Obvious to many here - but worth repeating

[Vaca]

The SAE weights - 20, 30, 40, 50, etc - are not proportional to the actual viscosity they are are indicating. For instance, a typical 20 weight oil does not have half the viscosity of a typical 40 weight oil.

Looking at the numbers for two commonly used (and discussed here on BITOG) oils we find Mobil 1 Advanced Fuel Economy 0w20 has a 100C viscosity of 8.7 which is two-thirds as thick as the 12.9 of Mobil 1 0w-40 FS.

Looking at the HTHS measurement we find the difference between these two oils is even narrower, 2.7 of the 0w-20 is three-quarters as thick as the 3.6 of the 0w-40.

While obviously there is a difference between these two oils; the difference may not be as large as some of the thick/thin arguers make it out to be.

 

[Quattro Pete]

Originally Posted By: Vaca
The SAE weights - 20, 30, 40, 50, etc - are not proportional to the actual viscosity they are are indicating. For instance, a typical 20 weight oil does not have half the viscosity of a typical 40 weight oil.
Another thing worth reminding is that it's not a "weight". It's a grade. And it's a grade that represents a whole range of possible viscosities.

 

[Vaca]

Yes, very true!

 

[PimTac]

https://www.bobistheoilguy.com/viscosity-charts/

 

[Powerglide]

Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.

 

[1JZ_E46]

Add in the temperature factor, and some 30-grade users are into 20-grade territory depending on oil temps, and vice versa.

 

[Snagglefoot]

Originally Posted By: Powerglide
Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.


Blunt but true.

 

[dwendt44]

And let's not forget that each 'grade' has
a span. Meaning that you can have a 'thin' 30 weight
or a 'thick' 30.
IIRC the classic German Castrol was on the thick side
of 30. A 'thin' 30 could shear down to a 20 in short
order.


My 2¢

 

[ARCOgraphite]

Originally Posted By: Powerglide
Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.


You telling me I'm delusional?

I guess you don't understand viscometrics or engines.

A difference of 1.0cP in HTHS metric would insure short service FAILURE of a target engine designed for A5 30 grade (min HTHS 2.9cP).

Now have an Ale, not some girly Lager.

 

[A_Harman]

It's interesting to think about the variation of viscosity with temperature. If you consider the same Mobil 1 Advanced Fuel Economy 0w20, it will have a viscosity of 12.97 cSt at 81.5C, which is the same as the 0w40 FS at 100C.

 

[GR_CoB]

Originally Posted By: Powerglide
Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.

Some of us score "average" or below average on hearing test, and some of us have a hearing that is waaaay above average. Some of us can feel a bean through seven mattresses, while others won't feel a rock through a blanket they're laying on. Just because your senses are on the low end of the spectrum - doesn't mean that everyone is the same way.

Case on point from personal experience:
- 2006 Pontiac Vibe AWD with a 1.8L 1ZZ-FE Toyota engine and drivetrain. With most 5w30s and some 5w40/0w40 oils it did 0-60mph in 18-18.8 seconds. Painfully slow, I know. (FWD version is much peppier) BUT with Valvoline MST 5w40 or with Castrol 5w40 Professional that 0-60mph figure moved to 20-21 seconds. Measured with GPS on the same straight road, same temps, about 930ft above sea level.

 

[ZeeOSix]

Originally Posted By: A_Harman
It's interesting to think about the variation of viscosity with temperature. If you consider the same Mobil 1 Advanced Fuel Economy 0w20, it will have a viscosity of 12.97 cSt at 81.5C, which is the same as the 0w40 FS at 100C.


Yep, in that case you're probably losing a whole whopping 1/2 HP at WOT if the oil is at 81.5 C vs 100 C.

I don't see how any engine is going to feel "sluggish" at operating tempetature based on the oil viscosity used. Now if an engine was cold started in Alaska at -25 F and dynoed with cold oil then there would be a noticeable difference in power output.

 

[benjy]

oil types being similar higher viscosity oils protect better especially in extreme conditions, lower viscosities "can" help performance, hence the 3-1 oils recommended today for that little xtra mpg at the expense of a longer lasting engine. NHRA Pro Stockers run "special" race only 5W oils because performance is ALL that matters!! todays smaller low power engines NEED all the help they can get as they are tuned for MPG's + the EPA!!!!!

