Oil viscosity and fuel economy

[BuickGN]

I noted a long time ago that I get better mileage in the TL going from a 0w or 5w-20 (can't remember) to Amsoil's straight 30. I fully expected it to feel a little sluggish but I would swear it picked up a couple hp. I didn't make a big deal about the fuel economy because it was in the 1-2mpg range which could be the margin of error. However, there's no chance whatsoever that mileage went down with the thicker oil.

You may be trading ever so slightly more friction and drag for a better ring seal. It wouldn't take much in the way of better ring seal increasing engine efficiency to trumph the minor difference in oil drag.

I know there are tons of variables other than viscosity when changing oils like FM, but I would love to see a study on HTHS and ring seal.

 

[fdcg27]

I have wondered this myself.
Does better ring seal compensate for more drag?
I have never seen any major loss in fuel economy from going a couple of grades thicker.
Makes you wonder.

 

[friendly_jacek]

Originally Posted By: buster

There is no way a 50 grade will have better fuel economy than a 30 grade with a HT/HS that low.


Yes, there is a way. While lower viscosity decreases energy loss in the piston/ring/liner area (due to lower oil thickness), it INCREASES energy loss (and sometimes wear) in the cam/valvetrain area. This is because boundary lubrication has higher friction coefficient.

This is why lower viscosity was not feasible in older engines. Newer engine designs have much lower friction in the cam/valvetrain area (roller followers being the best example), and the net effect is lower energy loss with lower viscosity.

I'm not saying this accounts for the OP observation, because the pump volume method for MPG measurements is too inaccurate to make any conclusions.

 

[buster]

Thanks, I was not aware of that. Interesting.

 

[Shannow]

Originally Posted By: friendly_jacek
This is why lower viscosity was not feasible in older engines.


1968 SBCs and Holden V-8s, the oil specs ranged from 10W-20 to 10W-30, to straight 30...isn't that lowish ?

For a 1950s design engine ?

 

[XS650]

Originally Posted By: Shannow
Originally Posted By: friendly_jacek
This is why lower viscosity was not feasible in older engines.


1968 SBCs and Holden V-8s, the oil specs ranged from 10W-20 to 10W-30, to straight 30...isn't that lowish ?

For a 1950s design engine ?


20 weight in the US car owners manual goes back to the 1940s on some cars, maybe earlier.

1940 Oldsmobile was 20 weight for normal weather, 10 for colder. I think that was common then.

1934 Chevy was 20 weight too.
http://chevy.oldcarmanualproject.com/chevyowner/34om52.htm

 

[buster]

I'm going to run Mobil 1 0w-40 next and see how it impacts MPG.

 

[Shannow]

There were bottles of 0W-40 M1 sold down here that had the energy conserving label on the bottle.

They don't any more.

 

[aquariuscsm]

I get more power (in the upper rpm band) with a thicker oil. It`s really noticeable on high speed highway accelerations. I also get better highway mileage over long high speed drives (80+ mph which you have to do here on the interstates or you`ll get run over!). I noticed it on the usual 100 mile stretch between my house and my dad`s place. Another thing I notice with a thicker oil,is that if I use the clutch to slow my car down (engine braking) I can really feel the engine "grabbing the wheels" and slowing it down better than with a thin oil. Imo,thicker oils create better compression.

 

[buster]

aqua, just curious what heavier oils have you tried and liked? Have you tried M1 0w40?

 

[aquariuscsm]

Originally Posted By: buster
aqua, just curious what heavier oils have you tried and liked? Have you tried M1 0w40?


Man it seems like I`ve tried them all. GTX,RP,Pennzoil yb,Valvoline wb,Valvoline VR1 (in 20W50) and M1 15W50. My faves out of the bunch,VR1,Pennz yb,and RP. I had MJ from Mobil actually not recommend the 0W40,BUT recommend the 10W30,and then go on to say the 15W50 was too thick. I don`t think MJ knows what he`s talking about. I`ve come VERY close to giving the M1 0W40 a go.

