OK so if this is true about oil:

"Multi-weight oils (such as 10W-30) are an invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature. This page from the Sci.Electronics.Repair FAQ offers the following very interesting description of how the polymers work:
At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot."
http://auto.howstuffworks.c...ion/question1641.htm

Why would anyone want a thicker oil at startup (10w30) that is going to be the same 30 weight consistency at running temp as 5w30, when 5w30 flows better at startup when most engines get the most wear?
And while on that topic would not then 0w30 be best when it is cold up north?

[This message has been edited by 2.5 (edited 04-14-2010).]

You do not want to thin of oil, or else it is easy to get pushed out of the way, like it is not even there.
That is why it is always best to go with the manufacturer's suggested oil type on newer cars. There is a whole lot of engineering that goes into oils, and even more that goes into engines that use the oil and clearances and pressures require a certain weight.

[This message has been edited by LitebulbwithaFiero (edited 04-14-2010).]

The reason why I use 10w30 over 5w30 is because there are less polymers in the oil. Less polymers means there is more lubricating oil.

As long as you have the correct oil for the temperatures that you are operating your vehicle, then a 5w or 0w winter rating should not matter.

This is all my opinion. I'll see if I can dig up some links that I have read about the subject over the years.

quote Originally posted by 2.5: Why would anyone want a thicker oil at startup (10w30) that is going to be the same 30 weight consistency at running temp as 5w30, when 5w30 flows better at startup when most engines get the most wear?

Your reasoning is correct, but I'll try to answer your question directly.

First, the rest of this discussion does not generally apply to synthetic motor oils. The viscosity range of synthetics is engineered into the molecules and no additional polymers are needed to provide the high viscosity index (VI) desired. (The VI is simply a measure of the multiweight properties of an oil; generally, the higher the VI the better. A 5W30 will, by definition, have a higher VI than a 10W30.) For all practical purposes, the VI of synthetic motor oils does not degrade in service.

A 10W30 "conventional" (i.e. simply refined) motor oil starts out with a base viscosity roughly equivalent to a 10W oil, and then polymers (VI improvers) are added to achieve the equivalent of a 30 viscosity at operating temperature (~210 F, 100 C). It's easy to see that a 5W30 oil will probably require more polymers to be added to the base stock to achieve the desired 30 viscosity at operating temperature when compared with a 10W30 oil.

There are two basic problems with VI improver polymers, though. First, these polymers are not lubricants, so you can only add so much of them without starting to compromise the lubricating ability of the oil. Second, and perhaps more important, the polymers degrade (i.e break down) with time and mileage. The primary mechanisms are oxidation and mechanical shearing of the long polymer molecules, and as the polymers degrade the viscosity of the oil at operating temperature slowly reverts toward the native viscosity of the base stock. A 10W30 reverts toward the equivalent of a 10W viscosity at operating temperature, and a 5W30 reverts to the equivalent of a 5W viscosity; neither trend is desirable. What this means, though, is that a 10W30 motor oil will maintain a higher average viscosity (at operating temperature) as it ages in service when compared with a 5W30 oil. This is one important reason (but not the only reason) why conventional motor oils require shorter change intervals than synthetics.

For further information, I highly recommend this series of articles by Dr. A.E. Haas. They are highly readable, and he goes into a lot more detail than I have here.

[This message has been edited by Marvin McInnis (edited 04-14-2010).]

Thanks guys, Marv so what you are saying is in regard to conventional oils, some people would choose a 10w30 over a 5w30 and sacrifice a better flow at startup, in order to get better lubrication and longer oil life?

I realize this is different for each engine, and newer engines are very specific in their viscosities required. I noticed for example in a 1998 Grand Prix's 3800 v6 for example what sounds like lifter noise on startup when using 10w30 and could not hear it when using 5w30.

quote Originally posted by 2.5: ... what you are saying is in regard to conventional oils, some people would choose a 10w30 over a 5w30 and sacrifice a better flow at startup, in order to get better lubrication and longer oil life?

Few people actually understand how oil works, and in particular what the viscosity numbers mean beyond "a higher number is thicker."

"Some people" would probably choose a 10W30 over a 5W30 thinking that the 10W30 is better because it doesn't "thin" as much at high temperatures, and that a 5W30 is only appropriate during winter or in colder climates. Most people think that "higher is always better" when it comes to oil pressure, and a 10W30 will definitely give you a higher oil pressure at startup than a 5W30. I doubt that consideration of oil life vs. viscosity change even enters into their decisions.

Me? GM specified a 5W30 motor oil for the V6 in my Fiero, and that's what I use. I use a synthetic (Mobil 1) because I believe that synthetics provide better lubrication under all conditions, and using longer oil change intervals makes the synthetics cost competitive vs. high quality conventional oils. As with most things, I tend to buy oil based on overall value rather than price alone.

