Originally Posted By: autoreign
Originally Posted By: OVERK1LL
I still say it is application and power density specific, even on engines with identical clearances.
Look at Ford's Modular engines for example. The "Civilian" versions call for 5w20, whilst the Supercharged Ford GT and Shelby GT500 both spec 5w50. They have the same clearances as their non-supercharged siblings.
Power/Load is a factor in bearing design as you correctly put (later part). Power goes up, Viscosity goes up. No issue here.
I am aware I put it correctly. That is why I stated it....
Quote:
Originally Posted By: OVERK1LL
Ford of Australia specs 5w30 to 20w50 for the same engines that spec 5w20 here.
Thicker oil never a issue as far as reliability is concern. Just less efficient. Not sure if Australian's bearing specification is the same as that of US version. If so, it is a case of specifying for higher safety factor.
1. They are the same.
2. Why the higher safety margin if 5w20 is "just fine".
3. Considering #1 & #2, what role do you feel CAFE has in this?
Note that I am not saying that 5w20 is NOT adequate; given the amassment of 4.6L Modular engines racking up ridiculous mileage, it is obvious that it IS. My point is simply that a lighter oil is only adequate when power density, engine design, lubrication system design and COOLING are considered in concert.
One cannot run a thin oil in an engine with a high specific power output without adequate oil cooling. As obviously, temperature plays a key role in the oil's snapshot viscosity.
Quote:
Originally Posted By: OVERK1LL
In regards to clearances on newer engines being tighter:
Back in the day, engines were often hand assembled. Pistons were hand-fitted to the bores, balanced, rods were numbered....etc. On a 302 we tore down the year before last, FACTORY 1990 HO engine. The pistons were ground underneath due to the balancing performed, the rods were ALL numbered....etc.
Fast forward to GM's LSx engines, the bores are all done "bulk", with pistons from a bin of pre-sized pistons fitted to the bores. The variance in piston-to-bore clearance is what perpetuated the biggest issue with the LSx engines: Their propensity to piston-slap! This wouldn't have been an issue with hand-fitted pistons in measured bores.
So while manufacturing equipment has improved over the years, and process has been refined, there is still something to be said for hand built vs bulk assembly as to consistency of clearances and adherence to tolerances.
What is your point here WRT to this topic? Older road vehicles have tighter clearance? If that is the case, it is a situation of design with higher safety factor perhaps to cater for human error as it is expected. Each individual has different level of skill.
BTW, specific balancing needs to have all parts numbered to correctly identify which part goes where.
1. My initial point was that a series of engines that are hand assembled have a likelihood to remain consistently close to a mean tolerance level in regards to assembly. I made no mention of clearances. Really, if you look back, they really haven't changed a whole lot over the years. There were no changes in clearances OR tolerances in Ford's Modular engines when the switch from 5w30 to 5w20 occurred.
2. Humans measuring components are a known quantity. Yes, there are expected variances. But certainly, there are LESS variances, or rather, the variance from a given mean is far less than with engine blocks that are bulk-bored and stuffed with components out of the bulk bin with the deviation from a given spec lying solely in the hands of the manufacturer of that specific part.
Again, I can bring up the piston-slap issue with the LSx engines as an example here. This was NOT an issue with hand-fitted piston engines.
3. The very reason I mentioned the numbering of parts was in reference to the balancing process. I've been around engines my entire life, I'm far from "new". Most of my early experience came from the boat-side of things, but that is really irrelevant.
4. I really feel like you are talking to me like I am an idiot and this is all some sort of lesson that you are taking me by the hand through......Guiding me along. Whilst explaining points to me I made based on my understanding of those points to begin with. If this is not your intention, I apologize, but I have to say, that is how this is coming across.
Quote:
Originally Posted By: OVERK1LL
Another note "for the record books" that has been discussed on here is that many older 5w30 oils sheered down to a 20-weight quite readily. Essentially meaning, that for the last 30 years, people running 5w30 were, in short order, running 5w30 anyways. And these are the same "loose clearance" engines SteveSRT8 was talking about.
Wt30 oil
shear down to wt20 is expected through time. Wt20 shear down to what...?
They don't. Or at least not to any meaningful degree.