 

[BuickGN]

I need a car to try the 0w-40 out in. I really like the specs, maybe I'll run it in the Murano but I have way too much Redline 5w-30 now.

 

[aquariuscsm]

Once it gets good and hot here (our famous 108F summers) I`m going to try out my Pennzoil GT 25W50.

 

[mechtech2]

Some common engines from the 1930s called for 20W.
And they recommended adding a bit of gas to the mix for winter use.

So forget about light oils being new or suitable only for modern engines.

Heavier oils cause the pump to work harder, have more internal friction, and have more drag as the crank , rods, etc. slosh through it.

 

[sbergman27]

Originally Posted By: mechtech2
Some common engines from the 1930s called for 20W. And they recommended adding a bit of gas to the mix for winter use. So forget about light oils being new or suitable only for modern engines.

They didn't have multi-vis back then and oil viscosities were all over the board depending upon temperature. A particularly cool summer morning could make a car running a 30 weight virtually unstartable.

How many miles did car owners expect out of their engines running the 20 weight oil with a little gasoline mixed in?

Would modern owners be happy with the same engine life expectancies?

 

[fdcg27]

I wanted to give a quick update.
In the 1773 miles that the '99 Accord has been on the M1 15W-50, it has used 58.1 gallons, for an average fuel economy of a hair over 30.5 mpg.
I have just put the same oil in the '97 Accord, for which I have good numbers on a mix of M1 5W-20 and M1 5W-30.
We'll see how much worse the 15W-50 does in the '97

 

[sangyup81]

Originally Posted By: fdcg27
I wanted to give a quick update.
In the 1773 miles that the '99 Accord has been on the M1 15W-50, it has used 58.1 gallons, for an average fuel economy of a hair over 30.5 mpg.
I have just put the same oil in the '97 Accord, for which I have good numbers on a mix of M1 5W-20 and M1 5W-30.
We'll see how much worse the 15W-50 does in the '97


I don't think there is anything but a microscopic difference in fuel economy for the highway portions. How much city driving do you do?

 

[fdcg27]

Not much.
Three miles of my commute is through a small city, but you can often time the lights and avoid more than one or two complete stops.
The first five miles are four lane divided highway, while the last seventeen consists of rural two lane.
My thinking was in line with yours, in that I doubted that the heavier oil would make any significant difference in fuel economy given the way I use the car.

 

[oggb]

I've used the following oils with the following gas mileage:

Mobil 1 5w30 @ 22-24 mpg mostly city, 29 mpg mostly highway, 26 average.
Rotella Synthetic 5w40 @ see above ^^^
Pennzoil Platinum 5w30 @ see above ^^^
Rotella T 15w40 @ see above ^^^
Devlac 1300S 15w40 @ see above ^^^ (but I swear my average MPG might've gone up very slightly)

So yeah, oil weight vs. MPG is complete [censored] in my experiences.

 

[ekpolk]

Originally Posted By: friendly_jacek
Originally Posted By: buster

There is no way a 50 grade will have better fuel economy than a 30 grade with a HT/HS that low.


Yes, there is a way. While lower viscosity decreases energy loss in the piston/ring/liner area (due to lower oil thickness), it INCREASES energy loss (and sometimes wear) in the cam/valvetrain area. This is because boundary lubrication has higher friction coefficient.

This is why lower viscosity was not feasible in older engines. Newer engine designs have much lower friction in the cam/valvetrain area (roller followers being the best example), and the net effect is lower energy loss with lower viscosity.

I'm not saying this accounts for the OP observation, because the pump volume method for MPG measurements is too inaccurate to make any conclusions.


Ooooooooo -- blasphemer!!! You should expect that one night, several hours after you peacefully laid your head on your pillow, looking forward to a good night's sleep, a team of sludge-black-clad Ninjas, on the double-secret government payroll, will swiftly and silently invade your home, cart you off, finish you off, and bury you in a New Jersey landfill, never to be seen again. Questioning the current low-vis dogma is, well, ... I shall say no more, hoping to ward off a Ninja visit myself.

Friendly, Friendly, you still out there? ? ?