I have been driving a lot more highway miles (900 mi round trip) each month and I was wondering if any one knew the "sweet spot" to set my cruise to for the best gas milage. There must be a point where my engine is running at optimum efficency in 5th gear (97 4runner 3.4). So far I have been setting it to about 2700rpm about 73mph and I have been getting 19-20ish mpg on 87 octane gas.

Any thoughts?

 

Those numbers sound pretty good to me.

cnn/edmunds test

 

I have heard 68 mph is the most efficeint speed.

 

I say it's not so much the RPMs as the throttle position. Remember you can be going down a mountain pass at 4000 rpms with your foot off the gas and use no fuel at all.

 

i too get the same numbers at that speed!

 

Sounds about right for me too. With the 3.4L my RPMs are just a little bit below 2200 and that's running 33's on 4.30 gearing. 68mph is my sweet spot for mileage, although I do get pretty good mileage at 80 too. Anything between 68 and 80 just kills my mileage though.

 

For me, its about 60-65 MPH. Any higher and then MPGs start to fall rapidly.

I can get about 17-18 MPG doing 65MPH, and about 15-16 MPG doing 80MPH.

 

It depends on quite a few things including your tire diameter, gearing, whether the engine is NA or S/C'd, 5 spd or Auto, even air temp outside, etc. My truck, with stock 4.10s, 265/70R16's, NA auto cruises on a flat highway best at about 68-72 MPH (usually more precisely 69-70, but depends if it is summer or winter). If you are really curious, you should get one of the www.auterraweb.com PDA based OBD reader because one of the many functions it has it to get real-time fuel economy (you can do either instantaneous or avg readings). That is how I found the "sweet spot" on my truck and you can see what factors affect it too.

 

stock '02 w/ ect on and cruise control (flat) about 2300rpm's @ 73mph is usually sweet, i have seen 21+mpg.

 

i got a 98 SR5 4x4 w/ the 3.4 V-6. Auto. got a surf board roof rack on top and thats it.

Usualy cruise the florida high ways w/ the 2 front windows down and the rear either half way or all the way and A/C off.

i do 70 at 2,100 RPMs
i do 80 at 2,500 RPMs
i do 90 at 3,000 RPMs
i do 100 at 3,500 RPMs


When i do long trips on th ehigh ways (90% highway) w/ the Average speed about 70-75 MPH (80 on Highways, 60-70 on US-1, and then 30 throuhg the small town) i get 17 MPG. that is with no gunning it to pass ppl and what not.


w/ about 60% suburban (45-55mph speed limits) and 40% highway i get 17-17.5 depending on how many stop lights i hit (i like to jackrabbit red lights and outta neighrohoods and wha tnot)

w/ off-roading... gas milage goes down to about 16.

 

I wouldn't really post those high speeds on here, you'll get a few responses you won't like from more mindful members...
The best way to find that "sweet spot" is to get ahold of a scan tool with the parameters. When I was at GM the master tech showed me what to look for, but I don't remember all of them. A few of them was Air/fuel ratio and fuel trim. Why fuel trim, I don't exactly know.