Gas mileage improvements..

[Serious Johnson]

Following up on some points above:

The vacuum guage/egg thing works OK-ish for a big 'Murican boat with a V8 & slushbox, but who drives those anymore ? For a fuel-injected 4-cylinder car with a manual transmission, it's most efficient to get up to speed quickly, using large throttle openings (but not quite full-throttle, which imposes open-loop mode), and shifting at very low revs. Less pumping loss from an open throttle is more efficient. That's a diesel's main advantage. Get the heck out of those lower gears as soon as possible and, above all, waste no revs!

Warm-up can only hurt -- you're getting zero MPG during that time, and causing the motor to come up to temperature much more slowly. Just start it up and drive off immeiately but, as said, gently.

Aerodynamics & other drag are certainly important. I've noticed that, in flat country, I get about the same fuel mileage when towing an empty car hauler as when there's another 5,000 lb aboard. A Wag or narrow Cherokee are not all that horribly shaped, particularly with the small stock mirrors & no roof rack. Some modern SUVs are worse -- I'm thinking of that one named for a blow-job.

In certain cases, for instance, a stock wag with a slushbox tranny & 2.72 gears, slowing down below typical highway speed doesn't help. I've seen such a rig, in perfect condition, get slightly worse economy at 50 MPH than at 75. I blame poor low-rpm efficiency in the non-lockup torque converter.

My Wag, modified with a hotrod 360, fuel injection, manual tranny, 3.73 gears, dual limited-slips, 33" tires, & 4" lift gets about 20 MPG in the mountains if I drive like I have some sense. It could do only a little better than half that when it was stock.

S.J.

[janie]

Leave the tailgate down. Every lil bit helps.

[drlocke]

Leave the tailgate down. Every lil bit helps.

I have that tailgate delete option on my I-bird pickup.

[JeeperJay]

Adding an electric fan should help a little bit....right?

That is my next planned modification. Get rid of the giant mechanical fan and install an electric one. Oh yeah, and downsizing back to 31" tires. D'oh!

[pb]

Weight = crappy mileage for stop and go driving
Aerodynamics & drivetrain = crappy mileage on highway

The heavier the object, the harder it is to start moving from rest. That's why newer aerodynamic SUV's the same weight as ours get the similiar city mileage. Not going fast enough for aerodynamics to make a great impact on mileage in city driving or for overdrive to kick in.

Aredynamics and drivetrain are important at steady speeds. An object in motion tends to stay in motion until an outside force acts upon it (air resistance & gravity) SJ described this when talking about towing. It takes less energy to keep the mass in motion than it is in getting it to that speed, not getting into the momentum/weight aspects. The more efficient the drivetrain, less energy is expended in overcoming the outside forces and remaining in motion. This is why you can get better mileage with a diesel, efi and/or overdrive in a nonaerodymanic FSJ at highway speeds as compared to stock components.

As far as improving mileage, lighten the weight and increase the drivetrain efficiency as previously mentioned.

[IslanderOffRoad]

Luckily for me, my Jeep is a hybrid- it burns gasoline, oil, and just about any other fluid you can think of!

Now if only it could burn rubber.

[drlocke]

Luckily for me, my Jeep is a hybrid- it burns gasoline, oil, and just about any other fluid you can think of!

Now if only it could burn rubber.

Try placing a spark plug wire boot on the exhaust manifold.

[710 Burner]

I can't drive with my tailgate down. I'll choke on the fumes.

[Steelhead]

Janie-
I saw a Mythbusters that busted the tailgate thing for trucks. Turns out the tailgate up creates an air-cushion that actually decreases resistance and improves mileage over tailgate down.

[IslanderOffRoad]

Try placing a spark plug wire boot on the exhaust manifold.

flamethrowers are fun!

[Tonka J200]

Leave the tailgate down. Every lil bit helps.

Sorry, Janie, I used to think the same thing, but then I found this:

"Gas Mileage and Pickup Tailgates

Tailgate up or down? The television show Mythbusters is sometimes interesting, sometimes silly but I caught one yesterday addressing this ?what everyone knows? advice.
The often repeated premise is that an open pickup truck bed is bad for gas mileage because it catches the air and creates drag, so the easy, zero cost method for increasing mileage by reducing drag is to drive with the tailgate down thereby letting the air escape. Seems logical, right?
The two hosts drove two Ford F150s, as identical as possible, filled up with identical amounts of gas, one tailgate up, one down, until they ran out of gas. Driving one behind the other, you guessed it, tailgate down went dry first! The tailgate up truck went 30 miles further. Hmm ?
Searching for an explanation they built a fluid flow simulation of a wind tunnel with a model truck. The answer lies in the fact that an open bed with a closed tailgate creates a rotating bubble of air in the bed that remains trapped there. Air coming over the top of the cab is kept out of the bed by this bubble and drops down behind the truck. Open the tailgate, the bubble disappears and air over the cab drops down faster, hitting the bed and creating drag. This explanation agrees with designers from the auto manufacturers who say the same thing. Who knew? They didn?t address the bed cover or no bed cover question which I presume will be coming up next season. "

[Russianwolf]

I just did a little research and now can say with certainty that for $10k you can have a Jeep that will never have to stop at a gas station again.

Convert the thing to EV.

One charge will get you about 70 miles. The motor is rated for vehicles up to a 5000lb GVW. If I had $10k I might try it to see how it works out.

[Don S]

Sorry, Janie, I used to think the same thing, but then I found this:

"Gas Mileage and Pickup Tailgates

Tailgate up or down? The television show Mythbusters is sometimes interesting, sometimes silly Driving one behind the other, you guessed it, tailgate down went dry first! The tailgate up truck went 30 miles further. Hmm ?
Searching for an explanation they built a fluid flow simulation of a wind tunnel with a model truck. The answer lies in the fact that an open bed with a closed tailgate creates a rotating bubble of air in the bed that remains trapped there. Air coming over the top of the cab is kept out of the bed by this bubble and drops down behind the truck. Open the tailgate, the bubble disappears and air over the cab drops down faster, hitting the bed and creating drag. This explanation agrees with designers from the auto manufacturers who say the same thing. Who knew? They didn?t address the bed cover or no bed cover question which I presume will be coming up next season. "

..
Dear Mythbusters;

... No two vehicles are going to run (consume fuel) exactly alike.
... No two drivers are going to have the same style.
... Was more air trapped in the fuel tank of one?
... Was one vehicle benefiting from drafting?
... What kind of designers? I am a designer.
hummmmmmmmm...
... In flow tests air compresses and decompresses as it flows around objects. Liquids are virtually uncompressible. Hot air from under the hood as well as hot exhaust gasses are expanding behind the real trucks will have a small effect on the air flow at the rear.
... NASCAR uses real wind tunnels to test rear spoilers for Drag (slows the vehicle and eats fuel) and down force.
I doubt the tailgate plays a large roll in fuel mileage. I have a camper shell on my Frontier and get above average fuel mileage.

Have a good one and CUL.. Don S..

[joe]

Oh so sweet!

[JPSwapMohn]

IslanderOffroad, You should get really good gas milage after mounting your GW on a Samari frame! My wife got a real kick out your Avatar!