 

[OVERKILL]

Originally Posted By: Vladiator
Originally Posted By: Powerglide
Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.

Some of us score "average" or below average on hearing test, and some of us have a hearing that is waaaay above average. Some of us can feel a bean through seven mattresses, while others won't feel a rock through a blanket they're laying on. Just because your senses are on the low end of the spectrum - doesn't mean that everyone is the same way.

Case on point from personal experience:
- 2006 Pontiac Vibe AWD with a 1.8L 1ZZ-FE Toyota engine and drivetrain. With most 5w30s and some 5w40/0w40 oils it did 0-60mph in 18-18.8 seconds. Painfully slow, I know. (FWD version is much peppier) BUT with Valvoline MST 5w40 or with Castrol 5w40 Professional that 0-60mph figure moved to 20-21 seconds. Measured with GPS on the same straight road, same temps, about 930ft above sea level.


Because this is outrageous, I figured I'd plug those numbers into a calculator to get an idea as to the power difference you are claiming to experience between oils of the same grade. Calculator can be found here: https://www.carspecs.us/calculator/0-60

Specs I'm using are from here: Motortrend 2006 Pontiac Vibe specs and here: Auto123 AWD Vibe specs
HP: 123
Curb weight: 1350 kg/2976lbs

Assuming a 180lb driver and 50lbs of fuel we are at 3,206lbs, which yields a 0-60 of 9.9 seconds, which, based on what I can find via some limited searching should be about right.

So, just to get your base figure of 18 seconds I had to drop the specific output to 55HP. Then, to get that to 21 seconds I had to drop it further to 45HP.

I would advise you take it to a drag strip and get some actual numbers, because these seem completely out to lunch

Your car is ~70HP off from where it should be based on your "timed" 0-60 figures, which casts some serious doubt on the validity of any of that claimed "data".

 

[Oildudeny]

What am I missing?

My manual and cap says 0w20, thats what goes in. I don't think no more than that. If 0w20 were not available in goes 5w20 because the manufacturer says it can be used until the next oil change service.

 

[69GTX]

Originally Posted By: Powerglide
Yep, and anyone that says “my car runs much smoother on xxw-30 than xxw-20” is delusional. Same with “my car feels kinda sluggish on QS xx-40. So I switched to Pennzoil conventional xx-30 and it’s sooo much peppier”. Get your head checked, have a beer and worry about something else.


From purely a physics and fluid flow standpoint there HAS to be an oil grade (ie xW-YX) that is OPTIMUM for each vehicle, that maximizes hp and other factors, at various conditions, including ambient temps, etc. Now whether each one of us can feel this in our tushes is another story. I have no doubts someone could in comparing say a 20 vs 40 grade in a performance coupe. Over the 24 hrs of Lemans, I'd bet it makes a huge difference. Driving on the Autobahn or 3,000 miles across the USA, it probably matters too. Some engines just don't like to run on 40 grades...just like others don't prefer 20 grades. Ford designed my daily driver on 30 grade. Yet today Ford recommends 20 grade...and certainly others have used 40 grades successfully. One of those 3 is optimum for engine peak performance, longevity, and safety margins.

Undoubtedly, given a proper testing machine, the differences could be quantified. Whether it's worth the cost and time to do so is also another story. In a Z06 Vette racing, I'm sure there's a HP and overall performance peak and optimal safety margin using one of these: 20, 30, 40, or even 50 grades. They all can't work equally well other than sedate daily driving in moderate ambient temps.

 

[ZeeOSix]

Originally Posted By: Vaca
The SAE weights - 20, 30, 40, 50, etc - are not proportional to the actual viscosity they are are indicating. For instance, a typical 20 weight oil does not have half the viscosity of a typical 40 weight oil.

Looking at the numbers for two commonly used (and discussed here on BITOG) oils we find Mobil 1 Advanced Fuel Economy 0w20 has a 100C viscosity of 8.7 which is two-thirds as thick as the 12.9 of Mobil 1 0w-40 FS.

Looking at the HTHS measurement we find the difference between these two oils is even narrower, 2.7 of the 0w-20 is three-quarters as thick as the 3.6 of the 0w-40.

While obviously there is a difference between these two oils; the difference may not be as large as some of the thick/thin arguers make it out to be.


When the Viscosity vs Temperature is plotted it shows a better picture. You can obviously see why they came up with a "W" rating for cold temperature viscosity.