Oils are now vastly more sheer stable than they were even 10 years ago. A quick look through the UOA section on this site makes that readily apparent.
That is why I brought up the point about 20 weight oils not being "new". They really aren't.
I'm not really sure where the push to run 20w50 in everything came from, it certainly was not the manufactures.
Quote:
Originally Posted By: OVERK1LL
Not to mention the plethora of marine engines we had at our cottage that spec'd anything from a 20 weight to a 40 weight depending on manufacturer and dated back to the 1920's through to the 1950's.
Marine engines <> Road vehicle engines. Specification is totally different therefore not comparable.
Really? So our Ford Y-block engines, of which we had a few, were not the same as their automotive counterparts?
They were identical.
As were the Ford flathead engines we used.
Chrysler made a number of marine-specific engines, for example a version of the 318 called the "Fury 190", as well as a 300HP version of the 440, of which we've owned two. Both were VERY similar to their automotive counterparts, other than the difference in camshaft choice and the fitment of marine manifolds.
There WERE some very marine-specific engines, such as those produced by Gray, but you would be surprised at the number of engines that were nothing more than a variant of their automotive counterpart with a flame arrester and some water cooled manifolds fitted to them.
Quote:
Originally Posted By: OVERK1LL
I think the biggest determining factor is power density: Engines with higher power output require heavier oil to protect them when somebody is pushing the envelope.
One needs to simply look at the Ford GT, GT 500, Chrysler's SRT engines, BMW's M-engines...etc to see that there is a common theme with a heavier viscosity being specified than their more "mediocre" siblings.
Assuming that all design factors remain the same. Viscosity is a function directly affected by Power/Load as you correctly put.
Also take note that viscosity is a function directly affected by the square of clearance. Which is a more important factor? Power or clearance? (Refer to sommerfeld chart if you need to learn about this).
Looked it up, quite fascinating. I didn't take Mech. Eng, so I've bookmarked some info on it for further reading.
What I'm seeing with the above which you (probably intentionally to bug me
) omitted is of course the control of oil temperature, which I mentioned earlier. This also has a direct bearing on viscosity, as bearing design specifically includes the temperature of the oil as this is the key factor in the lubricant's operating viscosity. Temperature control: measured inlet and outlet temperature and providing adequate cooling to keep the oil within the calculated acceptable range, as well as a buffer for cold starts and snap-loads need to be factored in as well.
Another point we didn't discuss was bearing support structure, or bottom-end rigidity.
This has been something that ALL manufacturers have improved upon immensely and plays a major role in the ability to run thinner oils, reliably, and in conjunction with lubricant cooling, allow for much greater long-term durability.
If one compares the bottom-end structure of a Ford Windsor engine to that of a Modular, or even LSx engine, there is no comparison. The latter feature deep skirts with multi-bolt main caps with side-bolts and a generally beefier block structure.
This is key in providing a rigid framework for the bearings and crankshaft and to prevent flex and walk. With a more rigid bottom-end, you eliminate a lot of the unwanted crankshaft movement that, in older engines, at the same power level, could breach the hydrodynamic wedge through a walk or flex event and cause bearing damage.
Quote:
Originally Posted By: OVERK1LL
I also don't think that one example of an engine built for the purpose of putting down numbers on a dyno should be viewed as a "see, this is why" example, when it is VERY clear that if it was that cut and dry, then the cars I mentioned above would not be running heavier oils. An OEM has to consider all the bases and potential usage scenarios that could potentially cause warranty issues and cost them money.
Agree with you. However, it does not mean that clearance is not a factor affecting viscosity. That is mine point.
I agree. I'm not saying it isn't a factor either. Only that it is not the ONLY factor, and that there is much more contributing to engines running reliably on thinner oils in applications engineered for them. All the while allowing for the fact that there will be variances in the specified viscosity within an engine family depending upon the specific output of the engine in question, especially when fitted with forced-induction.
And even then, one must also acknowledge that CAFE does play a role. Again using Ford as an example, specifying two different weights for the same engine in two different countries this casts an odd shadow on the idea some have that you MUST run the viscosity on the fill cap or risk damaging the engine.
As you mentioned, and I agree, going up in viscosity is normally not an issue for anything other than efficiency.
