Amazing

How much mpg can be had by staying out of the throttle.

Yesterday, my SO and me took a leisurely 80 mile drive around the lake. Much of it was cruising at 50 mph on the shore road. My Fiesta showed 44 mpg on the trip computer.

Then again, At the Keene NY hill climb reunion, driving spiritedly up the mountain shows about 10 mpg.

Trip computers aren't real life.

Calculate miles driven since fillup divided by fuel replaced.

In reply to Ricky Spanish:

Every single time I have done a proper calculation on my fuel economy for my 2008 Duramax I have found the trip computer to be dead on.

"Real life" calculations seem like a waste of time if the trip computer is accurate and already giving me the correct information.

I have long thought the trip computer is way more accurate than the fill and calculate method. ECUs need to know exactly how much fuel is going into an engine, much science and engineering goes into measuring fuel flow through an injector.

Gas stations on the other hand don't really care if they don't fill your tank to the exact same line every time. How does the pump know when to shutoff? How recently was the pump meter inspected by the state? How well paid off was the state meter inspector? How hot was it outside when you filled up? How hot was the existing gas in your tank when you filled up? How hot was the gas in the tank underneath the station?

Eliminate the variables you cannot control (and often have misaligned interests) and work with the one that has aligned interests.

Most modern trip computers tend to be within 5% of "real life" calculations now a days.

Granted its usually on the optimistic side but still its close.

At least for GM, I've found the MPG calculations accurate enough, after checking my first dozen tanks manually, that I now take the computer at it's word.

On last summer's road trip, I filled my Sonic halfway up the Eisenhower Pass, so most of the tank was going downhill to Denver. Got 47mpg on that tank! Normal highway driving nets about 37, so that was a fun win!

Yeah, my fuel computer is always within a tenth of what I calculate so I've given up doing it the hard way.

EvanR wrote: On last summer's road trip, I filled my Sonic halfway up the Eisenhower Pass, so most of the tank was going downhill to Denver. Got 47mpg on that tank! Normal highway driving nets about 37, so that was a fun win!

Tank after tank we're averaging 35 with ours, and neither of us take it easy. During one leisurely drive when the freeway was closed and we had to take the scenic route it went all the way up to 41. It's pretty good.

There was about 1 mpg difference the one time I checked.

Close enough.

OH,OH, I made a mistake. Instead of 44 it was 47.

Yeah, that seems to be a common sentiment that trip computers are not accurate and cannot be trusted because they overstate mileage, but I haven't found that to be the case in the two cars that I've checked on. If the ECU doesn't know how much gas got squirted through the injectors or how many miles I've driven, then something is seriously wrong. I believe this to be an old wives tale or maybe something based on decades old information.

I took a road trip a couple years ago in the WRX (about 500 miles), the car is tuned to 280whp and my "normal commute" mpg is 23.5 almost on the nose for the last 150k miles.

Anyhow, on that road trip I used my boost gauge to stay out of boost, kept my speed under 62mph on the highway (the sweet spot for this car), and didn't pass, accelerate aggressively. Trip computer (which has been nearly dead-on for the car's lifespan compared to my actual fuel/mileage logs) registered somewhere in the neighborhood of 34mpg on an AWD, turbo car.

Typically on highway road trips driving like I usually drive I can pull about 29mpg if there's no city driving.

So, 34mpg in a WRX is pretty impressive....but man, that was one boring trip just to satisfy my curiosity....

unrelated, at STPR rally we did 259.4 combined stage and transit miles in the rally car (1985 BMW 318i with 1991 M42 engine) and only went through 12.5 gallons of fuel. 20.5mpg with more than half of that basically being at wide-open, and doing a lot of uphill. That car will pull 30+mpg all day long while towing the little tire trailer to rallycrosses and easily 35 if just cruising not loaded up with gear...

So in that comparison, a car with a 26-year old engine that weighs a bit less than a Fiesta only gets about 8mpg worse.....which makes modern cars sound less impressive lol....

No matter if you're calculating manually or trusting the computer you'll be off by however much the speedometer/odometer is, usually a few percent fast.

My last 2 e46 trip computers were at least 1, if not 2 MPG off from true mileage.

BrokenYugo wrote: No matter if you're calculating manually or trusting the computer you'll be off by however much the speedometer/odometer is, usually a few percent fast.

Yeah, but who doesn't calculate their odometer error by paying attention to milepost signs vs. odometer readings?

