Ok, point taken. Now I will ask only 1 question. What temperature do the internal parts reach that the oil comes in contact with (examples: piston, wrist pin and valves just to name a few). Stands to reason that the oil can see extreme temps. I'm gonna go out on a limb here and say that just maybe that is why there is such a thing as an oil cooler to begin with. The oil not only lubricates an engine, it also pulls with it some heat from internal parts.
That is true; localized temps do get above the sump temps. A great example would be turbos; they get extremely hot as the EGTs saturate the components of the turbo. The concept I'll cover below would apply to any component we'd discuss here; turbos, piston rings, etc
However, we're now going to get into the concept of thermal energy transfer ...
While an engine is running, those turbos are nearly always cooled by either lube oil and/or engine coolant. We'll just focus on the lube cooling effects here and just realize that the coolant (if present in the turbo design) will be similar, but not always identical.
Thermal energy transfer relies on many things to achieve it's tasks. Without getting deep into thermodynamic theory and mathematics, we'll just agree that the transfer rate is controlled by several things:
- rate of fluid flow
- total volume of fluid moved
- temps of the saturation pick-up point (turbo, et al.)
- temps of the rejection dump point (oil cooler or radiator)
- ambient temps
- etc
When oil is moving through a turbo, the EGTs may be around 1300-1600F for a diesel, or up closer to 2000F for a gas engine. That's HOT !!! Those temps are WELL above the sustainable temps that any typical lube could ever endure. And yet, they don't coke in the first 30 seconds of use. Why not? Because of the thermal transfer rates relative to the criteria listed above. When the oil is moving over the surface of the components (bearings, shafts, etc), it's not only lubricating and cleaning, but also cooling because it picks up heat energy and carries it away to the disposal point. But each mL of fluid does not take ALL the heat ALL at once. It only carries a small portion of that energy, and is replaced by the next mL behind it. Each mL does not have to carry off 1400F individually, but the total volume of fluid moved will carry away enough such that the desired effect (a cooled turbo) is satisfied while not overheating the lube. This is a matter of volumetric exchange versus energy being absorbed/rejected.
The most easy way I can help folks understand this is to do a very simple home experiment. Go get a candle and some matches. Light the candle and set it on the counter table and light it. Now do three separate experiments, one after the other:
- first, spread your fingers widely apart, and quickly pass your fingers over the flame, one finger at a time, only 2" above the tip of the flame
- next, close your fingers together, and slowly pass your fingers over the flame tip
- last, cup your palm/fingers and hold the hand still over the flame as long as you dare
In the first stage of the experiment, you'll feel very little if any sensible heat in your fingers because your fingers were exposed for a very short time. But, your fingers most certainly did absorb heat, it just didn't get "hot" enough for your fingers to feel it. A little heat went into your fingers and the rest escaped around them. But if you had enough hands and fingers, all moving along together, you could absorb a lot of energy, yet none would burn.
In the second stage of the experiment, you'll feel heat for sure, but you may not "burn" your fingers. The amount of energy your fingers absorbed for that single pass increased substantially, but not to a point of destroying flesh. The longer exposure relative to the heat present causes more to got into each individual finger. In the last stage, well, it's obvious what's going to happen; you'll suffer a third degree burn if you leave it there long enough; very undesirable.
Engine oil cools in the same concept. Any one mL of lube does not have to cool the entire heat load; it only has to carry away a portion of that load. When an engine's lube system is designed well, there's plenty of volumetric flow of the lube, plenty of absorsion surface area, and enough rejection potential that all balances well and the oil's localized temps do not exceed the capability of the lube.
It's completely true to say that premium syns (group IV and V) are more capable of sustaining higher temps for longer periods of time, versus a typical group II or II+. Group III probably falls somewhere in between.
The overall effect of thermal energy transfer depends on a host of things I enumerated above. In a well designed lube system, the thermal energy effects are taken into account for the expected application operational conditions. If the system is not well designed, it's not going to end well for the lube or the engine. OTR truck engines are designed for their expected heavy loads. Race cars have larger coolers and syns because they experience loads higher than typical street cars, AND because weight means drag, they want the smallest system which can sustain the load, so syns help here.
It's not that any dino oil can't do the same heat-load transfer that a syn could do, but it might needs X.X more mL of fluid per second to achieve the same task. And, as I stated, that's a part of the design team's job to make sure the conditions for the thermal transfer are satisfied. Most of us know that cars like the Corvette, Porches and others come with syns right from the factory. Is that lube "needed" or just a precautionary effect? Well, that depends upon a few things.
- That brand new 'Vette which is driven by a 71 year old tooling around the fall-season country roads while looking at the leaves change color, driving at the posted speed limit, really isn't taxing the engine or cooling system. Having a syn in the engine is unneeded; a dino would do this job very well.
- But that same 'Vetter when given to his 35 year old son who club races it on the weekends might well need the extra capacity of the syns, simply because he may be maxing out the available cooling capacity when it's 93F ambient and he's hitting redline near every corner entrance.
This goes back to my point in my previous post. These are all a matter of knowing what the capabilities of the components, systems and products are. Any lube (of any base stock), can either be under-utilized, or overwhelmed, simply by not having the right combination of systems and products in place.
- if you place products in a condition where their operational experience is well within the design intent, then it's improbable you'll ever discern any differences between the differences in product capability, because by definition they're not pushed past the limit of the lessor capable product; it really doesn't matter what you use
- as you increase the conditional extremes, it's likely that one product will exceed the capability of the lessor; you'll need to be more critical in your product selection
- when you raise the conditional stresses high enough, it's likely that any product will fail, and you need to redesign your system overall
Some engines don't have the best designs. I can think of one example off the top of my head; the old SL2 Saturn engines. They had rings with no drain-back path; this was a design choice to increase the sealing effect for combustion efficiency desired. However, the long term maintenance effect was that oil would coke on the rings, and ultimately harm the very sealing effect they were after; a terrible design if you ask me. Syns might last a little longer in an OCI versus a conventional lube, but the reality is that it was a poor design and syns only delayed the undesired effect, they didn't stop the effect. Some engines like the old 6.0L PSD had oil coolers which were OK when new, but then clogged (coolant side) and reduced the thermal transfer rate such that the oil cooling was severely degraded, and that compromised the lube. As it degraded, it's true that a syn lube might have delayed some of the ill effects by taking a bit more heat load relative to the rejection rate, but eventually the condition would be bad enough that even a syn wasn't going to overcome the inevitable.
Conversely, an engine like the GM 6.6L Dmax has an oil system that seems to be so well designed that it really doesn't matter what lube is used, because the oil temps never seem to get extreme under any OEM operational conditions.
Or, consider the effect of "cool down" timers in vehicle with turbos. Whether you do it manually by letting the engine idle a bit before shutdown, or (as I understand it now) some gas turbo cars now have separate cooling loops (coolant, not oil) which are on separate electrically driven pumps which actually can continue to cycle the coolant after the engine is shut off, such that the turbo is cooled to a safe level regardless of how/when the engine is shut down. A design team took the load and transfer goals and then met them with an alternative method that does not rely on manual driver intervention. But if you flog your engine in a merciless manner, and then shut the engine down while badly heat saturated, you might be able to coke any lube in the turbo, regardless of the oil's base stock.
So, YES, I agree with you. And NO, it does not always matter. What matters is how the entire system is designed and what products you select, relative to your operational conditions.
Under normal OCIs, no extreme temps, normal operational loads, etc. It is highly improbable that a syn would do anything "better" given those constraints.