Two 5W-20 and two 5w30 oils plotted between 0 and 100 C.


Those same oils plotted between 80 and 180 C to expand the viscosity scale for better comparison. 150 C is the temperature that the HTSH is measured at.

 

[OVERKILL]

Originally Posted By: 69GTX
From purely a physics and fluid flow standpoint there HAS to be an oil grade (ie xW-YX) that is OPTIMUM for each vehicle, that maximizes hp and other factors, at various conditions, including ambient temps, etc.


What you are describing is the very crux of the adage "as thin as possible, as thick as necessary". It binds to grade only in the sense that that's one of the variables. What you are looking for is a viscosity that is thick enough to avoid bearing to journal contact under the most extreme conditions, but no thicker. Grade selection is but one parameter here. HTHS is more telling and both are bound to the temperature of the lubricant.

If you can keep the oil cooler, you can keep the spec viscosity lower while still retaining sufficient protection. Conversely, if you cannot or choose not to strictly control temp, a higher margin of viscosity reserve is necessary.


Originally Posted By: 69GTX
Now whether each one of us can feel this in our tushes is another story. I have no doubts someone could in comparing say a 20 vs 40 grade in a performance coupe. Over the 24 hrs of Lemans, I'd bet it makes a huge difference. Driving on the Autobahn or 3,000 miles across the USA, it probably matters too. Some engines just don't like to run on 40 grades...just like others don't prefer 20 grades. Ford designed my daily driver on 30 grade. Yet today Ford recommends 20 grade...and certainly others have used 40 grades successfully. One of those 3 is optimum for engine peak performance, longevity, and safety margins.


From the calculations I recall Shannow doing, one would be pretty hard pressed to "feel the difference" as the actual difference in losses, in KW, is not very high. Like we are talking headlights difference at operating temperature IIRC (Shannow, feel free to correct me here).

Originally Posted By: 69GTX
Undoubtedly, given a proper testing machine, the differences could be quantified. Whether it's worth the cost and time to do so is also another story. In a Z06 Vette racing, I'm sure there's a HP and overall performance peak and optimal safety margin using one of these: 20, 30, 40, or even 50 grades. They all can't work equally well other than sedate daily driving in moderate ambient temps.


The differences are qualified, hence the focus of CAFE and fractions of a MPG difference. As fuel economy goes up the margin of protection goes down. As long as it remains within the "safe" envelope for operation, no harm no foul. Controls on oil temperature and thermal castration mechanisms have made a presence here to ensure that this safety margin, which has been decreased, remains adequate.

On the Corvette situation, since CAFE is not a primary driver, GM specs different oils for different operating conditions. One is "optimal" for typical street use (now 0w-40) and the other for track (15w-50). Ford did similar variations, though without the dual-spec, on the Mustang GT with the difference being the presence of the "Track Pack" package which changed the spec from 5w-20 to 5w-50 and included an oil cooler.

 

[Kawiguy454]

Not arguing one way or the other. Growing up the guy down the street had an ~800HP hemi cuda pro stocker he would bracket race. He said they put conventional oil in the differential and if they needed to cut the bracket really close they would change it out to Synthetic of I assume the same weight. This change only to the diff was worth .1 second in quarter mile and it was repeatable enough to help win a lot of races.

I dont think engine oil is quite the same thing as it is not the direct interface between meshing gear teeth but there must be differences. Wether your perfectly calibrated hiney G-Meter can tell is a bit of a stretch for me.

 

[OVERKILL]

Originally Posted By: Kawiguy454
Not arguing one way or the other. Growing up the guy down the street had an ~800HP hemi cuda pro stocker he would bracket race. He said they put conventional oil in the differential and if they needed to cut the bracket really close they would change it out to Synthetic of I assume the same weight. This change only to the diff was worth .1 second in quarter mile and it was repeatable enough to help win a lot of races.

I dont think engine oil is quite the same thing as it is not the direct interface between meshing gear teeth but there must be differences. Wether your perfectly calibrated hiney G-Meter can tell is a bit of a stretch for me.


That doesn't sound unreasonable. You'd never feel .1 of a second, but you would of course see it on the time slip. Every little thing counts in drag racing. An aluminum driveshaft made my Mustang faster, but obviously didn't increase the power output for example.