You can get a good idea of a percentage over ten miles, although the longer the distance the better as any possible error in signpost placement gets less and less relevant. Although, I don't know if it's a Federal requirement thing or just something Ohio does, but here the posts are near-as-possible exactly where they are supposed to be, and if they can't put the mile/tenth marker where it needs to be, they omit it.

I've found that GPS is inaccurate because it doesn't account for hills. You're given your speed/distance over the bottom leg of the triangle, not the hypoteneuse, which is the road you're driving. At least my Garmin gets confused by hills. I bet if I went 100mph down a mineshaft it would report 0mph.

iceracer wrote: How much mpg can be had by staying out of the throttle....

I don't know, I've haven't touched the throttle in the broken down ion for over a month. Technically it's getting 0 mpg ... I'm not amazed at all either

In reply to irish44j:

Boosted cars are pretty neat if you can stay out of the throttle. My MS3 will return 33 mpg cruising on the highway if I stay out of it. That's been warmed over to about 350 HP at the wheels.

It falls off fast though if I'm aggressively picking up speed to merge on PAs oh so long on ramps.

Normal is about 26.5 mpg since I have a lot of mixed rural and highway driving.thr trip computer is almost always deadnuts on.

Of course, the instantaneous mileage readings on a dash computer aren't going to be useful, but over a long trip I've found they are pretty accurate. Using the cruise control usually helps a lot, too.

Back in the middle 1970s, my brother in law bought a new Ford F-100 with a 300ci six engine. It had an optional vacuum gauge in the dash. I borrowed it once, for a trip that was about 100 miles each direction. On the return trip, I paid attention to the vacuum gauge, and basically did the old 'drive like you have an egg between your foot and the gas pedal' technique to keep the average vacuum reading as high as I could. Speed was basically the same in both directions, but the mileage was much better on that return trip.

Addressing the mile markers, I've been tracking them since the 70s. I was a race horse trainer, so I used to use them with my stopwatch as a substitute for a broken speedometer.

I've observed that they are very precise in their placement. If they weren't, the cumulative error would be quite large.

I have not reset the average mpg on my sierra Denali for about 20k miles and it still thinks that I am averaging about 20 mpg but when the tank is full with 24 gallons of fuel it saids I will only get 354 miles out of it. The math just does not add up.

For the record the 354 on a full tank is much closer to reality.

dean1484 wrote: I have not reset the average mpg on my sierra Denali for about 20k miles and it still thinks that I am averaging about 20 mph but when the tank is full with 24 gallons of fuel it saids I will only get 354 miles out of it. The math just does not add up. For the record the 354 on a full tank is much closer to reality.

Dean, did you mean 20 mpg instead of mph?

T.J. wrote:

dean1484 wrote: I have not reset the average mpg on my sierra Denali for about 20k miles and it still thinks that I am averaging about 20 mph but when the tank is full with 24 gallons of fuel it saids I will only get 354 miles out of it. The math just does not add up. For the record the 354 on a full tank is much closer to reality.

Dean, did you mean 20 mpg instead of mph?

Yep autocorrect got me will fix it now tks!!!

Trip computer at 4800 miles since new reads 28.8. GMC app Lifetime is 29.1. Last 450 Mile Economy is 31.x. Last fill up calculation was 30.0, always same pump, same fill.

All close enough for me, nothin' to nit pick about one vs another considering tire pressure, winter/ summer fuel and regens.

Only use the Last 50 Mile Economy to tune my throttle foot, it's almost like a game to beat your high score.

Being aware of real-time fuel economy is helpful. Installing a ScanGauge II in the Protege improved its mileage by about 1.5 mpg. I'm working on a better mount for the one in the Miata, and my last three tanks (since I took out the ScanGauge) have been down by about 2 mpg. I need to get one for the P71. Haven't broken 18 in it yet.

My wrx gets 22 no matter what. If i drive like a 36 year old dad with my kids in the car i get 22. If i drive like i'm 18 again i get 22. 99% of the time though it's dad mode.

The cummins ram though, if i am nice to it i can get it up to 23 for all highway trips without trailer or with empty open trailer. If you drive like a bro your fuel mileage dies a whirring boosted death in an engine that huge.

irish44j wrote: So in that comparison, a car with a 26-year old engine that weighs a bit less than a Fiesta only gets about 8mpg worse.....which makes modern cars sound less impressive lol....

8mpg is over 20% better.. that's an enormous increase.