Preliminary gas mileage observations on the V8

[Buckfever]

Clearly this is very preliminary and I need to test the accuracy of the computer at various speeds to see if it provides relative accuracy. Which is to say that I need to check if it is off the same at higher and lower speeds. That said I did get some initial work on this using the computer. I would set the cruise contol and then reset the computer on a level portion of the highway and let it run till the deviations for slope had all but settled, so that should be close anyway.

63mph provided 19.7-19.8.
69mph provided 19.2-19.3
73-74mph provided 17.2-17.3

I'm going to test this further, but there seems to be a big drop off in MPG once we bring it up closer to 75mph.

The other thing and this one is very anecdotal at this time is that the V8 city mileage can be quite good. By ulitizing a gentle touch to the pedal, which is all you need with this engine, I was getting excellent gas mileage. Indeed we have a lot of 40-50 mile stretches here and the mixed driving including those stretches was rivaling the highway gas mileage.

Not sure where my driving habits will settle with this vehicle, but I was figuring a whole lot less, on the city driving.

Is this similar to what you guys are finding?

 

[toto]

The trip computer isn't accurate, so don't bother messing with it. (It generally reads MPG about 10% better than reality.) It's great for displaying the outdoor temperature.
You're better off tracking mileage with the trip odometer and then noting how much gas you put in when you fill it up.

The optimal gas mileage for any car will be at the speed where it shifts into overdrive. The faster you go beyond that, the worse the MPG will be because you're running at higher RPM's. That's why the national speed limit was set at 55 MPH during the oil crisis in the 1970's.

I'm getting about 15.5 city (with very short trips and a somewhat lead foot at stoplights) and 18-19 highway, so I'd say you're doing fine on MPG. Some members are posting even better numbers.

 

[charlier180]

Buckfever, the accuracy of the on board computer has been discussed at great length over the last few years. The overwhelming concensus among owners here is that the computer reads higher than the actual (ie calculated) mileage.

For me personally, the computer in my V8 4Runner is high by about 13-15%. I tend to refill my 4Runner when the tank is 3/4 empty. I have noticed that the inaccuracy of the computer is fairly constant when I fill up at 3/4. When I refill with less fuel the inaccuracy of the computer is even worse.

As far as speed and MPG I have observed that my 4Runner appears to gets it's optimal (calculated) MPG around 45-55mph on level roads.
Unfortunately, maintaining that speed is not always possible, practical or safe even when the posted speed limits are within that range.

 

[Buckfever]

I guess what I'm looking for is whether there is a speed at which the gas mileage really starts dropping off precipitously. I typically run at 73 in a 65 and my initial observations suggest in terms of fuel economy is that keeping it under 70 will provide much better fuel economy. Typically it's not linear, it starts dropping off hard at some point. Just trying to figure where that is.

 

[jeober]

Hi Buck,

Your mpg fall off is primarily windresistance which is a squared function of velocity. So mpg is very sensitive to your speed. If you could drive in top gear at 45 mph you would get remarkably good mpg. Your mpg drop off is continuous and acceleratingly worse -- 55 is better than 60, 60 is better than 65, etc. So you just have to pick your cruising speed given the mpg cost.

Our 4Runners are aerodynamic bricks but we love them in spite of it.

 

[jpalaska]

LOL,aerodynamic brick, for sure.
Does anyone here know what the drag coefficient for the 4th Gen 4Runner is?

JP

 

[greasefingers]

True, instantaneous fuel economy can help predict the obvious. Jeober hit the nail on the head. The slower you drive the better the fuel mileage

 

[biglatka]

Clearly this is very preliminary and I need to test the accuracy of the computer at various speeds to see if it provides relative accuracy. Which is to say that I need to check if it is off the same at higher and lower speeds. That said I did get some initial work on this using the computer. I would set the cruise contol and then reset the computer on a level portion of the highway and let it run till the deviations for slope had all but settled, so that should be close anyway.

63mph provided 19.7-19.8.
69mph provided 19.2-19.3
73-74mph provided 17.2-17.3

I'm going to test this further, but there seems to be a big drop off in MPG once we bring it up closer to 75mph.

The other thing and this one is very anecdotal at this time is that the V8 city mileage can be quite good. By ulitizing a gentle touch to the pedal, which is all you need with this engine, I was getting excellent gas mileage. Indeed we have a lot of 40-50 mile stretches here and the mixed driving including those stretches was rivaling the highway gas mileage.

Not sure where my driving habits will settle with this vehicle, but I was figuring a whole lot less, on the city driving.

Is this similar to what you guys are finding?

Buckfever,
As others have noted, the computer as an absolute predictor of MPG is inaccurate. I have posted previously on this forum that I found the computer to be 7% inaccurate if you reset the computer every 1-3 fill ups. Having said that, I agree with the way you are using it. If you ignore it's inaccuracy or better yet, normalize for it, it can be a very useful tool to research an analyze the effect of various driving habits/situations on fuel economy. Again, as also pointed out, the wind resistance (drag) is proportional to the square of the velocity and hence nonlinear as you have discovered. Of course there are other factors in fuel economy, the driver's mode of driving being a big one. If you drive the 4Runner with a vacuum gauge connected to the intake manifold and attempt to maximize it's reading, like driving with an egg between your foot and the accelerator, you will get the best mileage. But that takes a lot of the fun out of owning a 4Runner. There seems to be a sweet spot of about 100 km/h (62.5 m/h) where you get the best compromise between speed and gas mileage, as your data obviously shows.

