CAFE has Little to do with Motor Oil Viscosity Use

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Originally Posted By: spasm3
I ran my escape (20w spec'd) on 5w-30 and 0w30 till 155k, no problems, and no loss of fuel mileage. I have to believe its cafe. I am curious though why gm is still sticking with 30wts.



Cheap, proven and easy to find....
 
Hi,
Shannow - Yes you are correct about this Thread

As a matter of interest when I came to OZ around 1977 the "National Fleet" average for heavy trucks here was 5mpg! That is with 5 axle trucks at around 37metric tonnes and a speed limit of 50mph.

Today it is around >5.75mpg. This is a huge gain whilst the "stock viscosity" is still around 15W-40. Today this is obtained with 6 axle trucks and around 39 metric tonnes and a speed limit of 62mph

The gains come from a wide variety of sources - aerodynamics, radial tyres, better engine management systems and technologies, better roads etc.

In my own Fleet's case I could not reliably measure the gain in going from a 15W-40 mineral to a 5W-40 synthetic lubricant. Too many variables exist

Better fuel economy in any National Fleet will produce a real benefit to the Nation. Most personal vehicles idle lots and run on short trips - this is where lighter viscosities provide the most benefits to a Nation's Fleet average
 
Still think it is going to depend on the engines.

And when you think that turbos and DI are the future, the way oils hold up is going to have to be even better....
 
Originally Posted By: GMFan
We have a snow blower made in the 1960s that recommends 5w20 viscosity oil...says so on the sticker on the side of the oil pan.

Yeah and and it's a 99.9% that snow blower is operated below freezing temps... If that were the case for the same percentage of automotive applications, we'd be arguing 5W-20 was too thick and should be using a 0W-10 or similar...

Me, with the mfg'rs specking 30, 40W & thicker in high performance/stressed engines & in non CAFE environments, is proof enough for me that 5W-20 isn't necessary the mother's milk most think it is... Sure it's likely fine for 99% of the general public, it's that last 1% that doesn't think twice before running their engines to the max, that should be concerned with the viscosity...
 
Quote:
I don`t understand the easier starting thing. My car starts the exact same whether I`m using 20W50 or 5W30.



That may be ok for Texas, but up here where it can get to -30F and for vehicles speced for 30 weights, we use 0W30's or lower for winter use.
 
Originally Posted By: MolaKule
Quote:
I don`t understand the easier starting thing. My car starts the exact same whether I`m using 20W50 or 5W30.



That may be ok for Texas, but up here where it can get to -30F and for vehicles speced for 30 weights, we use 0W30's or lower for winter use.


True. Good luck starting the car in the winter on that stuff...
 
Originally Posted By: Capa
What's interesting is that engines last longer now, in the era of thin oils, than many decades back, in the era of thick oil.


In the era of thick oils(10-40) I used 5-20. Guess what? My engines purred like a kitten.
 
Originally Posted By: Doug Hillary
Most personal vehicles idle lots and run on short trips - this is where lighter viscosities provide the most benefits to a Nation's Fleet average


A lower viscosity here may improve mileage, but won't the viscosity be lowered severely (beyond the low starting value) as a result of fuel dilution.
 
Last edited:
Originally Posted By: AEHaas
From API.org, energy conserving oils is for the greater benefit seen on fleet vehicles, not for Your particular car:

Energy Conserving Designations
The bottom of the donut tells whether the oil has energy conserving properties when compared with a reference oil in an engine test.

Oils labeled as "Energy Conserving" have passed the test that measures an oil's ability to conserve energy. Widespread use of engine oils with this designation should result in an overall saving of fuel in the vehicle fleet as a whole, but a particular vehicle operator may not experience a fuel savings as a result of using these oils.

aehaas


I think that the benefit is for everyone, just not realized as much by the individual owner. Here the "benefit" is financial. As a whole it reduces the amount of oil required to be made into gas and easing of the effects of pollution on the environment.
 
Originally Posted By: vinu_neuro

A lower viscosity here may improve mileage, but won't the viscosity be lowered severely (beyond the low starting value) as a result of fuel dilution.


The proof is in the pudding. No, it won't. It'll be reduced a little bit, but certainly not "severely" and not out of grade. There is an entire forum section of UOA's, and I'll bet you can count on one hand the number of UOA's where a 20W oil has sheared out of grade. Secondly, if you're doing a lot of short trips, the oil spends most of its time being thicker than ideal anyway, so a slight amount of shear really isn't a big deal.

Oils are more shear-resistance, and fuel injection reduces the amount of fuel dumped in the oil, so in practical terms this just isn't an issue.
 
