Thinner oil, but worse MPG - science or fiction?

[FatBloke007]

Hello all, new member here. Had some interesting observations which may be entirely plausible, however I can't find any reliable information to help me make sense of it.. hence I thought I'd ask.
The situation is the following:
- Car is a 2011 Volvo XC90 with the 4.4L Yamaha built V8. DOHC with VVT. Current mileage 83.7k.
- I've owned the car since early October last year. Dealer provided an oil & filter change prior to handing over to me. My assumption is the dealer filled up with 0w30.
- Over the past 2000miles I have performed 2 oil drains via the dipstick with a Vacuum pump, each time extracting ~5L of the ~6.7L in place.
- I refilled with Shell Helix 0w40 as per https://www.shell-livedocs.com/data/published/en-GB/0e8580ed-9627-4d62-ad0d-c904a7a03a0d.pdf
- My thinking was this oil is relatively cheap, high quality and may do a decent job of 'cleaning up' whatever lies within. (This notion may well nonsense?)
- My intention was to run the car with a 0w30 in the winter. Hence I have recently again removed 5L via the dipstick, and refilled with Shell 0w30 ECT C2/C3 as per https://www.shell-livedocs.com/data/published/en-GB/e7ec61ff-5983-4ab2-b8c9-b240f654f5be.pdf
- Filter has not been changed on any of my drain/fills.
- This 0w30 oil has a different additive package as far as I can tell.. Boron heavy.

So the car currently largely runs on 0w30. I expected slightly improved fuel economy overall, with reduced losses on cold starts.. however, I have consistently observed poorer mpg on my regular 15-20mile journeys, since changing to the 0w30. I appreciate there are many variables at play when considering fuel economy.
My question ultimately is, all else being equal, is it possible for an engine to be less efficient with a lighter oil weight in operation?

 

[Rand]

Seasonal variance (weather) much greater impact than oil

 

[facility1]

hard to track mpg in winter, and there is no real reason to use 0w-40 ?. 5w-30 year-round would work just fine, Shell makes a fine product to note for your car.

 

[fdcg27]

I dunno.
I do know that in the past I've gone up a grade on cars we had years ago and noticed no loss in fuel economy in colder weather.

 

[fantastic]

What's the data? How many miles have you tracked of each grade etc. I did a 4,500 mile run, on the 3.2L XC90 (Ford Whales) that came in the states, on 5w-30 vs 5w-40. The 5w-40 had more weight due to kids, more winter idling, & it was only 0.30 mile per gallon difference. With that V8 It could be real easy to get lower fuel economy I'd imagine. Ford went to Yamaha which they'd done before. Enjoy it while you can.

Found my previous post

https://bobistheoilguy.com/forums/t...nt-oil-viscosities.394933/page-2#post-7230858

 

[BMWTurboDzl]

Hello all, new member here. Had some interesting observations which may be entirely plausible, however I can't find any reliable information to help me make sense of it.. hence I thought I'd ask.
The situation is the following:
- Car is a 2011 Volvo XC90 with the 4.4L Yamaha built V8. DOHC with VVT. Current mileage 83.7k.
- I've owned the car since early October last year. Dealer provided an oil & filter change prior to handing over to me. My assumption is the dealer filled up with 0w30.
- Over the past 2000miles I have performed 2 oil drains via the dipstick with a Vacuum pump, each time extracting ~5L of the ~6.7L in place.
- I refilled with Shell Helix 0w40 as per https://www.shell-livedocs.com/data/published/en-GB/0e8580ed-9627-4d62-ad0d-c904a7a03a0d.pdf
- My thinking was this oil is relatively cheap, high quality and may do a decent job of 'cleaning up' whatever lies within. (This notion may well nonsense?)
- My intention was to run the car with a 0w30 in the winter. Hence I have recently again removed 5L via the dipstick, and refilled with Shell 0w30 ECT C2/C3 as per https://www.shell-livedocs.com/data/published/en-GB/e7ec61ff-5983-4ab2-b8c9-b240f654f5be.pdf
- Filter has not been changed on any of my drain/fills.
- This 0w30 oil has a different additive package as far as I can tell.. Boron heavy.

