Thanks. I guess to me it seems like you're really cutting down on engine protection and for nothing. Can't wrap my head around why the push for change in specs. I didn't know if I'd see a real gain in jumping from my current oil to the lighter ones. I didn't want to and don't like the thought of it.
How much does oil viscosity really change mpg?
- Thread starter FlyingTexan
- Start date
I don’t know how the B58 manages oil temperature, but that’s key to the performance of any oil, and particularly to the performance of a 0W20. My Tundra, for example, specifies a 0W20 and has a fairly sophisticated water/oil cooler as part of the filter mount. Didn’t expect that on a regular truck with a V-8, but there it is. All the Volvos have an integral water/oil cooler built into the sump, been that way for decades. Both MB have very capable air/oil coolers. I’m willing to bet that the B58 has a sophisticated oil temperature management system, and in that case, I wouldn’t worry much about a 0W20.
Fractions of tenths of an mpg, in most cases, on a sample size of one (your vehicle). Environmental factors (temps, winds, tire pressures, inclined or declined road surfaces, etc) have far more impact than a couple cSt of viscosity or change in HTHS does.
Depends on equipment.
But even basic B58 has a very complex oil heating/cooling system.
1. All have fluid heat exchangers to warm up oil fast (the one you are referring to in Tundra). Even in old BMWs that do not have heat exchangers, a coolant line passes through the oil filter housing).
2. Thermostat is electronically controlled and has 4 different types of operation that are between HWY driving (high coolant temperature) and track driving, where the thermostat keeps coolant temperature as low as possible (previous engines, since N generation in 2004 had an electric water pump that does the same, like mine).
3. There is then radiator type (or two depending whether it is M Sport or S58 M model) oil cooler(s).
4. It has two cooling systems: one for engine one for intercooler.
This ^^^ is the key. Automakers are impacted by the federal gov't with either credits or penalties based on their FLEET fuel economy so any tenth of an MPG increase they get out of one car is extrapolated across their entire fleet.
That is marketing BS. Because LL01 can have an HTHS of 3.5mpas, and LL01FE can have an HTHS of 3.49mpas.
What they did is they compared the lowest possible HTHS in LL01FE and the highest possible HTHS in LL01.
That is like when oil companies say: our synthetic oils clean xxx times better than average mineral oil.
Well Redline runs on the thick side, it's possible there was better sealing and less blow by. Here is a oil that won't be broken down like your Grp3 oils as much. Probably runs cleaner too. You also have to look at operating temperature and driving style.
Also I suppose, all things equal including wasteful habits, the cold start and extended idling is the one instance where the differences in oil viscosity has the biggest effect? The oil stays cool 10-20 minutes , and driving the oil pump is must be a large part of the idle load with oil at -10C up to maybe 40C?
I guess if you do mostly cold start short tripping you could see a significant difference in fuel economy with thinner oil.
Also I think the effect of oil viscosity depends on your vehicles cruising rpm. At 60mph my Focus is near 2500 rpm, but the Outback is at 1600 rpm, so I would think the Focus would see more effect of lower viscosity oil than the Outback.
Also I guess it depends on if your vehicle has a variable speed or displacement oil pump. I would assume the electric ones are programmed to maximize efficiency by pumping the least amount they can get away with, given oil temp, engine rpm, and maybe throttle position?
So if you do cold start, short hwy trips an a manual trans car, running 0W16 vs 5W40 might really be noticable?
Generally* speaking you have to engineer an engine to use a thinner grade rather than a thicker grade. So while the B-series did initially use LL01/LL04 it doesn't mean that it was engineered to use only LL01/LL04. I hope that makes sense.
Secondly, all markets are different. There are differences in fuel quality (ex, sulphur levels), emissions regulations, and operating environment. For example in the US beginning in 2015 LL01FE became standard fill as N-series engines were slowly replaced by the B-series. When the US moved to ULSG in 2020 BMW still has not moved from LL01FE to a low-saps 30 grade LL12FE+ even though the B-series get the Low-SAPs 20 grade. LL04/LL12FE has been available in parts of the EU for a decade or more.
People really overestimate the performance advantage of a heavier oil vs modern 20 grade in daily-to-day driving. It's the engineering that matters.
All that being said I do follow a BMW engine builder out of Germany and they have commented on chain guide wear with the B-series so maybe the 20 grades aren't that great for the autobahn but we don't know what oil the customer was using anyways.
*There was always a lot of talk about BMW bearings being too tight for 10w60 with regards to the naturally aspirated M-engines. Some owners have good results running 5w-50
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You can look at the fuel economy test requirements for different oil grades in various oil standards.