[This message has been edited by Marvin McInnis (edited 04-14-2010).]

Yeah probably alot of people just choose one because they saw it on tv. I guess I am trying to get a clear view of the right reason to ever choose a 10w over a 5w starting viscosity. Other than maybe an engine that needs more than 5w at statup, like a racing engine maybe? It would seem avoiding more polymers, thus having more lubricants is the reason.

One thing that I have noticed is that some manual transmissions use gear oil while others use regular engine oil. I even had a 87 Toyota Celica 5 spd that used ATF but that is a different matter. Why would some manufacturers recommend one or the other?

quote Originally posted by 2.5: ... maybe an engine that needs more than 5w at statup, like a racing engine maybe?

The clearances in most road racing and track racing engines (I don't know about quarter-mile engines) are set up for operating oil temperatures of 250 to 300 F ... much higher than for street use ... which makes start-up viscosity even more critical. In fact, many world-class racing engines (e.g. the Olds Aurora-derived Indy engines) require that the engine oil be pre-heated before starting, otherwise engine damage may result from the oil being too thick.

quote It would seem avoiding more polymers, thus having more lubricants is the reason.

If you are using a conventional (non-synthetic) oil, that might be a good enough reason.

So a 0w30 would have even more polymers in it.

Since nearly every new car requires 5w30, cars seem to be being built requiring the oil with less lubricants in it. Do you in any circumstance advise an oil additive to add more lubricants back? Slick50, Prolong, Duralube, etc.

In the heat of the summer (highs of 26 Celsius, lows of 15 Celsius), I use monograde SAE 30 (if available). Don't care about cold temps - might as well use oil that maintains its hot viscosity between oil changes, and it's usually cheaper too.

When the weather gets colder, then I switch to 5W-30.

[This message has been edited by pmbrunelle (edited 04-14-2010).]

quote Originally posted by 2.5: So a 0w30 would have even more polymers in it.

Conventional oils, yes. Synthetic oils, no.

quote Do you in any circumstance advise an oil additive to add more lubricants back? Slick50, Prolong, Duralube, etc.

I generally do not, but "any circumstances" covers a lot of territory. The only blanket exception I might make today would be a zinc/phosphorus additive (e.g. ZDDP or TCP) for a flat tappet engine with aftermarket, high rate valve springs. Moly (molybdenum disulfide) is another excellent extreme pressure and boundary lubricant, but it works best when applied to surgically clean parts before assembly; even the finest moly powders tend to be removed by the oil filter. Other than those two, I wouldn't use any other additive without first knowing what's in it, and how much ... and that information is a closely guarded secret of most of the "Snake Oil" manufacturers.

FWIW, to the best of my knowledge the "secret ingredient" in Slick 50 is superfine Teflon powder. Even DuPont, who makes Teflon and owns the trademark, does not recommend its use in motor oil. There were even several aircraft incidents years ago due to engine failure that were later determined by the FAA to have been caused primarily by the presence of finely divided Teflon particles in the oil.

[This message has been edited by Marvin McInnis (edited 04-14-2010).]

quote why would anyone want 10w30 over 5w30?

Cuz the 5W-30 makes my wife's skin break out in a rash.

Jim

quote Originally posted by Marvin McInnis: FWIW, to the best of my knowledge the "secret ingredient" in Slick 50 is superfine Teflon powder. Even DuPont, who makes Teflon and owns the trademark, does not recommend its use in motor oil. There were even several aircraft incidents years ago due to engine failure that were later determined by the FAA to have been caused primarily by the presence of finely divided Teflon particles in the oil.

Interesting info, PTFE right? They must have tried real hard to cover that story up. Slick 50 is even an added ingredient in some Quaker State oil now.

GM etc use 5W-30...

GM etc uses One Spec for year round protection. One spec is easier for car makers and most owners. Use what ever makes you happy.

Use 5W-30 or 10W-30 in summer doesn't matter for CONUS and Hawaii. Alaska has cold temp in Summer...

code:

---

If lowest expected outdoor temperature is: 
0°C (32°F) use 5W-20, 5W-30, 10W-30, 10W-40, 20W-50
–18°C (0°F) use 5W-20, 5W-30, 10W-30, 10W-40
Below –18°C (0°F) use 5W-20, 5W-30

---

quote Multigrade oils such as SAE 5W-30 and 10W-30 are widely used because, under all but extremely hot or cold conditions, they are thin enough to flow at low temperatures and thick enough to perform satisfactorily at high temperatures. Note that vehicle requirements may vary. Follow your vehicle manufacturer’s recommendations on SAE oil viscosity grade.

Code and Quote Source: API doc Engine Oil Guide (English) page 2 http://www.api.org/certific...categories/index.cfm

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