Thanks for posting your findings, my data matches yours very closely. Please post anything else you find out. The best I have attained with my 4Runner has been 20.2 mpg under ideal conditions, with cruise on, averaging in the low 60's (mph). The worst mileage has been in the low 14's in city/suburban stop and go driving. I don

 

[RickyCRX]

All of these are calculated based on miles driven divided by gallons pumped. I always top off to the filler neck for consistency:

Best mileage: 20.9mpg.

Worst: somewhere around 7.0mpg (pulling a massive enclosed trailer)

Ricky

 

[Uneek]

LOL,aerodynamic brick, for sure.
Does anyone here know what the drag coefficient for the 4th Gen 4Runner is?

JP

4Runner is 0.398. I find it hard to believe the FJC is better at 0.397. Insignificant though, must be that more curved windshield.

Source

 

[Uneek]

I've noticed anything above 70mph the hit on gas mileage is pretty big, as much as 3 mpg. I haven't driven at 60mph to test for gas mileage, feels like I'm holding up traffic with cars flying by and it's too easy to go 80mph in the 4Runner and not feel it.

 

[sharp4runr]

4Runner is 0.398. I find it hard to believe the FJC is better at 0.397. Insignificant though, must be that more curved windshield.

Source

Hey thanks for posting that info. I learned something new today

 

[Buckfever]

I played with it some more today. Clearly 73-74mph drops it right down to the 17mpg range. 59mph is real good up over 21, but who want's to drive that slow? Besides it mostly isn't safe to do so.

I'll probably just as a rule of thumb keep it just under 70. The city mpg is what was most suprising to me. I was expecting 12 at best, seems to be doing much better.

On the next fill up, I'll check what I get via mixed driving and compare that to the computer.

 

[Light_Mania]

4Runner is 0.398. I find it hard to believe the FJC is better at 0.397. Insignificant though, must be that more curved windshield.

Source

Don't forget that coefficient of drag is only one part of the wind resistance equation. You also have to multiply Cd by the vehicle's frontal area to get an idea of how hard it is to push it through the air.

 

[jonhul]

I'm finding my computer to be about 1.5% on the high side or about .3-.4 mpg high. I did a round trip to Dallas, 403 miles, and had an actual 20.1 mph. The computer read 20.3 mpg. This was with the cruise locked on 72 on the interstate. In town I average 17.8 and the computer reads 18.1. I can say that I'm extremely pleased with the mileage, especially since it's a v8. It's been a pleasant surprise- in addition to the low insurance rates. I also have a 94 Land Cruiser, v6 that gets 14.5 in town and 17 on the hiway. The liability only insurance on the cruiser costs the same as full coverage on the 06 4R. Explain that one.

 

[06_Limited]

My trip computer is about 3% high...

My 4Runner is getting 16.8 mpg overall, which is great. My previous Jeep Grand Cherokee 4.7L averaged 13.8 mpg, and the Toyota has more power...

No complaints here.

 

[biglatka]

Don't forget that coefficient of drag is only one part of the wind resistance equation. You also have to multiply Cd by the vehicle's frontal area to get an idea of how hard it is to push it through the air.

You're right, here's the entire formula:

Effect of air resistance on car moving at increasing velocity

Fair =

 

[Falls]

I know I'm probably going to get crap about it but I find the on board comp. to be accurate , in all aspects.

I've check it multiple times and it has been close enough for me to call it accurate.

I've done multiple tests where driving on flat surface hiway and setting the cruise at 60 , then resetting the avg. mph on the comp. I went on a flat hiway , nice clear day , no wind and the comp. read like 60 the complete time. ( approx 25 min) . I did the same thing on the way back with the same results. I've done this because of everyone saying how in accurate it is , it useless , ect,ect....

Today as a matter of fact I check my milage against my trip/odometer. We were out snow wheeling , I went through about 1/2 tank of gas today. Had alot of fun , alot of stop & go , alot of heavy foot , a little time in 4lo also. I filled up after and checked miles traveled against gallons put in . It came out to 15.5 (Its great for what we were doing today , the 4R got pretty pounded). I then check the avg. mpg and it was at 15.5 . I also reset that after my fill up.

I've never tested the range setting , but really have no need to.

I'm not saying the comp. is exact , but effective and close enough for me to trust. I've done the above tests multiple time with the same results.

Just like some called BS about the window sticker rating EPA. I've easily got what they predicted on the sticker and then some by a mpg or 2.

I think the V8 is an awesome engine and I wouldn't trade it for nothing. In a full time 4x4 V8 the milage kicks butt IMO.

By the way , had a fricken blast in the snow.

Let the flaming begin........ lol

 

[jpalaska]

No flames here, Fall, just more snow.

I agree with you. My ECU estimate of my mpg has been pretty damn close to what I've calculated at fill ups.

Both report around 16.5, and that's been all city driving so far.

And I've got almost 800 miles on my 4Runner. I'm looking forward to knocking down that mpg a bit after break in, by letting my 2UZ-FE VVT-i show me what she's really got.

VAROOM, Baby!!!

JP

 

[greasefingers]

06_Limited,
Now that