Fuel economy of oil not so simple?

[Ducked]

I'd sort of assumed that, if there was generally a fuel economy benefit (at equilibrium operating temperature) of a low-winter-rating multi-grade with the same nominal viscosity at equilibrium operating temperature, (eg 10W40 versus straight 40) it must be due to a greater susceptibility to temporary shear at equilibrium operating temperature.

Not so?

 

[SonofJoe]

Originally Posted By: Shannow
It's funny, but your monograde 10W20 would warm up quicker than an uber VI 0W20, with more viscous drag in that warmup regime.

Looking at Toyota and Honda stuff, it's the warm-up range that they are really targetting, short tripping.

Do you think that you could make a mono 20 with an HTHS around the 2.6 mark instead of 2.8 to 3 ?

Shannow, I don't have my old box of tricks to answer such questions but I would have guessed you could get 10W20 to at least 2.6 HTHS.

Yes, I know that a lot of OEMs target the 'very low temperature end' of fuel economy and it's here where 0W20's will shine the most and 10W20 won't. However, if I look at my own driving habits, I might typically start the car when it's 10-15°C ambient (so expect the sump temp to be a few degrees higher). The water temperature light goes off after maybe 90 seconds so I know the engine's warming up quickly. As often as not, after 5 - 10 minutes I'm on the motorway and I'm going to guess the oil's equilibrated with the water temp in another 10 minutes because there's so little oil to heat up in my tiny sump.

So say there are three phases from 10°C to 100°C; 10->40, 40->70 & 70->100. A 0W20 will do way better than a 10W20 in that first phase but here's the thing... for a lot of cars, this will be a very short transient phase because this is when the rate of oil heat-up is at it's highest. For phase 2, the relative FE advantage of the 0W20 will still be there but much diminished. For phase 3, I doubt if you will see any FE advantage. If you drive say for one hour or more, the 10W20 will be giving you much the same overall FE as a 0W20.

And here's the big thing...the 10W20 will require cheaper, heavier base oils, less (no??) VII, a lot less DI and it will have a low Noack. For me, these are significant pluses that more than compensate for that small differential in overall FE. At the end of the day, oil FE is a financial benefit from which you have to subtract the differential cost of the oil. If you widen the financial calculation, my instinct is that the numbers will favour a cheap 10W20 over an expensive 0W20.

Finally, remember that engine oil warms up relatively quickly but cools down relatively slowly. If I drive an hour to see my grandson for a few hours, the oil will still be warm when I set off on the return journey. So phase 1 (the one that favours 0W20) may be very short lived on the way back. Given that most human driving involves going somewhere and coming back later, this is probably significant.


PS - I should add that I have a 0W20 in my Suzuki and I'm pleased with it but a 10W20 might be just as good and better in other respects.

 

[Shannow]

Oh, I agree...

messing around with 2.6HTHS and 110VI puts the KV40 at 55, and the KV100 at 8...so it's doable (should have played before asking).

Here's a curve of energy input into oil after starting due to viscous shear, so again, I think that your commentary is spot on.

Something that I didn't realise until relatively recently, there are a bucket of people who drive only a few hundred yards every day...wouldn't matter what oil was in them.

 

[SonofJoe]

I can't speak for other bits of industry but for us, these people were also known as 'Aunt Minnie'. I have absolutely no idea where it originated but we ran a few Aunt Minnie trials, as I recall to look at sump accumulation from regular but very short journeys.

The thing is that whilst Aunt Minnie might, in percentage terms, benefit most from a 0W20 oil, it's wrong to use her as a 'norm setter' because the absolute amount of fuel she and her ilk 'saves' is miniscule. On the other hand, the accumulated Dandad (he can't quite say Grandad yet) Joe's of this world, who might drive a two hour round trip to look after their grandson for a few hours after nursery, probably clock up a significant amount of overall miles. 10W20 might make global sense.


BTW, I am unashamedly green and have been for as long as I can remember. I started my career refining oil and making energy savings any which way you could became as routine as eating & breathing. For me, 'efficiency' is a sign of higher human intelligence. I believe in global warming and I think it's incumbent on us oldies not to stuff as much of the world resources into our greedy fat gobs, just because we can, but to leave behind as much as we can to the generations that follow instead. It pains me to listen to that bouffoned pillock gobbing off in public, telling anyone that's daft enough to listen that it's okay to burn and consume as much as we can today and bugger tomorrow. My perfect grandson deserves better than that...

