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DRAGON88

Why so thick? 15w-40

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DRAGON88

I've been reading a lot about oil lately, different types of bases and additive packs etc. I currently run Castrol (German) Syntec 0w-30 in my A4. Essentially the 15w stands for the oil's viscosity or pumpability at low temperatures. a 15w oil is pretty thick at startup which is less than ideal for lubricating our motors. The myth is that something like a 0w-30 is actually thinner than a 15w-30, when in reality it is the same when warm, it just pumps better and causes less wear when the engine is still cold.

Oil type... Thickness at 75 F...Thickness at 212 F

Straight 30...... 250......................10

10W-30............100......................10

0W-30..............40 ......................10

Straight 10........30....................... 6

Optimally we want about 10cS (centi-strokes) at 212* as you can see both the 10w30 and the 0w-30 are 10cs when warm. The difference being that at ambient temperatures, the 0w oil is much closer to our desired viscosity.

Any thoughts or opinions on this issue? I'm thinking that I'll start using a 5w-40 this summer and see how that works out.

http://63.240.161.99/motoroil/index.html

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electricjohn

What they are really specifying is a 40 wieght oil. Why the 15w is beyond me. I guess it's better than straight 40.

Also remember most of us use our boats in the summer only, so 15w would flow no problem. It also has the least amount of V.I. of the multigrade 40 wieghts. If you are concerned about flow when engine is cold, go to a 10w-40, or even Mobil 1- 0w-40. Just remember oils with alot of V.I.'s sheer out faster than those with less. Malibu is even calling for 20w-50 now in the Hammerhead motor (IIRC).

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RTS

And keep in mind our engines normally operate at lower temps than the 212* a car may see.

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skislut

uh -- it's "centistokes"

while I didn't really read all of 101 thru 109, I did look over the data table and it's pretty impressive -- even printed out a copy for my shop wall.

I skipped down to Mobil 1 as that is what I use -- interesting that the 0W-40 has a higher visc. at 40 C than 10-30. Guess I won't buy that anymore for my 4X4 with the high output oil pump that I run in the winter.

I was more interested in the high shear viscosity - why they gave it at 150C is beyond me -- it would have been killer to show it at 100C to compare the 30-40-50 weights in resistance to thixotropy -- which is data you want. I would think that would show you flowability out of the bearings, the lower the number the better.

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Big Mac
What they are really specifying is a 40 wieght oil. Why the 15w is beyond me. I guess it's better than straight 40.

Also remember most of us use our boats in the summer only, so 15w would flow no problem. It also has the least amount of V.I. of the multigrade 40 wieghts. If you are concerned about flow when engine is cold, go to a 10w-40, or even Mobil 1- 0w-40. Just remember oils with alot of V.I.'s sheer out faster than those with less. Malibu is even calling for 20w-50 now in the Hammerhead motor (IIRC).

All of the 15W40 diesel oil are blended from group II base stocks. Consequently the need for viscosity improver is minimal and shear stability excellent. That didn't used to be true, but it's the reason so many auto mfgrs spec warranty oil changes at 6000 miles now.

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chathamsolutions
uh -- it's "centistokes"

while I didn't really read all of 101 thru 109, I did look over the data table and it's pretty impressive -- even printed out a copy for my shop wall.

I skipped down to Mobil 1 as that is what I use -- interesting that the 0W-40 has a higher visc. at 40 C than 10-30. Guess I won't buy that anymore for my 4X4 with the high output oil pump that I run in the winter.

I was more interested in the high shear viscosity - why they gave it at 150C is beyond me -- it would have been killer to show it at 100C to compare the 30-40-50 weights in resistance to thixotropy -- which is data you want. I would think that would show you flowability out of the bearings, the lower the number the better.

I totally disagree. The flowability of muffler bearings is crucial when considering the high-throughput of a hexagonal sheared semi-transparent visc. But you're premise is wrong.

What confuses me is the fact the Mobil 1 doesn't have the thixotropy gains that an obvious 30-40-or even 50 would have. Even if you mixed them all together, ran them through a centrifuge for homogenization, you'd still have brown sludge - able to handle 212F in any Germ, Jap, Korean, Detroit, Czech car out there. But would you have the centistokes to deal with a high visc. (+ - 10k <12) at low temp (40C)?

