Approaching hills, technique?

[electronumpty]

Hi all,

I've had some success with my car.

There are no mods on the car, except for the new cruise control.

The only thing I have done is to turn off the air con.
I have 15" wheels which were set at the higher pressure as listed in the back of the diesel filler cover.

I regularly average 68-70mpg and have got 82mpg on a couple of occasions.

As for driving style I am a believer in the clutch down technique while coming up to roundabouts, red traffic lights and stationery traffic all at slow speeds.
I suppose both of my high mpg top scores were possibly due to very big hilly journeys through the Cairngorms and Lakes?

I suppose this is a form of cheating as the car will be in idle for short spaces of time. When I wasn't trying this technique fully I was getting 65-68mpg.
Though it's interesting how much extra you can get by "coasting".

When the wife does the school run the best she got (though she couldn't give a crap about mpg) was 52-55mpg though that was only a couple of times and she had the air con on and the car needed a service.
The other thing was that I added the redex diesel additive.

Though the last 4 fill ups have lead me to believe it only adds 4mpg to my overall score. Not sure if the extra cost in buying redex is beneficial for that extra mpg.

[Draigflag]

Hi there. Im a self confessed coaster too, like I said earlier, there is a long down hill section locally that I can coast 6 miles down, using very little fuel indeed. I have found if I set my cruise control to 60 MPH the car will accelerate up the hill and maintain 60, but not sure what the effect on fuel consumption is. Its the uphill thats the killer!

[nissanb14]

You wanna increase speed as your going downhill. by using gravity for free energy!!
Never ever accelerate going up in a hill! just use the energy that you have to go up the hill with taps of light accelerations!!
Put the car in neutral when you are going downhill!!

Never use Cruise control on hills!!! the engine will brake going downhill and accelerate going uphill!!

[Draigflag]

I always use neutral going down. When watching the range reading, I can loose about 70 miles going up some steep hills. On the way down, that range can then go back up by about 50 miles in neutral.

[Jcp385]

Hills really do suck. There's a good long one which kills my commute home, shaves probably a good 2-5mpg off of the whole thing. Then again, the alternate routes are even worse.

It's long and relatively shallow, but it's right after a dead stop. I generally utilize low-mid throttle to get up over it and then maintain that throttle until I reach the PSL, at which point I back off. I tried muscling up the hill and reaching PSL much sooner (which also gets me into top gear and TC lockup sooner), and the results were dismal.

Otherwise, as stated, I try to use my momentum. Bleed speed up the hill, coast and/or gain speed back down it depending on what comes after the hill.

[Draigflag]

Thanks for the tips, I too see 5 to 7 MPG drop off my average on some hills, still haven't nailed a technique yet! I was considering using cruise control, set it at say 50 or 55 and just let the computer use just the right amount of fuel to get up and over the hill.

[Jcp385]

In my experience, the cruise control doesn't do a stellar job. It'll let the speed drop then aggressively adds power to re-accelerate - uphill. Newer cruise controls might have some better logic, though. Newest car I have had with cruise was a 2004.

[BDC]

You should judge your speed over the crest of the hill based on how steep the downhill side is. If you can coast in neutral without gaining or losing speed, then it doesn't matter what speed you top the hill at, because in neutral you'll just stay at that speed. If you can gain speed while coasting on the downhill side, you should slow down as you approach the top, so that you don't waste energy maintaining speed that you just have to throw away with the brakes on the downhill side. If the hill is not steep enough to maintain speed in neutral, I like to accelerate over the hill and then coast as long as I can without holding up traffic behind me. In a similar manner to pulse and glide, except with longer glides. (I'm not really a fan of pulse and glide in practice, except on hilly terrain).

On a hill of the proper slope, sometimes you can actually use less gas to get over it than you would driving the equivalent distance on flat ground. This is because gasoline engines are increasingly efficient at increasing load (not increasing revs -- increasing throttle). If you can climb the hill without downshifting, and then coast in neutral all the way down, you store up all that energy at higher efficiency (full load) and once you reach the top, coast in neutral all the way down and you don't pay the internal engine friction of driving at cruising revs.

It costs gas to keep the engine running at idle, but it costs less in gas to run the motor at idle speed than it costs you in momentum keeping the car in gear and spinning the motor at 2,000+ revs. Hence why you shouldn't necessarily coast in gear unless you need to bleed speed off, or unless you know there's a stop light or obstacle at the bottom of the hill. (Or, if it makes you feel unsafe or uncomfortable.)

Of course this doesn't go for diesels, because diesels are the opposite (decreasing efficiency at increasing load).

Almost all of my best tanks have been on hilly road trips through the rural parts around here.

[Draigflag]

I always go in neutral down hills, some are so steep that I let the car speed and go over the speed limit by 10 or 15% (i dont speed that often anyway) and the more speed the car gathers, the longer it will last once flat ground has been reached. Your comment about diesels, diesels are more efficient when idling are they not? You can leave diesels running all night like a generator and they dont use much fuel, so I assumed they are pretty effecient when idling.

[Quadrunner]

I always think of it this way. If you ever feel your engine start to bog down a little its running richer, so there is a little gas that is not getting used to its fullest potential. That is not a fact. That is how I justify my actions. I get my best mpg on hills because I don't use my cruise control. I usually feather the throttle the entire time. I keep the engine running lean as I can while still slightly accelerating downhill, so I can slightly decelerate going up the next hill. I usually maintain speed at the base of a hill and then the more I get up the more I'll let off to keep the engine running lean as the rpm's drop. By the time I get to the top my gas petal is at or around its highest point in the cycle and I repeat. Works good for me!

I never understood the point of coasting in neutral unless maybe its on your final hill or two before a stop. Your engine is still running and you still have drivetrain friction since the drive wheels are connected to the transmission all the time. It seems like your paying for a slight increase in mpg with drivetrain stress from the extra shifting from neutral to high gear. I guess I like my car too much. There is also the consideration here that the more your speed fluctuates, the more you will lose to air drag at the bottom of the hill. If you feel your car begin to near terminal velocity in Georgia overdrive, its a good indication you could be doing a little better. Just my humble opinion. I don't have the computers to back it up, and my newest cars have historically been about 15 years old.