Hypermile 1992 4Runner

[waddie]

I just bought a 1992 4Runner in EXCELLENT shape. It's a 5 speed with a V6. I'm excited because it's everything I want in a car plus back in those days the Toyota v6 was much smaller than the one they build today. My question is how to get TOP mileage. I just bought it, replaced the plugs, rotor, and distributor and changed the motor to synthetic. This weekend I will change the rest of the power train to synthetic. Next week I want to buy tires but I want to get the right size and tread conducive to high mileage. Any suggestions? Also besides wires, air filter and fuel filter what else can I do for TOP MPG? The wheel bearings aren't loose but would synthetic grease make any difference? Should I spend the time and money to fab up an under body pan for wind? Remember it's a 1992, I'll consider ANY modification.

[waddie]

Also does anyone make a better injector I can replace my existing ones with for better mileage?

[EH3]

install OEM tire size. air them up to the max psi on the sidewall.

tune up. replace o2 sensor. possibly a partial grill block.

in all seriousness, the only way to get good mileage out of an SUV or truck is to slow down. they are typically as aerodynamic as a brick so the less speed the better off you are.

[waddie]

Will do! Thanks. My goal is 20mpg mixed driving and 24 - 25 highway. Is that goal possible?

[theholycow]

Welcome. Hang around and read other threads, you'll pick up lots of different strategies to increase your fuel economy (often abbreviated to FE). You seem very interested in modifications, which is great; lots of people talk about them, but it sounds like you'll actually DO them.

You're going to shop for tires; look for tires that can handle more air pressure. The more air pressure you use, the less rolling resistance you'll get from your tires. The limit is either going to be the maximum pressure of the tires, or the point at which the pressure is so high that it makes your ride/handling bad (this point differs for each person / vehicle / tire combination).

I don't think you'll gain any measurable FE by changing the type of grease in the wheel bearings. Lots of folks here do skid plates / pans and other aero mods such as lowered front lips. There's grill blocking, warm air intake (WAI), boattails, smooth wheelcovers, antenna removal, and the list goes on and on.

In the meantime, the best thing you can do is work on your driving strategies. Read here about all the different strategies that squeeze more miles out of each gallon.

[theholycow]

Oh, and if you can safely drive on those tires for awhile, do so. Changing tires gives you an opportunity to change the tire size, which affects aerodynamics, rolling resistance, and most importantly gearing. Depending on how it's geared, you might want to change to larger or smaller tires as a cheap way to affect the final drive ratio, but you won't know if you need to until you drive awhile.

What type of driving do you do? Mostly city, mostly highway, rural, congested, etc?

[waddie]

Thanks man. I've been reading posts here for about a year. The problem was the vehicle I was driving I wasn't willing to modify (it was wrecked and beyond repair). My wife's car already gets 32mpg (2005 Corolla) and I really upgrade her's and some upgrades I wouldn't feel comfortable with her using. A few years ago I had a 1997 Chevy Z71 and I took it from 12mpg average to about 17 just with better oil, better gas, keeping it tuned and smaller more efficient tires. This time I want to do it up right.

I shopped tirerack.com yesterday and they measure all performance areas accept FE. I saw a few treads I liked I just want the most efficient. Handling isn't my concern it's economy, I'll run 90psi if I have a tire that can handle it without cupping or blowing.

And I can't lower the clip on a 4x4 but I can put a pan on it and shave the mirrors and roof rack. I honestly don't care how hard it is to drive or what it looks like. I need 4-wheel drive and a tow hitch. I don't care how crappy it pulls just that it can if I need it to 6 times a year.

[waddie]

I do mixed driving. Work is 10 miles highway to 2 miles city/standstill. I love that it's a 5-speed. And will change the tire size if I need to I just don't know if I need to go up or down. I've always assumed smaller was better. Less power to turn and tpyically more narrow with less resistance. My family has always religiously checked fuel economy. My dad had a 2000 Ranger; he drove 30,000+ miles a year and someone gave him bigger tires free. His fuel economy went down like 22%. His free tires (at the time of $1.50 fuel) actually would have cost him $1,000+ in fuel on the life of the tires.

Anyway any tire model suggestions?

[theholycow]

For tires with an efficient tread pattern, look for tires rated as quiet and smooth. I'd guess that if the tread isn't noisy, it's more efficient. If you really plan on doing off-roading stuff (you mentioned not being able to give up ground clearance) you're going to have to balance efficient tread pattern with off-road traction.

The on-road handling issue isn't a matter of how hard you can turn; you'll find that increased pressure makes tires respond quicker and hold better in turns (because the sidewall is stiffer, which makes the tire roll sideways less, which keeps more tread on the ground and less sidewall on the ground). The problem is that at too high a pressure they get bouncy on bumps, acceleration traction disappears, and most imporantly braking traction can be affected. On my full size pickup, 80psi is great in the front but marginally too high in the back with an empty bed; it gets loose when the road is wet. That's okay because I enjoy a little fishtailing once in awhile.

I just did a quick googling and it seems that your curb weight is probably 3800 to 4200 pounds. I'd guess that 60psi would be a good pressure for you. Be sure to check the wheels for their maximum. The max on my truck's wheels is 50 and I've been running 80 for 120,000 miles but I could just be lucky to have not cracked a wheel.

I'm interested in your mirror-shaving plans. The mirrors on my truck have got to cost me at least 1mpg, maybe more, but I need to see well, stay legal, and not look weird (thereby attracting traffic enforcement attention). If I could shave them and not look terrible, I'd consider it, and then shut put them back on when I'm towing.

What do you tow?

[theholycow]

Smaller tires will effectively lower your final drive ratio, making it easier for the engine to move the vehicle but requiring higher engine speed for a given driving speed. Good FE generally involves low RPM, so if you have to cruise at 3000 rpm on the highway then you won't want smaller tires. OTOH, if you have to burn up your clutch and keep it in first gear in the city, you won't want larger tires.

Also, more minor concerns with tire sizing are aerodynamics, weight, and rolling resistance. Larger tires hold more air, and have less rolling resistance (all other things being equal), but have more aerodynamic drag and are heavier. Smaller tires (narrower or shorter or both) will have more rolling resistance (again, all things being equal, especially air pressure).