Let's say you are driving up a moderate to steep incline on a mountain road at a steady 40 mph. What would be the best gear to keep your manual tranny in to obtain the best MPG?
5th gear or
4th gear or
3rd gear or

 

Kinda hard to say, IMO - whichever gear (depending on what your speed is) that puts you at or near the engine's torque peak would give you the best gas mileage. In the 3.0 VQ - that would be around 4000 rpm.

 

I'd say 3rd, even though it's a higher rpm, the engine won't be straining that hard and the throttle opening shouldn't be as great as it would if you were lugging in a higher gear. If it's really steep and at a higher elevation, 2nd might be a good joice too.

 

I believe that if you "lug" the engine, that is you're going too slow for that gear and don't downshift, the motor will be less efficient. That's why 5 mph EZ Pass is so annoying, you hate to throw it into 1st but it's too slow for 2nd.....

 

That was what I was trying to say. A higher rpm but a lighter load on the engine equals less gas. A low rpm, but high load on the engine equals more gas and higher cyl. head temps.

 

I'd say 4th gear. The manual says to shift to 5th at 37 MPH for fuel economy, but going up a hill is kind of hard to say. I don't think you'll feel the car "lug" unless you're doing 28 MPH in 5th. According to my dyno sheet, my Maxima makes 162 ft-lbs and 55 HP to the wheels at 1,800 RPM. If you're in 4th gear at 40 MPH, you'll probably be around 2,500 RPM. My Maxima makes 80 HP and 165 ft-lbs of torque at 2,500 RPM. Not too different, but I think the Maxima makes very little power below 1,500 RPM...definitely not enough to go up a hill without a little lug.