My guess is that whether a 5w-20 works as well as a 5w-30 is engine specific. Ford & Honda certified only certain, recent engines for the thinner weight. It would be interesting to compare 5w-20 vs. 5w-30 across those engines.
It could turnout much different than we expect.
Look at it this way: 5W20 has lower viscosity spread, which mean fewer VII's to shear back
so expect less sludging, but does it have the film strength to prevent wear?
I still beleive this is mostly for CAFE purposes.
As for me, I will stick with the narrow vis. spread 10W30, the workhorse of the industry. Just the right film thickness for the most economy.
If you guys check out the oil analysis document on Maxima.org, there are a few new Fords and Hondas on there that did oil analysis at first with their 5w20 oils. I see they have a lot of moly in the analysis, but I don't know if it comes specifically in the 5w20 oil, or if the factory added some sort of break in additive. It would be interesting to see a virgin sample of 5w20 oil from Ford and Honda's dealerships, and see if indeed they contain moly. Perhaps this is why 5w20 oil is so expensive? This oil is a mystery to me, I hear that they can't make this 5w20 oil unless it's got a stronger base oil than typical dinos. But why? With less of a viscosity spread I figure this oil should be easy to make, no? So why is it so costly? Or is it just expensive because the oil companies know that people will pay the elevated price to get this rare oil, since it's not a common viscosity yet?
If they are adding moly to the 5w20 oils out there, that would mean they aren't confident that this viscosity can protect well enough on it's own, and it must have the moly to avoid severe engine wear. That's another one of my theories.
I expect that you are right on the CAFE issue, for Ford anyway. But Honda has always been greenest of the car companies, so I suspect that they may have more altruistic motives.
Good point about shear. Combine that with Terry's observation (on another board, perhaps here also) that many 5w-30s shear to 5w-20 in use, and 5w-20 does not seem so odd. It's at least as good as earlier 5w-30s, without the sludgy sheared VI improvers.
"This oil is a mystery to me, I hear that they can't make this 5w20 oil unless it's got a
stronger base oil than typical dinos. But why? "
We know that lower viscosity oils tend to volatize (evaporate) quicker than the thicker oils. Since the newer oil specs are becoming more severe with respect to viscosity change, volatility, and oil life, the base oil has to be more robust. Now, the only base oils I see being able to take the punch, is a Group II+ or III with the addition of PAO and/or esters for economic reasons. [I am qualifying this wrt OTC oils only.] Since the lower vis. oils tend to have thinner films, one would have to have a good load of fm's, either in the form of organometallics or esters.
Personal Opinion: I for one would not run a pure dino oil in 5W20 unless I knew it had some good fm's.
Oil: do we really know what works anymore? Ford & Honda are pushing 5w-20. Terry wants a 5w-60. Johnny loves those Euro 0w-40s. Bob wants oil to plate out on his tests.
And so forth.
Most interesting to me, the tech article explaining that the Euro penchant for higher vis oil is likely because they have to lubricate HOT engines working hard buzzing down the autobahn for hours at speeds not legally seen most anywhere else.
We talk about everything but film strength as a function of operating temperature.
That is, maybe, given modern engines, with more than ample cooling systems, and group 2 or better base stocks plus a good additive package, thinner lubes work just fine. Running around town or running on the highway, engine conditions just don’t get hot enough to compromise the film strength of, say, a 5w-20.
And if Honda & Ford are right, you save a little gas and pollute a little less.
I'm dying to see some oil analysis tests on the new 5w20 oils, especially if that same car has tests on 5w30 or 10w30 oils too, to compare wear numbers. My gut feeling tells me the 5w20 will show worse numbers.
I've been thinking about this and I'm a bit confused. You say the thinner oils tend to volatize quicker, but wouldn't that also mean that the 5w30 oils out there would need to be using the stronger base stock just the same as 5w20 since they both start out as 5 weights? Wouldn't a 5w30 and 5w20 oil be very similar other than the fact that the 5w20 needs less VI improvers? Or do the 5w30s now all have a base stock identical to the 5w20s?
Sounds like you and I have been thinking about the same thing Patman.
What does a viscosity improver have to do with film strength? Does the use of VI improvers help film strength? I know that 5Wx oils shear back to 5W under extreme stress so wouldn't the film strength of all 5Wx oils(in general and within each class) end up the same. If this is the case, then would'nt the lightest oil that maintains proper oil pressure be the one to go with?
This is more in the line of a question than a statement. I'm not sure about the mechanics of this.
I was referring to future oils that would have to meet GF-4 and GF4+.
Some VI's (multifunctional fluids) do act as Friction Modifiers as well.
The current base stocks are most likely the same for 5W20 and 5W30's, just different levels of VII's.
Also..........be aware that a 5W20 does not always have to start out as a 5W, it depends an the Viscosity Index of the base stock does it not?
The straight-weight 30 (synthetic) that I am currently experimenting with has a Viscosity Index
that is almost as high as some petroleum 10W30's and a pour point that is the same as some petro 10W30's. Now, if they wanted to make it a real 10W30, how much VI improvers would they need to add?
So, a 5W20 could actually be a 10 or even a 15 weight base stock with a high enough Viscosity Index to not neccessitate the need for a whack of VI improvers.
[ July 12, 2002, 08:47 PM: Message edited by: GW ]
"So, a 5W20 could actually be a 10 or even a 15 weight base stock with a high enough Viscosity Index to not neccessitate the need for a whack of VI improvers."
I would think that to be true of full synth's but not of dino's. Synth's start out with a low vis for their PAO's and add the higher vis. esters, which results in an overall higher vis base to start with.