So the car currently largely runs on 0w30. I expected slightly improved fuel economy overall, with reduced losses on cold starts.. however, I have consistently observed poorer mpg on my regular 15-20mile journeys, since changing to the 0w30. I appreciate there are many variables at play when considering fuel economy.
My question ultimately is, all else being equal, is it possible for an engine to be less efficient with a lighter oil weight in operation?

No its not possible

 

[fantastic]

No its not possible

If all things are equal but it may not have been the last few tanks. I'd think it wouldn't be that hard to get worse MPG on a 20 grade vs a 30 grade if one had a leaded foot on the 20 as an example.

 

[TiGeo]

Because the 0W-30 and 0W-40 have the same/close HTHS and viscosity is similar. The 0W-30 is a thick 30 and the 0W-40 is a thin 40. Both have a zero winter grade so not sure why you aren't just running the 0W-40 year around?

 

[altaylar]

Because the 0W-30 and 0W-40 have the same/close HTHS and viscosity is similar. The 0W-30 is a thick 30 and the 0W-40 is a thin 40. Both have a zero winter grade so not sure why you aren't just running the 0W-40 year around?

Exactly. There is not really much of a difference between those two, even though by their naming, they might appear different.

You could still expect slighlty better MPG but not big enough to be noticed by you. Your tire pressures drop in winter and that will probably effect your MPG more than siwtching between these two oils.

 

[altaylar]

Also another point is, notice that you are changing about 3 quarters of your oil each time. I think it would make much more sense to stick with a single product year around, rather than running a mix all the time. As a general rule of thumb, any of those two products is a better performer than a mix of theirs

 

[FatBloke007]

What's the data? How many miles have you tracked of each grade etc. I did a 4,500 mile run, on the 3.2L XC90 (Ford Whales) that came in the states, on 5w-30 vs 5w-40. The 5w-40 had more weight due to kids, more winter idling, & it was only 0.30 mile per gallon difference. With that V8 It could be real easy to get lower fuel economy I'd imagine. Ford went to Yamaha which they'd done before. Enjoy it while you can.

Found my previous post

https://bobistheoilguy.com/forums/t...nt-oil-viscosities.394933/page-2#post-7230858

The data are poor, largely numbers I've eyeballed, but as I make these journeys regularly and will reset the 'mpg gauge' on these runs for my own interest. The car is still relatively new to me, hence I'm still snooping around the engine bay, keeping an eye on a few variables etc. The new car 'terror phase' essentially. In similar -2 to 4deg C weather range, same tire pressures, running with the 0w40 I would see up to 29mpg by the end of the journey. The same exercise yesterday, for example, with the 0w30 in play never went above 27mpg. The V8 can be relatively frugal, but if you put your foot down it will guzzle hard. Sounds wonderful. It may well be as trivial as differences in right foot action at particular instances of the journey - over 20 miles these guzzling events will make a decent contribution to the overall average.

 

[FatBloke007]

Because the 0W-30 and 0W-40 have the same/close HTHS and viscosity is similar. The 0W-30 is a thick 30 and the 0W-40 is a thin 40. Both have a zero winter grade so not sure why you aren't just running the 0W-40 year around?

I've probably just been overthinking this. My thoughts were that the 0w30 may be beneficial in winter for the cats, with slightly increased idle durations etc. Also potentially better economy on cold starts. As you point out, maybe there isn't enough of a difference in these oils to justify the swap. They do have very different additive packages however. With this engine being chain driven, again maybe I'm better sticking with the 0w40 as I presume this will have a higher weight base oil.

 

[Titan]

The car will provide decreased MPG simply due to the much colder weather. Longer warm-up times for the engine and the fuel trim, increased density of the air that the car has to push aside, tire pressure drops (unless you stay right on it every time the temp drops). As someone else pointed out, there isn't enough difference in viscosity between your two choices to be noticeable within the noise of all the other variables...even if the temperature had been constant.

 

[fantastic]

I've probably just been overthinking this. My thoughts were that the 0w30 may be beneficial in winter for the cats, with slightly increased idle durations etc. Also potentially better economy on cold starts. As you point out, maybe there isn't enough of a difference in these oils to justify the swap. They do have very different additive packages however. With this engine being chain driven, again maybe I'm better sticking with the 0w40 as I presume this will have a higher weight base oil.

