MPGs - Many People Griping - A Foundational Knowledge Primer To Assist in Better Efficiency

[TakaraLC]

I think this is a great explanation of how it conceptually works, with the only thing I’d add being that modern turbo engines and the ECUs managing them, tend to do a really good job of fully overcoming elevation related losses until you climb pretty high. What I mean is that the variation between atmospheric pressure at sea level and say 5000 ft can easily be overcome by the turbos spinning up and cramming in more thin air until air volume and pressure reach the desired thresholds up to the point where the system limits (primarily turbine size, turbo RPMs and heat management) mandate it to back off and stop compensating.

What weighs more: a pound of sea level dense air or a pound of thin air at 5k ft? SAME, just requires a bit more of the latter to achieve a pound. At some level of elevation, the thin-ness of the air just becomes such that the turbo can no longer spin fast enough to fully provide the compensating compression and volume due to heat and friction so you experience power loss but I certainly think at elevations up to at least 5000-7500 ft, there probably isn’t any loss at all for newer forced induction motors which cannot be said of naturally aspirated counterparts.

Yeah most modern turbos are (designed to be) limited by output pressure, meaning the how fast the turbo spins is restricted by the internal air resistance on the turbine. At altitude, the turbo will be still reach to the same output pressure (boost), but the turbine will spin to a faster RPM to do it since input air density is lower and therefore generates less internal resistance.

I am sure after a certain altitude, mechanical resistance inside the turbo becomes limiting so the turbine cannot spin any faster even if input pressure decreases, but that is probably above 15k feet range.

 

[TakaraLC]

My apologies I misunderstood the original post. You are correct I was focusing on a different aspect. For the larger media screens. If you go to menu and then go to the car. Does it give you the option to see that there? The 1958 is limited to just three options. Hopefully the higher trim would allow you to see this as an active log while driving.

No unfortunately there isn’t. I think we the option to display more at the same time on larger instrument cluster, but the available gauges are the same. On media screen, there is the option to plot gas mileage, but nothing about regen or hybrid system.

 

[New York Ralph]

There is a lot of conversation around the small gas tank and bad gas mileage (and correspondingly low overall range) for the LC250 so I figured it might be useful to address some of the basics around how the forced induction impacts fuel consumption so people can adjust their expectations and behaviors.

"Well anybody who can afford this car, shouldn't care about gas mileage because they can afford the gas!" - Well I most definitely can afford the gas, and premium at that, but being very far off of advertised EPA estimates is worthy of being upsetting even if one can afford to pay for gas and expensive gas even.

"The hybrid system in the LC250 isn't designed for fuel efficiency, but for low end power, so get over it". - Well yes, it's not BIASED toward the explicit goal of extracting maximum fuel efficiency, but by definition, the electric boost results in recaptured energy otherwise wasted and dissipated as heat via the brakes, and instead adds torque and power to the wheels, which necessarily translates to forward motion that otherwise wouldn't exist in the absence of the hybrid system. So either way, it generates more power and forward motion vs a non-hybrid system, even if its BIAS is more for supplementing power or filling holes in the power band while the turbo spools, etc.

"Toyota is silly, their ECO mode isn't actually better for MPGs, put it in Normal or Sport mode". - I love how people extoll the virtues of Toyota engineering and how they are very intentional with design and then decide that they actually programmed ECO mode to be less economical than Normal or Sport because they don't like the slower responses and compensate by being heavy footed during ECO mode and end up keeping the motor in boost a lot and wonder why ECO isn't getting them better mileage. You can't counteract ECO by being lead footed to offset slightly slower responses and acceleration, it's self defeating.

Without splitting hairs too finely and getting down to stoichiometric specifics regarding rich vs lean air fuel ratios run on the T24A - FTS, one can use the engine displacement (2.4L), compression ratio (11.0:1) and various boost pressures of the turbo, to get some understanding of back of the envelope naturally aspirated equivalent for various boost pressures from the turbo. After all, engines and the way they generate power is all just a giant pump of air and fuel. Think of the turbo as displacement on demand. So here we go:

1) No boost - 2.4L engine
2) 10 PSI boost - 4.03L engine
3) 15 PSI boost - 4.85L engine
4) 20 PSI boost - 6.07L engine

So if you're easy on the pedal and more importantly in ECO mode and driving smoothly (vs abruptly accelerating and winding up the turbo boost pressures), it consumes the fuel equivalent of the above stated naturally aspirated engines at the various loads described. If you're constantly at 10 PSI of boost, you're roughly ingesting and burning up the air/fuel of a 4L engine for those moments. The car is too heavy and big to be operating as solely a 2.4L 4 cylinder, for lots of the time, but to be under low single digits of boost for periods vs 10+ lbs makes quite a difference for fuel economy. I never hesitate to call on its full power when I need to accelerate quickly, I am merely pointing this out to the countless people who are confused as to why their fuel economy is low when they wind up the motor quite often and spend a lot of time in boost. Separately, the hybrid electric assist can also be thought of as additional displacement equivalent roughly equating to ~0.8L across the entire range. so factor that in as well (but this doesn't cost us any additional fuel, so is really quite a neat perk). Now add that back in and suddenly being a 2.4L supplemented by a 0.8L of equivalent electric power sounds a lot more reasonable at 3.2L displacement equivalent.

