cmdln

I still don't understand why you would want to run a higher weight.
The kinimatic viscosity or flow measured in centistrokes (1 Centistoke (cSt) = 1 mm2 /s) of 30 weight oil has a minimum of 9.3 cSt and a maximum of <12.5 cSt at 100°C. A 40 weight oil has a minimum of 12.5 cSt and a maximum of <16.3 at cSt at 100°C.

So at operating temp the 40 weight oil is thicker and therefor has less flow and less lubrication (assuming you can maintain proper oil pressure to maintain proper circulation).
So I am still trying to figure out why someone would want to run a higher weight oil. Can someone link me to some information that illustrates the reason (minus having high clearances in your engine and needing higher weight to maintain proper pressure and circulation).

TexanTaco

cmdln, I think part of it (especially when looking at M1 specifically) is that 30 weight (operating temp) synthetic oil tends to be on the "thin" side compared to conventional dino oil. So running 40w is nothing if you are using a true synthetic, which M1 may or may not be anyway. I would also think that a thicker oil would tend to shear less and break down more slowly, but I'm not 100% sure about that.

Thanks ARB for the info about no 0w dino oils. I guess it's impossible to create a 0 weight start up with thicker dino.

mkgarrison5

with out UOA's its speculation. you can type every scientific formula you can think of but without proof on how your motor reacts to any oil its all speculation.. who knows a 5w20 might be the best for the 3.4's.. not likely but you dont know without actual backup to prove it....also a low 40w might be the best. you just dont know. i have read many many uoa's and lot of folks run the 0w40 esp in VW's, Audis, jeeps and vehicles with a lot of miles and they come out with really good uoa's...i know the yota motors are very different than the above. but since its a synthetic weight it will flow much better than the dino counterparts.. i would run an 0w40 with out thinking twice about it esp in the summer.

cmdln

Well I found thischart. According to it at least specification wise 0w40 has the same shear guidelines a 30 weight oil. 2.9 mPa-s at 150°C Min.

Now I know thats just the guidelines and actual shear rate may differ. So does someone have shear rate numbers for different oil formulations that specifically compare 30 to 40 instead of brand x to y? Amsoil may have better shear protection than Mobile1 but I dont think that has anything to do with 30 to 40 formulations. I would just want to see some numbers before running thicker oil.
The shear rate is how well it holds its viscosity at high temps right? So its still a matter of how well the oil holds up and you were talking about doing OCI of 5K. So say the shear rate of the oil is the same. 40 wont drop under the spec for 30 as fast as 30 will drop under spec. But it seems like your just exposing your engine to less lubricity until the 40 oil starts to degrade and come into spec as a 30 viscosity.

Im not saying I have any answers I just get tired of people saying Ive run it for a long time with no issue. Well for years people ran regular oil with no issues. It seems the point of these oil conversations is to determine what is best for the engine and just coping out and saying running 40 is ok because its a thin 40 does not answer any questions. All oil shears and it seems like thats the only cited reason to run a higher weight, because it will holdup against shear better. But no one has any data to support that.

mkgarrison5

in theory if you run a light 40weight you can literally run that till it shears to a 30 weight.. granted i wouldnt wait that long but some do... i was just giving him an option. in the texas heat it will not be an issue at all if he wants to run 0w40... now if the 30weight shears to a 20 weight then you may start getting some issues with bad wear and etc.. if i were to run a 0w40 for myself ( 85% highway and 15% city) i would run it 8-10k miles esp if it was a good syn like amsoil, PP, Schaeffers... bc if it shears to a high 30 weight then woopty do. no big deal... as i said for him its his choice. he is fine with a 5w30. but he can run a 0w40 if it makes him feel better... btw make sure you charts are for synthetics not dino.. btw the 30 weight syns are on the thin side of the spectrum so bumping up is deff no issue at all. btw go to bitog you may find some very interesting info.. shearing is only a portion of it.. running a higher weight may reduce wear #'s across the board but again no UOA's = speculation

TexanTaco

There is a lot of great advice here and on BITOG, but some of the stuff there just goes over my head. Like ARB said you should always be in good shape if you just change the oil when you are supposed. Now finding out exactly when you should change can be tricky, and without UOA's you are kind of guessing. But the basic guidelines are there, like 3k intervals for dino and 6k for synthetic.

mkgarrison, I can't tell my wife I'm getting advice from a Tarheel. She is a Duke grad. It's funny though, I loved watching UNC basketball when I was younger. But now I'm not allowed to even remotely like them.

cmdln

I just enjoyed beating Roy this year

cmdln <-- from lawrence ks

TexanTaco

Kansas was awesome last season, I couldn't believe how quickly they took over that game. UNC did catch up but it wasn't nearly enough.

And concerning Duke, I think Coach K's best chance to win will be with Team USA.