 

[Shannow]

Originally Posted By: SonofJoe
BTW, I am unashamedly green and have been for as long as I can remember. I started my career refining oil and making energy savings any which way you could became as routine as eating & breathing. For me, 'efficiency' is a sign of higher human intelligence.


That's been my entire career too...more electricity for the same coal burn has been my mantra for a quarter century.

(Don't tell anyone, but my Colorado has a full 5 year carbon offset paid up front)

 

[SonofJoe]

It's funny the things that inform your core values.

Many years ago, I was watching a TV program about The Fall Of Singapore. They interviewed this genial old chap who at the time was one of the young captured British Army POWs. He was recounting his memories of the Death March through Malaya and up into Thailand. He described how they set off at pace with very little to eat or drink. Anyone that fell behind felt the sharp edge of a Japanese sword so there was real pressure to keep up.

It was how (and this is the bit I most remember) he described how the big fit guys, the ones who could under normal circumstances do PT all day long, were the ones that fell away first. After that the medium build blokes collapsed and were despatched. At the end of the march, all that was left were the weedy, scrawny types with sunken chests and whatnot.He was bemused at this and reflected that 'Only the most efficient bodies survived'. I don't why this rang such a strong chord with me but from that moment onwards, 'efficiency in everything' because my mantra.

 

[zeng]

Vehicle fuel economy, engine (mechanical) efficiency and (lubricant drag) frictional losses are being mixed up in the current discussion, IMO.

 

[Mitch Alsup]

I find it continually amazing that the "average" driver (or average BITOG) worries about the FE difference between yyW-xx and zzW-xx oils and whether they should change their oil for that 1%, 2%, 3% gain in FE,


When a few minor corrections of their driving habits can deliver big gains in FE without changing their oils.
I am currently getting 21 MPH in my Ferrari (rated at 17 MPG)
I am currently averaging 19.4 MPG in my GLS (rated at 15 MPG) // averaging = over the entire life of the vehicle.
I am currently averaging 22.1 MPG in my S600 (rated at 15 MPG)
But to some extend, my driving is no where close to "average".

 

[SonofJoe]

Since new, I've averaged 70.0 mpg (imperial) in my little Suzuki. The other week I did 546 miles on 32 litres of unleaded; that's 76.8 mpg. I get that because I only drive at moderate pace, low revs, peak shave acceleration and deceleration, etc etc. My gut feel and background in engine oil design, says to me that low viscosity lubes can contribute a lot more than the odd 1% of fuel economy.

As a matter of policy I don't rail against Ferrari owners. The fact is you're like Aunt Minnie, you are too few in numbers to materially have any effect on global levels of fuel economy. It's The Big Middle that will decide how well we do on overall fuel efficiency gains and whilst not perfect, I'd say the numbers are inching in the right direction.

Whilst I'm a Greenie, I do get that some folks don't want to know. I think that whether you are or aren't is basically a reflection of how you see your connection to future generations. The 'I want to cram as much into my three score and ten and bugger the consequences' has been the default philosophy for humans since like forever. For me, it was first my kids and then my grandson that fueled my connection to what comes after I'm long dead and buried. So I go as efficiently as I can and just take what I need, rather than what I could have (like a Ferrari. It wouldn't be a big deal to go out an get one. Honest).

 

[TheKracken]

I understand minor improvements in driving habits allows for increase in mpg. My lifetime average in my insight is 64.2 mpg (it has a lifetime monitor). But for those of use who already try to gain max mpg via driving there is still room for improvement. Ie: oil aerodynamic mods, ect. Also thinner oil nets horsepower gains as well. So the 134 HP that my Gen 3 prius gets could be getting 135-137 hp with thinner oil (1%+ increase in HP).

 

[fdcg27]

Efficiency is its own reward. What you don't spend on fuel to drive, to heat and cool your house and to light it is money that stays in your pocket.
Not too many people here seem to get this.
I am a fan of minimalist cars and find your little Suzi intriguing. It must be a three cylinder turbo, no?
We too venture about an hour and a half to see our wee grandson regularly, although our 30 mpg (US) Accord probably costs us less to drive than your little guy given the cheap price of fuel here relative to the UK.
It is truly wise to leave behind as much of the planet's resources as we can for future generations.
To consume as much as we can merely because it's cheap is childish.
It's also wise to limit the environmental impact of our way of living in an effort to preserve the planet for future generations.
To do otherwise is no more than selfish.
I think of my sons and my first grandchild and I would like to have them live as well as I and my wife have long after I am gone, as well as generations to come.

