that really means very little. On the surface, one might presume that SAE 20W oil is twice as viscous as SAE 10W oil. In realitiy, it isn't even close. 10W is only 1.42 time a viscous as 5W, and 20W is only 1.43 times that of 10W. As soon as you get to straight SAE viscosity numbers, the scale has little relevance to real viscosity cup measurements at all.

As I stated earlier, the synthetic "cheats" the SAE system since it will flow through the viscosity cup at the same or better rate than a mineral oil at 0°F - the point where SAE "W" ratings are specified. Never mind the fact that the base oil is actually viscosity rated under both SUS and ISO scales (more realistic scales) at something more like a SAE 30 oil. At 0°F, "5W" Mobil 1 has a SUS time of less than 100 seconds - just like SAE 5W mineral oil. The cool thing is that it also is less than 100 seconds at -30°F, whereas 5W mineral oil has exceeeded 300 seconds. And at 210°F, the 5W mineral oil drops like a cheap tramp's pants (about 16 seconds), while the synthetic still maintains a sixty second drain time. THAT, my friend, is stable viscosity.

In a nutshell, the "5W" synthetic is possibly just a little less viscous than SAE 30 mineral oil at moderate test temperatures (210°F), but stays at that viscosity way down to butt-freezing cold. The 5W synthetic (which is probably really the equivalent of SAE 30) is not likely much different than "10W" synthetic, just slightly less viscous, and labelled to satisfy all those people who don't understand the rating system but absolutely insist on something that says "5W" on the can, regarless of what it is. Many people are afraid of using anything except what the manufacturer recommends, and every car made since the '90s specifies 5W-something on the fill cap (mostly for corporate fuel economy numbers). If you read any owners' manual, the oil recommendations change as the temperature does. For me, as long as the oil is suitable for pumping and lubricating at a temperature that is much lower than I'd ever expect, I'll go with the highest viscosity number for best protection at higher temperatures.

Some engines may sit outside in very cold temperatures and lose all their heat (mine do), but ALL engines (even those that get really cold) get started, get warmed, and have to operate at normal temperatures under normal loads. The 0W might be great for getting you started, but you'd better keep the engine speed under 3,000 RPM once the oil temperature has reached normal.

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

Vader is on a roll tonight! Thanks for the info and I feel much better now. I guess I won't get rid of 8 5W-30 M1 jugs in the basement just yet , but I probably will start running the 10W-30 M1 in the summers at least. Actually I have been experimenting with 15W-50 M1 right now, since it's in the 90's here often this time of year. My only concern with the 'ol redcap stuff is that the oil pressure will remain high enough to invoke the filter bypass, but I'm not sure what the GM pressure spec on that is.

Good call on the 0W oil too, and I'd also add that 5W-20 I've been seeing around lately to the dukey list (Ford, I think, recommends it). Maybe good enough for lube to keep in the nightstand drawer, but not in my trailer queens .

 

Trailer queens? Still ROFLMFAO!!

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Later,
Vader
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"Let the bodies hit the floor!"
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Just how I like my cars and women .