Quote:
... which of these oils has better overall attributes? Specifically, better performance in cold weather (i.e. cold starts in less than 30F weather) and (in theory) better performance in high heat (110F)?
Ok, I guess I made a jump from theory to reality. You see, I interpreted the quote above from your question in that you presume that "attributes" (VOA data) translates directly into "performance" (real world wear control). I have yet to see any proof that establishes that the differences in VOA info translate into significant differences in wear control for decent quality certified lubes applied to the spec in which they are intended.
You've got two entirely separate topics jammed into one question.
If you want to discuss "attributes" in the bottle, fine.
If you want to discuss "performance" in your crankcase, fine.
If you want to assume that the former has a direct, proven link to the later, you're mistaken.
Now, I do see that you want to define the cold performance at less than 30F. Frankly, that is a useless magnitude to concern yourself with. Had you asked about those products at -30F, you might see some difference. But not at +30F. Therefore, the VOA data has no real value at that point. Those three lubes, as well as many others, are going to pump just fine in your engine. I'm not going to concern myself with an old, IDI farm tractor here; you're driving a modern common rail injected diesel that has great engineering and design characteristics. There is no reason to think that a dino 15w-40 is going to be worse (the opposite of better) than a 5w-40 at 10F or 20F, in terms of being able to "start" the engine. It will start just fine with either. And in terms of wear control, there's just such a tiny, infinitesimal difference (if it even exists at all) that you'll NEVER see the "performance" manifest into some tangible issue in wear rates. If your OP had asked about those attributes at -30F, it might matter. But you don't get anywhere that cold where you're at, so it's moot to your application. I do agree that it may make some difference at uber bold temps (below -30F), but that wasn't your question now, was it? You asked about below 30F, and any of those will do just fine; there is no realistic belief that those lubes will give a "better" cold start, one versus the other.
Similarly, you're asking about 110F. But your engine does not operate there at that temp; it's a pass-through point on the way to around 200F-215F. "Normal" operating temps are much higher than your arbitrary 110F. All lubes are going to do just about the same in both those conditions; 30F and 110F are just ambient temps where the lubes will respond in some temporary manner. And that "performance" you're concerned with is just fleeting. You're presuming that the exterior ambient temp really means something to wear control and frankly it doesn't. While NOACK data can show which engine lube might has resistance to evaporation and consumption, those two characteristics have not shown any link whatsoever to wear control. I.E. you might have to top off a lube more often due to a poorer (higher) NOACK number, but that does not mean it won't control wear just the same. Whether it is 65F outside or 105F outside, the engine lube is not going to do better or worse in terms of wear control. That ambient temp will only affect the cooling system in terms of it's rate of ability to reject heat into the atmosphere. Until you're at the engineering limit of your cooling system, heat transfer rates are moot; they do what they are supposed to do. 65F isn't going to affect wear rates of your engine any less than 110F. The theromstat in your cooling system is going to manage the temps in the engine to be around 210F or so. So why are you asking about ambient temps when they only affect cooling rates, not wear rates??? I do understand that oil is used as a cooling medium in the engine, but that oil temp is controlled by a far larger, more elaborate liquid "coolant" system. The "coolant" directly cools it's internal liquid, which in term cools the engine via direct contact at the surfaces as well as indirectly via the oil. That oil is kept around 210"ish" on purpose; it's the designed op temp. The ambient temp only affects the rate of thermal energy transfer of the main coolant system; it does not affect wear in any real sense. If the coolant system needs to reject more or less heat, it will use the thermostats (two loops in your engine) to manage the temp to it's desired level. As long as the cooling system is not maxed out and put into a condition past it's capacity, then it will keep ANY lube at the prescribed temp. Therefore the ambient temp will not alter the engine temp much, at least not past a point of danger. I've seen no data to prove that NOACK scores have a direct linear link to wear rates. So ambient temps don't really matter in that regard. Ambient temps affect cooling rates, not wear rates.
Simply put, you cannot presume that the VOA data you're reviewing makes any difference in your crankcase in your application given the parameters you've laid out. Any of those three will do just fine probably down to perhaps -10F or even less, because they will all "cold start" equally well in your modern engine. And in terms of hot weather, the ambient temp does not greatly affect the NOACK score because that is presumed to be important at operating temps controlled by the cooling system, not ambient temps controlled by mother nature.