Here are the requirements by grade for the test used for API SP:
The difference between an xW-20 and xW-30 is 0.7%. This is an average of the FEI1 test with lightly aged oil, where the difference is 1.1%, and the FEI2 test with heavily aged oil, where the difference is 0.3%.
In the VW standards, a 0W-30 requires 0.5% better fuel economy than a 5W-30.
In the MB standards, an xW-30 requires 0.5-1.2% better fuel economy than an xW-40.
The differences would be larger when the oil is cold, or at light engine loads or idle.
Here are the requirements by grade for the test used for API SP:
The difference between an xW-20 and xW-30 is 0.7%. This is an average of the FEI1 test with lightly aged oil, where the difference is 1.1%, and the FEI2 test with heavily aged oil, where the difference is 0.3%.
In the VW standards, a 0W-30 requires 0.5% better fuel economy than a 5W-30.
In the MB standards, an xW-30 requires 0.5-1.2% better fuel economy than an xW-40.
The differences would be larger when the oil is cold, or at light engine loads or idle.
Patman
Staff member
That Toyota engineer is spouting nonsense then. The difference in viscosity between a 0w20 and a 0w16 is miniscule. Just look at the specs of M1 0w20 vs M1 0w16 for instance, the difference is 8.2 cst at 100c vs 7.6 cst at 100c. That's not even going to change your MPG by 0.2% let alone 2-3%.
Saving a small amount of fuel doesn't mean much per vehicle but it constitutes a considerable quantity over millions of vehicles.
I'll do one less gear banging session from 0 to 100 per gas tank and keep my 5W-30 vs 5W-20.
Research Shows Oil Viscosity Affects Fuel Economy
You could save as much as 1 percent on your fuel economy simply by switching from a 15W-40 engine oil to a 10W-30 engine oil, according to new research from Chevron Oronitewww.truckinginfo.com
To add, another aspect is the friction modifier add pack. Possible that some oils having the same exact HTHS viscosity can have different friction levels in use. The loss in fuel economy is dependent on both the power put into shearing the oil film between moving parts, and also the rubbing friction between moving parts in the mixed and boundary layer realms of lubrication.
CeraTec by LiquiMoly (a friction modifier) actually did some tests showing a HP increase on the dyno due to the reduction in friction between moving parts. That would also equate to better fuel economy on the road. CeraTec also seems to cure the ticking almost instantly after adding it in the Ford Coyote 5.0L V8 per many people's reports. I've also come to the conclusion that the Coyote tick is sensitive to and caused by the friction level of the oil between moving parts. If the friction level is too high, it kicks off the ticking - most likely the rod big ends moving side-to-side on the crank journals.
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Many a mickle makes a muckle.I'll do one less gear banging session from 0 to 100 per gas tank and keep my 5W-30 vs 5W-20.
Especially tire air pressure. That, and simply combine one trip once every year and it blows away any viscosity difference.
Thank you for the response. I just want to put it out there I’m not here to argue but to learn. For some **** reason I asked one question and it was like lighting a fuse in my brain. I almost wish I went back to knowing nothing and just threw whatever the gas station was selling back in. I guess by trying to understand the industry and why they’re doing what they’re doing I can make better decisions for myself. It’s not that MPG isn’t important to me but more wondering why the drastic change in oil recommendations lately and who they’re recommending them for. I truly find it interesting. Personally I don’t want the govt ever driving the industry. I believe competition breeds excellence. Before this new vehicle I bought I put Shell T6 in everything. But to be honest I knew I wouldn’t keep them forever. This new guy, my grenadier, could very well be my last vehicle. My grandmother, father, and aunt all have had Alzheimer’s at roughly 60 and the odds aren’t good so I bought this thing knowing it could be my last and the aviator in me makes me dig into everything systems related. So once you started responding to a question a while back I found myself debating if I should have gone into petroleum engineering instead lol.
Heck, with only 1% savings from going from 15w40 to 10w30, I’ll take the full-size spare from the trunk, toss it on the garage floor, and keep doing exactly what I’m doing. They must really think people are F’ing dumb with some of the crap they choose to make marketing materials (or dictate policy) with.I'll do one less gear banging session from 0 to 100 per gas tank and keep my 5W-30 vs 5W-20.
So what they’re telling you is, give up somewhere around 20% engine protection to save $3.50 (1 gallon) every month if you drive 24k miles per year at 20mpg… and even less if your vehicle’s current efficiency is greater than 20mpg. So for ~$50 per year savings, you can risk a full engine rebuild or trip to the junkyard! Seems like a great trade!
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