Originally Posted By: JOD
There is an entire forum section of UOA's, and I'll bet you can count on one hand the number of UOA's where a 20W oil has sheared out of grade.

Yeah but most 30w oils are in the lower 1/3 of their rated grade, while most 20W are in the upper 1/3, so the 20w will have to shear far more than the 30w to be out of grade... As I'm concerned, a oil with less than a 8 cSt is just plain scary & that's still in the upper 1/3 of the 20W grade...
 
Originally Posted By: JOD
Originally Posted By: vinu_neuro

A lower viscosity here may improve mileage, but won't the viscosity be lowered severely (beyond the low starting value) as a result of fuel dilution.


The proof is in the pudding. No, it won't. It'll be reduced a little bit, but certainly not "severely" and not out of grade. There is an entire forum section of UOA's, and I'll bet you can count on one hand the number of UOA's where a 20W oil has sheared out of grade. Secondly, if you're doing a lot of short trips, the oil spends most of its time being thicker than ideal anyway, so a slight amount of shear really isn't a big deal.

Oils are more shear-resistance, and fuel injection reduces the amount of fuel dumped in the oil, so in practical terms this just isn't an issue.


Shear resistance is fine in most oils. Fuel dilution is a different issue and a serious one in short-trip use.
 
Originally Posted By: TFB1
Originally Posted By: JOD
There is an entire forum section of UOA's, and I'll bet you can count on one hand the number of UOA's where a 20W oil has sheared out of grade.

Yeah but most 30w oils are in the lower 1/3 of their rated grade, while most 20W are in the upper 1/3, so the 20w will have to shear far more than the 30w to be out of grade... As I'm concerned, a oil with less than a 8 cSt is just plain scary & that's still in the upper 1/3 of the 20W grade...

Install an oil pressure gauge and you'll learn first hand just how "unscary" running a 7cSt oil is in a 20wt application and even a 30wt app'. It's more difficult than you realize to actually run an oil that is "too light".
 
Originally Posted By: vinu_neuro
Originally Posted By: JOD
Originally Posted By: vinu_neuro

A lower viscosity here may improve mileage, but won't the viscosity be lowered severely (beyond the low starting value) as a result of fuel dilution.


The proof is in the pudding. No, it won't. It'll be reduced a little bit, but certainly not "severely" and not out of grade. There is an entire forum section of UOA's, and I'll bet you can count on one hand the number of UOA's where a 20W oil has sheared out of grade. Secondly, if you're doing a lot of short trips, the oil spends most of its time being thicker than ideal anyway, so a slight amount of shear really isn't a big deal.

Oils are more shear-resistance, and fuel injection reduces the amount of fuel dumped in the oil, so in practical terms this just isn't an issue.


Shear resistance is fine in most oils. Fuel dilution is a different issue and a serious one in short-trip use.

Short trips, particularly in a winter is hard on engines and shortens the life of motor oil for a number of reasons including the possibility of fuel dilution. But since the oil is not getting up to temperature even a diluted 20wt oil is still thicker than necessary under such operating conditions.
 
Originally Posted By: CATERHAM

Short trips, particularly in a winter is hard on engines and shortens the life of motor oil for a number of reasons including the possibility of fuel dilution. But since the oil is not getting up to temperature even a diluted 20wt oil is still thicker than necessary under such operating conditions.


I don't agree with your oil pressure driven basis of selecting oils, but this is a good point.
 
An OP gauge is an effective viscometer.
It is unfortunate that most vehicles no longer come equipped with them. But even if they did most owners wouldn't (and don't) understand how to use them.
 
Originally Posted By: CATERHAM
An OP gauge is an effective viscometer.
It is unfortunate that most vehicles no longer come equipped with them. But even if they did most owners wouldn't (and don't) understand how to use them.


The only areas that are oil pressure dependent are crank bearings and journals and cam journals. However these are low wear areas because they're hydrodynamically lubricated.

Cams/rockers and more importantly rings/bores, the high wear areas in almost all engines, are splash lubricated. These are not oil pressure dependent.
 
Bearings aren't pressure dependent, the pressure only ensures that adequate volumes get there. Under some circumstances, the bearings can provide significant suction to the oil supply.

CATERHAM has correlated the rate at which the bearing passes oil through it with the HTHS, and found that gallery pressure relates well to it.
 
In my case, 30w gives me an increase of 2mpg on the average over 10w/30. This is due to oil consumption lowering my octane on thinner oils. I shudder to think what 5w/20 would do to my particular car.
My best mpg's are with 10w/40 and straight 30w's. Once the "energy conserving oils" shear down, consumption goes way up and mpg's go down.
May not be useful info in the modern world, but it is what it is.
 
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