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Post edited 4:38 pm – March 14, 2011 by Mike Magee

Carol, I'm no mechanic or expert but I'll try to relate my understanding of it.

Liter size… forget it.  Quite often the larger displacement engine has more horsepower, but not always.

Two engines of the same HP can have different amounts of torque, depending on things like the diameter of the cylinder bores and the length of the piston stroke, stuff like that.  HP is relevant, but the amount of torque being applied to the drive wheels is more important.  Note that I say the amount being applied.  I say that because you can in effect apply more torque by shifting to a lower gear.

Do not worry about "challenging your engine" in mountains.  Actually the bigger issue might be whether the transmission is being challenged too much… it depends on the design of the transmission, but the best thing a person can do for the benefit of the entire drive train is to downshift and to take the hill at a moderate speed.  Charging up the incline and trying to maintain full highway speed is very hard on the tranny; it will heat up beyond its normal operating temperature, and heat is your tranny's enemy.  An auxiliary transmission cooler is valuable protection, but it won't always save a person who abuses it by pushing it too hard.

Some folks go so far as to get a transmission temperature gauge installed, so they can watch the actual temp and know if they need to back off.  The Scangauge II is one device that displays this (and other) info for some vehicles; I'm not sure if it will interface with the Mitsubishi.

Remember that your trailer acts like a sail and the wind resistance builds exponentially as speed increases.  But by the same token if you drive the steep grade in 2nd gear at 35 mph, the wind resistance is quite low and you probably aren't straining things much differently than running 65 mph on the flat.  I towed up and down some very steep grades (as high as 14% IIRC) last summer in Colorado, Utah, and New Mexico; instead of the normal 4th gear (overdrive lockout) I would shift to 3rd or occasionally even 2nd and slow down.  I got through the hills without incident and since that trip my 270 HP V6 Highlander has still been towing my cargo trailer every day for work.  Don't worry about holding up other traffic, because if the grade is that steep there probably are too many curves to be going much faster anyway.

One more thing: you can run your transmission in the lower gear all day long if you want to (assuming you aren't exceeding 'redline' RPMs) and the only downside is the increased engine noise.  It is not the least bit harmful to the drive train… in fact it puts less strain on the components, not more.  For example, my Toyota could travel 60 mph in 3rd gear all day and I would not be harming it.  It would use a little more gas and sound louder, that's all.  So if you ever feel concern that you might be straining your vehicle, don't hesitate to downshift; your transmission will thank you.

I hope that helps.