Fuelly shows an average of ~19 MPGs mixed for the LC250 and I think between this forum and that site, there is selection bias for LC/car enthusiasts that have a penchant for modifying their cars and in the case of the LC, typically upsizing their wheels and tires and lifting them, adding armor etc, which reduces MPGs. With stock suspension and tires, the LC has no issues being able to reach its EPA ratings if driven reasonably, and without calling on its full power potential constantly.

Good information. I have been getting 22.8 overall since last year with stock 20" rims and tires.

 

[ultane]

After a while when you own a vehicle, you get to know pretty closely how much additional fuel you can add after the initial pump shutdown to within a few tenths. That will get you within a few tenths in your calculations....consistently. It seems the fuel tank is on the left of LC. That would also suggest you would get slightly more in the tank if right side is higher. Would be pretty interesting if anyone has run the tank dry and done a complete fillup.

The Car Care Nut (YouTube) recommends to NOT add additional fuel after the pump shuts off, as it will eventually fill the charcoal canister. They are not cheap, and likewise not easy to replace. DAMHIKT….

I have run for ~30 miles after the DTE showed 0. I put 16.5 gallons of fuel back in the tank.


Edited: To state proper amount of fuel on FIRST fill up on day one of ownership (I keep receipts).

 

[teghogh]

The Car and Driver test flat out says they hold the car at 75 MPH… the fuel consumption at that speed will not be all that different between GX and LC for all the reasons stated previously. The small LC motor can just employ enough boost to deliver the power of a much larger motor like the GX’s. Drop down to 70 or 65 MPH and the fuel consumption between LC and GX at those highway speeds is drastically different. As I said, think of the turbo and hybrid as displacement on demand. The neat party trick however cannot be done in reverse by the GX where it sheds displacement (and pistons) to be anywhere near as efficient as the LC motor because at its baseline, it’s a much larger motor even when driven gingerly. I love that the LC can step up and power the car to near GX levels of HP and Torque for bursts as needed, but then is much more gas efficient the rest of the time. That’s a really nice feature and attribute to possess. The GX engine is way more thirsty for the rest of the time. I also love that the LC achieves that big power not solely through employing more boost, but also incorporating hybrid electric boost so as to not stress the engine as much as would be the case if it went to max boost pressures of say 20-25 without electric vs the 10-15 with electric it runs at.

Took the stock gx OT on the freeway for a 40 mile loop. Going 65mph , 29.7 on the way there and 22 coming back . That’s 26mpg combined. As for city driving on I’m getting 2 mpg less compared to stock lc

 

[Sugarloafer80]

Stellantis is still playing catchup in hybrid world. I had a Tonale loaner for a week a year ago. I believe same fundamental type of system. Loved it. Loved how you could do 75mph pure EV mode. Only had ~32? miles of range but....but I did notice even coasting down my long hills etc did little to move the bar on that EV range. Fiat is totaly different..pure EV

The Car Care Nut (YouTube) recommends to NOT add additional fuel after the pump shuts off, as it will eventually fill the charcoal canister. They are not cheap, and likewise not easy to replace. DAMHIKT….

I have run for 40 miles after the DTE showed 0. I put 17.1 gallons (IIRC) of fuel back in the tank.

Yup, 2+ gallon reserve or 10 liters. I hadn't heard that one in years. Low placement of the charcoal canister was usually the culprit. I have cars that shutoff as much as 1.5 gal before I reduce flow and let it fill till it shuts off again. This is not even a full to the brim scenario. RR would only take .1-.2 after shutoff Stelvio is opposite and esp my baffled tank Evora takes forever to top up and even that is never a full to brim scenario because the tanks are vertical.

 

[TakaraLC]

Took the stock gx OT on the freeway for a 40 mile loop. Going 65mph , 29.7 on the way there and 22 coming back . That’s 26mpg combined. As for city driving on I’m getting 2 mpg less compared to stock lc

That is not combined 26 by the way.

 

[ultane]

I drove my GF to a miniature donkey show in Shelbyville, Tn. Miss Daisy got 24.2 MPG calculated at the pump for the trip over, which included two days of driving around town for meals, to and from the motel from the arena, etc.

Didn’t think that I had enough gasoline in the tank to get us home, so I used the Pure-Gas app, and found a station very near a lake (one the best chances of finding E0) just outside of Shelbyville that had 93 octane Chevron E0 fuel. Filled up there, and drove straight home, two lane highways (45-55 mph) to the interstate, then 60 mph (with some stop and go traffic) on cruise control (with traffic jam assist) until we had to get off onto a two lane highway to get home. We stopped at a rest area for pee break on the interstate, but left MIss Daisy running as we took turns going into the restrooms, then stopped at the BP station that we use locally when we got back into town, and filled up again with 93 octane E0.

Fuel economy, pump to pump, using 5.739 gallons of 93 octane E0, calculated at 29.44 MPG!!! The trip computer said we got 27.7 MPG… (picture before the one above with 12931 miles on the odometer).

Miss Daisy did good today!!!

 

[Blue Sky]

Considering this thread is dedicated to the fuel efficiency of our LCs. I would be interested in the mpg data coming from the 6th gen 4rnr I-force max operating a full-time drive.
I’m wondering if the 2 year lag on the roll-out has yielded any interesting improvements?