Thread: Best Oil
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Old 11-20-2012, 08:45 PM   #34
Back Road Runner
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Join Date: Apr 2004
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Location: Minnesota
2004 Forester STI


Originally Posted by eg33GC View Post
I would never run 0w on an old G K or up to v6 205/7
Originally Posted by subi400 View Post
For what reasons???? Someones opinion

What you are not understanding here is that it is the operating temp that you are looking for in an oil. You want the best flow on start up hence the "0"w30, "0"w40 and then a good 0w"40" for best protection at operating temperature. There is a guy/vendor over on who uses a 20w50 racing oil but complains why it is soo expensive to do oil changes but won't listen to anyone else's advice on running like a 5w50 oil which is actually cheaper....

So, tell me why wouldn't you run a 0w something oil in one of those engines?


0 is the base weight, the starting oil, also the thickness when cold generally speaking although a 0w20 is thinner than a 0w30. Cold, the oil is MUCH thicker than it is hot. A 0 base weight cold is magnitudes thicker than a 30 weight, 40 weight, or even 50 weight oil when up at operating temps. What you're getting with the 0 base is a relatively "thin" and liquid oil at very low temps (although still very thick versus any oil heated). This gives you great cold weather performance.

The 30 is the relative viscosity when heated up to operating temps of the engine. A straight 30 weight, 10w30, 5w30, and 0w30 all end up around the same thickness when heated to operating temps. The difference between them is the additive package they use to achieve that. A 0w30 takes a more advanced additive package than a 5w30 or 10w30 to keep it from thinning out so quickly. The additive package keeps it "thick" (relatively) when it is heated up.

You have the option to step from a 10w30 to a 5w30 or a 0w30 to gain improved cold weather operation. As you go down in base weights, the oil stays thinner colder. The oil remains a liquid and pumpable down to very low temps (for a good synthetic, somewhere around -60F).

For hot weather, performance, or loose or worn engines, you can run a thicker oil hot in order to minimize oil consumption and potentially wear. To reduce consumption and wear, you go up in hot viscosity so you go from a 5w30 to a 5w40 or 5w50. Again, a higher hot viscosity generally runs a more advanced additive package to keep it thicker when heated. The most advanced additive packages will typically offer the widest viscosity index (VI), basically how flat the curve is from cold to hot or how wide of an operating range the oil is good for. The widest options currently produced are 0w50 and 5w60 oils, and yes both exist. The highest VI I've come across is Eneos' 0w50 and basically offers the best all weather and all use operation available.

Now there's a trade off to picking a thicker hot viscosity. The oil pump can only do so much. As you go thicker you reduce flow quantity. Yes, you get more protection from shear, but you get less flow. Less flow means more heat build up, and this too can destroy engines. Typically a looser built engine or worn engine has enough slop in the parts to retain high volume flow with a thick oil. A very tight motor may end up with too little flow to properly cool bearings, and you can get localized failure that way.

What's most ideal? I don't know, I haven't the foggiest clue, and I have never nor seen specific tests to measure this. My rule of thumb for personal use is I run as thick as I need to keep consumption "normal," and by normal I mean 1 quart of oil per oil change. This may also include sport use as in I don't want to be down 1 quart after a race day if I can make that happen. Stepping to a higher hot viscosity is one way to achieve that. From my experience with a worn out 2.5L NA engine, I get roughtly half the consumption with each step up. If I lose a quart with 5w30, I will lose half a quart with 5w40 and only a quarter of a quart with 5w50. It's not scientific or exact, but it's a relative scale I've seen through my personal use. It also has been relatively brand independent, and I have switched some brands and switched between 5wX and 0wX too.
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