Originally Posted by Dak27
Originally Posted by dnewton3
OP -But as for results, there's rarely any distinction between the two. Wear data will not show any significant difference in just about any application.
Judging by the UOAs I've had ran on Delvac Super 1300 and Delo 400 SDE 15W40 and Delo 400 XLE and Delvac Elite 10W30, you're 100% correct when it comes to my Detroit Series 60.
I personally use 10W30 in the winter and 15W40 for the rest of the year. My motor definitely turns over easier in the winter using 10W30.
I believe Tired Trucker runs 10W30 year round in his Detroit, and he's stated the 10W30 shears less in his motor. Dusty uses 10W30 year round also, and as you've already stated, his UOA looked impressive to say the least.
I've noticed slightly lower oil temperatures using 15W40 in the hotter months. Not a huge difference compared to 10W30, but enough that I'd rather use the 15W40 when the ambient temperatures get past 85F. To steal a line Tired Trucker, it helps my paranoia gland when my oil temperature is lower.
Nothing wrong with using a 15w-40 in summer. But as you can already see, whereas using the 15w-40 will reduce temps, it does not necessarily reduce wear.
The point? There's no correlation between wear and the moderate temp shift. Admittedly large temp shifts would be something to concern yourself with, but I seriously doubt that's what we're talking about here.
And out of curiosity, are you speaking of the oil temp, or overall engine temp?
Large grade shifts can certainly be a cause for concern as they might induce a wear shift. Much of this is situation dependent.
Going from a 5w-20 to a 20w-50 in winter in your gasser might be a problem for both starting and wear.
Going to a 5w-20 where a 10w-40 is spec'd in low-pressure (low boundary film layer) application might also be an issue.
- There are examples such as the Ford 4.6L and 5.4L engines running anything from 5w-20 to 10w-40, and they seem immune to wear changes.
- Other examples can be seen; some extreme grade changes induce wear; there's a UOA here from a Dmax diesel that used 15w-40, plus adding Lucas oil stabilizer, and then a non-standard oil filter with no bypass relief; this combination of super thick oil and odd filter has driven up the Al in wear metals.
- Other Dmax examples have shown that in "normal" choice selections, the difference between 15w-40 and 10w-30 are totally moot.
My point is that there are times when grade will matter, and other times it won't. If you cause a LARGE variation in grade, it might affect wear. But generally, going up or down only one grade amounts to no change in wear rates whatsoever. Using a 5w instead of 10w? Not really going to make much difference. Using a 30 grade instead of 40 grade, or 30 grade instead of 20 grade? Moving up or down one grade really doesn't make a hoot of difference in wear control.
The real exception to this is in your cold start capabilities. If you're right on the feathery edge of being able to crank over, then dropping a grade will help out quite a bit. But we're talking about -20F and lower; not "gosh .... it's going to drop down to 43F tomorrow morning, I'd better start using my 0w-20 PAO or my engine will lock up ...."
A grade shift up/down just one category generally has shown no statistical significance in wear control in more than 15,000 UOAs I've looked at.
If the grade shift induces a temp shift, and that temp you're concerned about is on the feathery edge of acceptable, then that might be the reason to use a different grade. Say you were within a few degrees of the temp causing a cooling fan to engage, then choosing the lube that reduces temps would have the effect of improving fuel economy, because when the fan does not come on, or would come on less often (regardless if it's directly or indirectly driven fan), then the net result is less fuel consumed to provide the power to that fan above the power required to move the vehicle. But if the temps are well in control, again, it does not make a difference because it would not change the general operation of the temp controlled condition.