 

[CR94]

Originally Posted By: TheKracken
... Also thinner oil nets horsepower gains as well. So the 134 HP that my Gen 3 prius gets could be getting 135-137 hp with thinner oil (1%+ increase in HP).
Except that your engine (alone) claims only 98 Hp [73 Kw], with "thinner oil" already factored in.

 

[Shannow]

Originally Posted By: CR94
Originally Posted By: TheKracken
... Also thinner oil nets horsepower gains as well. So the 134 HP that my Gen 3 prius gets could be getting 135-137 hp with thinner oil (1%+ increase in HP).
Except that your engine (alone) claims only 98 Hp [73 Kw], with "thinner oil" already factored in.


Not a bad point there...then there's the 1% claim...

another good selby paper for the discussion.

http://tannasco.com/images/FEI_TAE_2012_01.PDF

 

[BrocLuno]

Efficiency can be looked at many ways. Racers are all about efficiency per unit of given displacement. The more efficient team and motor set-up usually wins (baring accidents from outside influences...). But I don't think anyone in this discussion would count racers as good for mankind or overall hydrocarbon usage ...

What really bakes my cookies is the shots of oil fields around the world flaring off gasses while we try to eek out a few % savings on home heating. I just rankles me so, that I want to go out and boil the tires in a practice "leave" or something ...

That's thousands of tons of CO2 and direct heat going into the atmosphere every second and no one seems to want to talk about it ...

Run better tires and add 1 PSI and you'll do more than all this oil talk

 

[09_GXP]

Originally Posted By: Jetronic
Originally Posted By: 09_GXP
Originally Posted By: IndyIan

Oil temps also vary alot with engine rpm and not so much load, and I assume a prius runs pretty low rpms in normal driving.


This may be true for some engines, such as the Prius here, but will vary greatly with engine design and is not a good rule of thumb. For example, engines that have piston cooling nozzles will see the oil pan temp track very closely to fuel usage or exhaust gas temps.


All the engines I've had with piston cooling nozzles still had the RPM and oil temp in sync.


I'll agree there is a link between RPM and oil temp. But from what I have seen on every engine I've had in a test cell is that the link is very minor compared to the relationship that exists between oil temp and fueling with PCNs are involved.

 

[TheKracken]

Even if I don't end up experimenting with thinner oils for efficiency it is still fun to know the science about it. And thank you to the poster for correcting the HP output of my engine, forgot they already include the electric motors HP output as well.

 

[Jetronic]

Originally Posted By: 09_GXP
Originally Posted By: Jetronic
Originally Posted By: 09_GXP
Originally Posted By: IndyIan

Oil temps also vary alot with engine rpm and not so much load, and I assume a prius runs pretty low rpms in normal driving.


This may be true for some engines, such as the Prius here, but will vary greatly with engine design and is not a good rule of thumb. For example, engines that have piston cooling nozzles will see the oil pan temp track very closely to fuel usage or exhaust gas temps.


All the engines I've had with piston cooling nozzles still had the RPM and oil temp in sync.


I'll agree there is a link between RPM and oil temp. But from what I have seen on every engine I've had in a test cell is that the link is very minor compared to the relationship that exists between oil temp and fueling with PCNs are involved.


In practice, load and RPM go up both together, as it's only high speed runs that really elevate oil temps from the thermostat controlled 80°C I'd see while cruising.

 

[Shannow]

Thermal load into the oil is predominantly RPM based.

As demonstrated in my Caprice, if I spend 10 minutes at 100km/h in "D" at 1,700RPM, a type K thermocouple down the dipstick reads 95C.

Pull exactly the same trip at exactly the same speed in "2" at 4,000RPM+, and it will read 130-135C.

SAme road load, more frictional loss in the engine, more oil temperature.

Couple of different ways of looking at it from research papers.

First influence of RPM and engine load on engine oil wramup...

two points in an engine at different rpm..

Note the heat generation IN the bearings and flowing into the rods and block...

Big end bearing temps...note that load is way less influence than speed...

 

[steve20]

incredible amount of detailed info----could never find this anywhere else but here--!
Thanks Guys
Steve

 

[TheKracken]

So, one thing I am still unsure of since Fuel economy is not based on the numbers I posted. Would a 5w20 or a 0w40 be better for fuel economy at start up? Which would be thinner?