I have two questions about my Fit MT:

1. Does it hurt the engine, transmission, or gas mileage, to use the cruise control (manual transmission) when going up long grades?

2. If I'm not using cruise control, and I'm going up a long grade, is it ok to stay in 5th gear if the car still willingly accelerates in that gear? For example, yesterday I was going about 70 MPH in 5th, and the engine still had plenty of pep while climbing. (Obviously, if I were climbing that same hill at 40 MPH I know I would have to downshift to a lower gear, but at 70 MPH it was ready to run.)

A friend of mine says:

1. I should never use cruise control for hills, only for level ground.

2. I should not go up hills in 5th, with or without cruise control, even if it freely accelerates.

Is he correct?

Thanks in advance, Any information will help.

 

1. It doesn't hurt much to use cruise control for hills, but it does waste a lot of gas to do so because the cruise control tries to keep the speed and doesn't care about gearing so if it's in 5th and you're going up a hill, it will most likely floor it in an attempt to keep the speed. So I would say your friend is right to use it for level ground, and not for hills.

2. If you've ever ridden a bike up a hill, you'll know how it feels. Even when you can accelerate on that gear, it'll probably be easier to go down a gear. And it'll be less stress on the gear and engine.

I think it all depends on the grade of the hill... if it's only a slight upgrade, then I stay in 5th as long as it doesn't feel like I have to give it a lot of gas to go. Otherwise, I'll always lower a gear... easier for my baby, and easier on gas~

 

I'd say the CC is fine untill you find yourself lugging the engine up a hill. The CC should sense this and kick itself off but I have not had that happen on mine yet so not sure how it's set up. Other cars I've had will disengage from CC when the RPM gets to low for the gear your in. Your foot may do a better job of controlling speed over a hill but it won't "hurt" anything by letting the CC do it for you (may hurt your MPG). It's a balancing act to choose to go to the next lower gear or not, to many variables to say one way is best all the time. More important for me is not to lug the engine, then to get the best MPG while going up long grades. IMHO luggin a small gas engine is just sending it to an early death.
PS
as a rule for driving commercial trucks up hill if you can gain ground speed when you give it more throttle your in the right gear,,,if you give it gas and don't gain speed you need to go to the next lower gear (your luggin it)

 

I make that decision based on throttle position. If I can pull the hill in 5th gear w/o having to push the gas pedal further than I would in 4th, then I stay in 5th. If I have to give it more throttle in 5th, then I downshift. Any time you have to floor it to hold speed, you need to downshift. Since our cars are DBW, it's not 100% accurate... 75% of the pedal position is not always 75% throttle position, but it's reasonably close (I think).

Regarding cruise control. It's goal is to hold a constant speed, not get maximum MPG. W/o using cruise, you can get better MPG on a long hill IF you let the speed drop off (to whatever speed you can hold with the least amount of throttle position). If you are going to manually hold your speed at whatever it was on level ground, then you are doing exactly what the cruise would have done anyway.

 

When my friend told me not to use cruise control when climbing hills, and not to climb them in 5th gear, he did not give me the reasons why, only that I shouldn't. Being the inquisitive (some say stubborn) person that I am, I always want to know the reason why I should or should not, do something, and you have provided it to me.

I truly appreciate it. Thanks to all of you.

One thing for sure, I will not be using cruise control when climbing hills anymore, and I won't be lugging the engine either.

 

blah! I NEVER take advice if the advisor doesn't provide a reason

 

I agree with this as well. If you didn't have CC and could make it up the hill in 5th without too much difficulty, I see no harm in leaving CC on. If you would have required a downshift or a great deal more throttle, then CC probably wouldn't be a great idea.

It won't take you long to figure out what type of grades you can keep the car in 5th for. On my recent trip, there were actually only a couple of spots that I really needed to downshift for. For the 5 speed, highway speeds actually put your RPM's in a pretty good spot as far as the torque goes, so it actually responds allot better than I figured it would.