5W-10W30/40 or 15W40?

robison · Jun 27, 2005

There is an important reason for lighter oils that has been missed in this discussion.

In addition to lubricating your engine your oil is also responsible for cooling the motor. For example, oil spray cools the underside of your pistons. The oil spray is the principal thing transferring the heat load from the pistons into the block where the coolant passages transfer the heat to the coolant.

Thicker oils reduce the flow rate, sometimes by quite a lot. Modern 0-40 and similar synthetics are designed for rapid flow for improved cooling.

In addition higher flow rates reduce formation of sludge.

If you have modern a diesel engine that calls for a 5-30 oil it would be unwise to use a 15-50 instead for the reasons outlined above.

LBrown59 · Jun 28, 2005

( I can't point you at the previous thead, but I remember someone emailing Kubota and asking about their 5w-40 spec for tractor engines...and the reply was use 15w-40 as that is commonly available and they just had not got around to up dating thier manuals yet...

Four hundres hours later it seems to be working fine...in my engine... /forums/images/graemlins/smile.gif )

 15w-40 is all the local dealer carries

Schultz · Jul 1, 2005

OK, I just changed the oil in my Kubota and noticed that the Mobil 1 I had on the shelf was diesel rated and bracketed the 15w-30 that was recomended. I figured I was alright with the 0w-30. What's everyones opionion on 0-30 in a diesel.

familyman · Jul 1, 2005

At my 50 hour oil change, I used Rotella synthetic, which is 5w40. The engine started easily and ran just fine. Recently, I passed 100 hours and used Amsoil 15w40. I noticed right away that the engine seemed quieter. I wanted to use straight 30wt (synthetic), but the dealer didn't have.
I was taught (loooong ago) that diesel engines, which rev slower than most gas engines, are better off with heavier oil. This may not directly apply to the newer light truck engines (Powerstroke, etc.), but to me a tractor engine, which revs relatively slowly, could benefit from the better protection of a heavier oil /forums/images/graemlins/grin.gif

cp1969 · Jul 2, 2005

0w-30 is probably fine, especially if you are like me and end up changing the oil annually instead of at the hours limit. I'm running 10w-30 in mine because a.)that's what the manual, though outdated, says, and b.) I don't yet have a block heater and want the thinner oil so it will start in the winter. Since an oil change cycle for me encompasses both winter and summer, 10w-30 seems to fill the bill. If I install a block heater, I'll probably switch to 15w-40 because it is much easier to find.

gsxr1100 · Jul 2, 2005

depends on the adds and ZDDP in the oil. Also the pour pt, Noack Volatility, four ball, TBN, group #, etc etc.

cp1969 · Jul 2, 2005

( depends on the adds and ZDDP in the oil. Also the pour pt, Noack Volatility, four ball, TBN, group #, etc etc. )

Or, you could just look on the oil container and see if its API rating meets what is called out in the owner's manual. If so, you are, by definition, good to go. You can check out the oil ratings at api.org if you wonder if CI-4 oil is OK to use in lieu of CD (it is).

gsxr1100 · Jul 2, 2005

I agree 100% that if the ratings are good but some oils are better then others. Maybe a 0w-30 is great but without knowing some data on it, I do not know.

That would be like me saying any 15w-40 is good for all year long; which I can not state that. Then someone reads it way up north and thinks it is good to go when it is a dino oil and it not good to go for his app.

So case-in-point, a API rating just state it passes a certain spec. It does not know or care in what conditions it will see. An API rating to me, says what kind of auto it is good for. Now the area/region is up to the owner.