The 0w-30 ESP could be easier on the Catalytic converters but I'm not familiar with those Pennzoil product additives. I don't know what the outcome will be on my 3.2L but I use Mobil ESP 0w-40 anyways. I know the 5w-30 & 0w-30 Mobil ESP has slightly less P in it.

 

[TiGeo]

The concern about a full-SAPS Euro oil causing cat issues is unfounded IMHO. Where are all these Euro cars that have been running Mobil 1 0W-40 (or whatever brand of oil that is the "same") for all these years with clogged up cats? Crickets....

Just run the 0W-40 and sleep easy.

 

[JAG]

There are many variables as has been said. In a tightly controlled experiment, with 0W-30 and 0W-40 having the same additive package, except for VII concentration, and both oils having similar HTHS viscosity, it is possible for the 0W-40 to provide better fuel economy. A study similar to this situation found that because the shear rate in some parts of the engine significantly exceeded 1e6/second, the oil with the wider-spread viscosity grade, analogous to your 0W-40, had a lower weighted-average dynamic viscosity than the oil with narrower-spread viscosity grade.

It sounds like you didn’t control the variables enough to be able to be confident that the observed MPG changes are due to the two oils.

 

[BMWTurboDzl]

The concern about a full-SAPS Euro oil causing cat issues is unfounded IMHO. Where are all these Euro cars that have been running Mobil 1 0W-40 (or whatever brand of oil that is the "same") for all these years with clogged up cats? Crickets....

Just run the 0W-40 and sleep easy.

Perhaps he's talking about OPF?

 

[Trashman]

Hello all, new member here. Had some interesting observations which may be entirely plausible, however I can't find any reliable information to help me make sense of it.. hence I thought I'd ask.
The situation is the following:
- Car is a 2011 Volvo XC90 with the 4.4L Yamaha built V8. DOHC with VVT. Current mileage 83.7k.
- I've owned the car since early October last year. Dealer provided an oil & filter change prior to handing over to me. My assumption is the dealer filled up with 0w30.
- Over the past 2000miles I have performed 2 oil drains via the dipstick with a Vacuum pump, each time extracting ~5L of the ~6.7L in place.
- I refilled with Shell Helix 0w40 as per https://www.shell-livedocs.com/data/published/en-GB/0e8580ed-9627-4d62-ad0d-c904a7a03a0d.pdf
- My thinking was this oil is relatively cheap, high quality and may do a decent job of 'cleaning up' whatever lies within. (This notion may well nonsense?)
- My intention was to run the car with a 0w30 in the winter. Hence I have recently again removed 5L via the dipstick, and refilled with Shell 0w30 ECT C2/C3 as per https://www.shell-livedocs.com/data/published/en-GB/e7ec61ff-5983-4ab2-b8c9-b240f654f5be.pdf
- Filter has not been changed on any of my drain/fills.
- This 0w30 oil has a different additive package as far as I can tell.. Boron heavy.

So the car currently largely runs on 0w30. I expected slightly improved fuel economy overall, with reduced losses on cold starts.. however, I have consistently observed poorer mpg on my regular 15-20mile journeys, since changing to the 0w30. I appreciate there are many variables at play when considering fuel economy.
My question ultimately is, all else being equal, is it possible for an engine to be less efficient with a lighter oil weight in operation?

My personal experience on our vehicles has always been that they have gotten slightly better MPG’s with thicker oil than thinner oil. You will definitely get the full spectrum of opinions and experiences here, the best thing to do would be to try a few different oils/weights that interest you and see how your vehicle does with each and compare. If you aren’t too happy with the 0W30, maybe try a 0w40, 5W40 or 5W30 next time and see if it’s an improvement, a step in the wrong direction, or no noticeable difference at all. Welcome to BITOG by the way

 

[CleanSump]

The concern about a full-SAPS Euro oil causing cat issues is unfounded IMHO. Where are all these Euro cars that have been running Mobil 1 0W-40 (or whatever brand of oil that is the "same") for all these years with clogged up cats? Crickets....

Just run the 0W-40 and sleep easy.

If not equipped with a Gas Particulate Filter or Diesel Particulate Filter, high Sulphated Ash Phosphorus Sulphur (SAPS) isn't a concern. It's not likely to clog a standard catalytic converter unless you're burning large amounts of oil.

 

[FatBloke007]

Thanks to all for you thought & input - very interesting to hear.