Accurate MPG calculations

[Rarasranger]

I'd like to get a comparo from ya'll as far as gas mileage.

The last 3 tanks of gas have been between 29-33 MPG with a 1992 3.0 ext cab-manual-3.55 gear-2 wheel drive- 24.5 inch street tires.

I've been running back and forth from LA to San Diego once a week lately and I wanted to get some good consistent numbers so I've been writing down everything. I'm really impressed with this little truck. I admit though that no one wants to be behind me cause I do drive slow! 65mph usually and I take my time gettin up to speed.

Oh. I've been reading on the boards that shifting at 3000 is good but I've been shifting at 2500rpms for this test period.

How bout you guys?

 

[MAKG]

You're getting 30 MPG and complaining?

You'll never do better than that with a truck.

You have smaller than stock tires. Make sure your speedometer is compensated. Or your mileage isn't as good as you think it is. And you really are driving like a granny (closer to 55 MPH than 65).

 

[philS]

87 Ranger 2WD 2.9 5-speed 110K Short Cab Long Bed stock tires 3.45 rear: 25 mpg

I do 65 mph tops on the highway

Going from 65 to 75 will cost you 4-5 mpg

 

[MrE_Powers]

3000 is your engines peak tourque range so shifting 3500-3800 would be better for fuel economy

2500-3000 is where your engine is hitting your stride. also consider what you have in your bed.

i was getting 21mpg highway in my 93 till i got a tool box and now i get about 19 mpg. and i also do 60-65

i think if you want the best results get a cloth tounnel cover and not a hard one or drive with no tailgate at all but if you need it keep tail gate up.

you might want to get speedo checked out because every year ranger i checked out at Fueleconomy.gov that has the 3.0 vulcan engine got between21-23 mpg for fuel economy with the ffvs pulling in at 18mpg for regular gas and 15mpg e85

 

[Rarasranger]

You're getting 30 MPG and complaining?

You'll never do better than that with a truck.

You have smaller than stock tires. Make sure your speedometer is compensated. Or your mileage isn't as good as you think it is. And you really are driving like a granny (closer to 55 MPH than 65).

Oh no. I'm not complaining a bit. I'm very happy with this truck. That mileage and speed is taken from GPS and backed up by my wife running the same route in her car right in front of me.

As an aside, you'll very rarely if ever hear me complain about things. I figure there's always another way to fix or achieve something, I'm just too dense to figure it all out sometimes. I also knew people would be skeptical when I put this post up but it's the truth and I've checked my record keeping and calculations several times.

 

[tbirdsps]

I'm getting a consistant 22 around town and 26 highway with my 92 2.3 will 99,000 miles.

 

[rboyer]

Your GPS readings may not be too accurate. If you have a lower end GPS receiver you could have an inaccuracy of 3 meters or maybe even more at times. The most accurate way of calculating fuel mileage would be with a Differential GPS unit which only has a rated inaccuracy of 0.67 m per 100 km. Now a few meters here and there don't sound like a lot, but think of it over the course of a full tank of gas. It could be throwing you off by 2 or 3 mpg at times with an older style unit.

 

[Rarasranger]

Your GPS readings may not be too accurate. If you have a lower end GPS receiver you could have an inaccuracy of 3 meters or maybe even more at times. The most accurate way of calculating fuel mileage would be with a Differential GPS unit which only has a rated inaccuracy of 0.67 m per 100 km. Now a few meters here and there don't sound like a lot, but think of it over the course of a full tank of gas. It could be throwing you off by 2 or 3 mpg at times with an older style unit.

I hear you. Thats why I also factored in the other car's speedo and mileage as a control. Either way, I'm really enjoying this truck... Except for the coolant leak at the block, (sigh). Pulling the engine to change oil pan gasket (another small issue)... I've considered just sliding in a rebuilt 3.0 instead. (Tax refund!)

 

[HareRazor]

In my 91 2wd standard cab 3.0 Ranger I am lucky to get 20 mpg. The most I have ever gotten was 24 mpg driving with the wind pushing me.

 

[rboyer]

It all comes down to this: Are you getting what you want out of it compared to the gas mileage you get? When I bought my Ranger I knew it wasn't going to get more than 18mpg especially with 33 inch tires on it, but the thing looked so nice and I got it so cheap that I didn't really care about gas mileage at the time. I went out and bought a Subaru legacy Outback to compensate for the whole mileage thing. When i'm going on a long drive I just take the car and if I need to haul something I either stick it in the back or hook up the trailer if it's something too big to fit inside the car. But if I need a truck for something or just want to go play around at the strippins I take the Ranger. When it all comes down to it, it depends on your specific application for the truck. Now if you really are getting around 30mpg then that's pretty damn good because that's what I get on average with my little 4cyl subaru.

 

[Rarasranger]

I'll be leaving late tonight (after rush hour) to do the same 420 mile round trip. I promise to the God's of Engineers that I'll double check everything I calculate and I promise to ya'll that I won't lie in my results! LOL!

 

[Will]

3 meters accuracy would be outstanding. All of those position plots are going to land in a 10' circle around you. Most will hit your truck. It's not going to cumulate into a huge error.

 

[MAKG]

Will, error in velocity is much larger than that.

The distinction is that you are taking the difference between two closely spaced measurements to get the velocity. How closely spaced? Depends on how the GPS implements it. Make the spacing much closer than 3 meters, and it's easy to see that the velocity can be just about anything, including pointing exactly backwards, with alarmingly high probability. Make the timestep too long and it doesn't see variation, such as curves, and will underpredict speeds around curves, worse as it gets sharper.

Measuring a rate-of-change accurately is a black art. It's not as simple as saying "I have 3 meters. Great." Smaller is better, to a point.

As an example, a Magellan 215 I keep around can't measure speeds below 2 MPH -- it just jumps to zero with an obvious sampling error, and as a result gets headings badly wrong. This is a handheld; it really should be able to handle walking speeds. It CAN measure positions in good conditions to several feet. The problem is that its samples are too close to resolve.

This is a generic problem with subtractions called "loss of precision." Is it going on here? Who knows. GPS algorithms are proprietary. I do see my own more modern GPS (Garmin Nuvi 370) consistently underpredicts a measured mile by about 5%. Meaning, drive so the GPS says 60 MPH for 60 seconds, and see how far you got. And it's less than a measured mile. This can be measured with the GPS (with a little calculation), or with survey markers.

 

[Will]

I admit to ignorance. But I was thinking it would be simple for it to have software to correct itself. If it keeps checking back to earlier plots it should be able to be very accurate I would think. Chart plotters are extremely reliable--so much so that nobody know how to celestial navigate anymore except eccentric gnomish sailors.

 

[MAKG]

Oh yes, plotting position against time for a whole bunch of measurements to get a mean velocity is VERY accurate. It's only when you try to estimate what the velocity is RIGHT NOW, with no history that you (might) run into trouble.

FYI, no one navigates point to point based upon GPS velocities and headings alone. They aren't nearly accurate enough (I continually run into this problem when trying to point a telescope -- avionics gives heading to 0.5 deg accuracy; which is the broad side of a barn for telescope pointing, and it's much larger than many instruments' fields of view). What one does is modify the heading during transport to match the measured bearing at the later time, given actual conditions. You don't just aim your plane at New York and go to the back and have a beer. You continually change the heading a little bit as you get closer (this is "guidance").

I have some idea how to navigate celestially because one of my major projects is the reverse problem. Calculating true headings to fly an aircraft to keep the azimuth of a given celestial object (star, planet, or the Moon) constant. It's an airborne telescope with very little lateral motion. Not that I've ever used an astrolabe.