You shouldn't have printed a copy for your wall, you should have printed it and used it as toilette paper.

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WakeGirl
What they are really specifying is a 40 wieght oil. Why the 15w is beyond me. I guess it's better than straight 40.

Also remember most of us use our boats in the summer only, so 15w would flow no problem. It also has the least amount of V.I. of the multigrade 40 wieghts. If you are concerned about flow when engine is cold, go to a 10w-40, or even Mobil 1- 0w-40. Just remember oils with alot of V.I.'s sheer out faster than those with less. Malibu is even calling for 20w-50 now in the Hammerhead motor (IIRC).

Last I heard was that they were calling for straight 40w & sometimes 50w in some cases (just to clarify, this is with the newer 383ci Hammerhead - the older 350ci Hammerhead was plagued by other problems, but low oil pressure alarm was not one of them). They did say that 20/50 is fine to use as well, but that was never actually documented (except for a phone call by stewart as I recall to Indmar :)).

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skislut

You think I'm going to take anyone seriously who signs off their post with a reference to Scott Hamilton??

:lol:

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chathamsolutions

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tuneman

O.K., I'll give some input, but I don't know if it will help:

Multigrade oils, like 15W-40 are just that: multigrade. The W viscosity rating is at 0 degrees Celsius. The other is at 100 degrees Celsius. So, for example, 15W-40 acts like a straight 15 weight oil at 0C and acts like a 40 weight oil at 100C. The higher viscosity is needed at temperature since the metal parts of the engine "shrink" (metal shrinks as it is heated).

Our boat engines usually run no hotter than 160F. Why? Because salt within the water will come out of solution near that temperature. (It's more critical for saltwater cooled boats.) We don't want to plug stuff up.

The engine manufacturers have all done extensive testing to find out the best oil to use for each engine. The Indmar engines love a 15W-40, so I wouldn't mess with it, unless you want trouble. A lower viscosity oil, like 5W-40 will shear faster that 15W-40 and that's the main reason for using the latter.

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RTS
Our boat engines usually run no hotter than 160F. Why? Because salt within the water will come out of solution near that temperature. (It's more critical for saltwater cooled boats.) We don't want to plug stuff up.

Wow..that's interesting. I always wondered why our engines ran so "cool". I always though it was because they had a constant supply of cool water, so why not run cool.

Thanks for the info...you learn something new every day Thumbup.gif

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DRAGON88
O.K., I'll give some input, but I don't know if it will help:

Multigrade oils, like 15W-40 are just that: multigrade. The W viscosity rating is at 0 degrees Celsius. The other is at 100 degrees Celsius. So, for example, 15W-40 acts like a straight 15 weight oil at 0C and acts like a 40 weight oil at 100C. The higher viscosity is needed at temperature since the metal parts of the engine "shrink" (metal shrinks as it is heated).

Our boat engines usually run no hotter than 160F. Why? Because salt within the water will come out of solution near that temperature. (It's more critical for saltwater cooled boats.) We don't want to plug stuff up.

The engine manufacturers have all done extensive testing to find out the best oil to use for each engine. The Indmar engines love a 15W-40, so I wouldn't mess with it, unless you want trouble. A lower viscosity oil, like 5W-40 will shear faster that 15W-40 and that's the main reason for using the latter.

I think you have a few things confused. First, metal EXPANDS when it gets hot, it contracts or shrinks when it gets cold.

Second a synthetic (To my knowledge all 0w oils are synthetics.) 0W-40 or 5W-40 will see less sheering and viscosity loss than a standard 15w-40 mineral base. Also A 0W-40 is not a lower viscosity, at operating temperature it is the exact same viscosity. (in many cases such as the German Syntec 0w-30 the opposite is true. 0w-30 is actually actually closer a 40 weight oil.) The only time that a 0w-40 would be thinner is at ambient temperature where we WANT the oil to be thinner. Simply put the 0w-40 will thicken less after you shut the motor off. Running a 0w-40 is definitely not asking for trouble at all, if anything it will extend the life of the motor by being more pumpable when a motor is cold.

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tuneman

Oops, yeah, I meant expands. Too many hours at work and not enough ridin' time.

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