Refresher course?

Discussion in 'Fuel Economy' started by jcp123, Apr 19, 2015.

  1. jcp123

    jcp123 Caliente!

    Anyone care to refresh me on some pointers for freeway driving in an automatic? Got a drive coming up and I'd like to be "on point" as it were. It's about 100 miles, PSL varies from 75 to 60mph, basically all interstate driving. This would be in my slush box-saddled Echo. Road surfaces vary from chip-seal to fairly beat up concrete, maybe a few miles of asphalt thrown in (can't recall). The first 30-40mi are rolling hills, after which it flattens out a bit. Temps look to be ideal, high 70s so I can keep te windows rolled up fairly well.

    I typically run with a constant throttle setting, usually drags me down to 45ish on uphill a to 65mph on the flats. Long downhills, I can start a coast at 50ish and end up around 65-70mph. I do some modest drafting, I typically can stay about 6 car lengths behind a truck and feel I am definitely in the draft envelope. I rarely do this because of course the lack of visibility is dangerous, and if the trucks aren't speed-limited to a reasonable speed (<65mph) it's not really worth it. Few trucks seem to be limited this low. My tires are aired to 48psi. I do not have cruise control.

    What am I forgetting?
     
  2. RedylC94

    RedylC94 Well-Known Member

    Is that at fixed throttle angle even down the hills? In a car as light as the Echo, it seems that would burn a lot of gasoline better spent maintaining speed up the hills. 70 mph consumes a lot of power.
     
  3. ALS

    ALS Super Moderator Staff Member

    100 miles? Easy, park you butt in the right lane and keep her at 55 mph when the posted speeds are 55 mph and up. If I remember the highway gearing has a lot to be desired with the Echo's small 1.5l motor, so keeping the rpms down is your main concern.
     
  4. JohnM

    JohnM Well-Known Member

    Inflate tires to maximum sidewall.
    John
     
  5. ILAveo

    ILAveo Well-Known Member

    You want to keep/get the torque converter locked up, so on hills you'll want to play with the throttle a little when you're around the lock/unlock point. I've never driven an Echo, so I'm guessing it unlocks before you're down to 45 when you're going uphill. You might want to add a little extra throttle a bit after starting up hill before you get to the point where the torque converter unlocks.
     
  6. jcp123

    jcp123 Caliente!

    No, coast means coast - in N, engine on of course. The curse of automatics. On some of the smaller hills, though, would it be worthwhile to throttle up and then coast down rather than keep constant throttle up and down?
     
  7. jcp123

    jcp123 Caliente!

    RPMs are apx. 2450 @ 60 in mine. Not great, not bad. I end up staying around 2100 as a whole, though, a bit above 50mph.
     
  8. jcp123

    jcp123 Caliente!

    At 48psi, I am 4psi above sidewall. I have a magician's mix of tires, otherwise I'd be at 50 all around.
     
  9. jcp123

    jcp123 Caliente!

    Unless I do big throttle inputs, I don't come out of lockup below 40 mph. Lowest unlock I have seen was at about 36 mph, about the minimum speed the car will engage lockup when accelerating.
     
  10. JohnM

    JohnM Well-Known Member

    1. Run with the windows up and closed. Suffer a bit unless you have A/C. Avoid the A/C if you can.
    2. Fill up with Ethanol free gas.
    3. Don't draft, but find a big truck going your speed and stay the legal distance behind it.
    4. Depending on outside temperature put a piece of cardboard in front of the outside radiator grill, but check water temps. Remove the cardboard if water temp exceeds maximum.
    5. Change your oil to synthetic (assuming you needed to change the oil anyway)
    6. Wax your car before you leave.
    7. Remove your car antenna.
    8. Do not pass anyone, if you can avoid it.
     
  11. ILAveo

    ILAveo Well-Known Member

    If your transmission can do engine off coasting that would be the way to go. You can do math that tells you that smoothing your speed towards its average helps you reduce your total average air resistance for any given average speed. I generally try to run a slightly higher throttle up hill once my speed drops below my target average speed.
     
  12. JohnM

    JohnM Well-Known Member

    One other action you can take is to remove as much weight as you can from the car. Look in the passenger compartment and trunk for unneeded items.

    If you want to go all out, remove seats you will not use.

    Could also remove the jack and spare tire (buy a charged can to inflate a flat tire).
     
  13. RedylC94

    RedylC94 Well-Known Member

    That's definitely true, and is a point too often overlooked. The optimum compromise between fixed throttle and fixed speed depends on numerous factors, including aero drag of your particular vehicle, its weight, length and steepness of the hills, transmission behavior, other traffic, etc.

    I'd think it would take a pretty serious hill for an Echo to start down at 50 mph and reach 70 mph coasting down.
     
  14. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Dallas? That's what the terrain and road surface description tells me. :p

    Yeah, biggest thing is keeping it in top gear. Get a running start for those hills, bleed the speed off as you climb. My van will hold top gear until 40 mph, so I'll hit the climb at ~60 and bleed it down to 45 by the crest. Then regain the speed going down, for the next climb. Better to run a few mph too high than be forced to downshift. Use the gas pedal to balance between too heavy = downshift and too light = too slow = downshift.

    Once it flattens out, it's a simple speed vs mpg situation. Play some p&G with the waves of traffic. Speed up in a cluster for smoother traffic flow, then coast down when they pass and the road is clear.
     
  15. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Wow , your social conscience is more developed than mine, Andrew. I usually hold my desired speed and let ' em fly by me. But we don't have "waves" here, at least not in the afternoon rush.
     
  16. JohnM

    JohnM Well-Known Member

    1. Check the weather forecast and if possible plan your trip so that:
    - the wind is behind your back
    - you do not drive in the rain
    2. Use tires with a low rolling resistance
    3. Use Pulse and Glide technique on flat roads, as well has hills. If traffic allows and your car manufacturer does not forbid it, do the following continuously while on the road: Select a speed range where you will pulse and glide, e.g. 50-60 mph or 50-55 mph. Then accelerate very slowly to the upper speed, shift to neutral (if state laws allow shifting to neutral while moving) and coast or glide down to the lower speed. And repeat. Always coast down hills.
     
  17. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    I don't think the State of Illinois knows whether or not I'm in neutral.
     
  18. jcp123

    jcp123 Caliente!

    Yup, to Dallas. I start my new job there tomorrow!

    Engine off coast is a negatory. Engine driven pump so damage could result. At 255k mi, I don't think I'll risk it. Keeping it in top gear/lockup is no concern.

    Car is pretty light since I don't keep junk in the car. I actually don't have a spare tire ATM, it went flat and the spare wheel is so bent that 7oz of wheel weights still can't balance it!

    I am intrigued by the idea of throttling harder up the hills; I am hearing different ideas, should I try to keep a set speed up the hills, or simply use throttle to keep from bleeding the speed as quickly?

    P&G...for some reason I am intimidated by this technique and always have been. Perhaps if the traffic is light, I'll give it a try. On the pulse, being that it is an automatic, is it worth trying to throttle it hard (high load value/decreased throttling loss)?
     
    Last edited: Apr 20, 2015
  19. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    P&G with automatic is tricky, but can be beneficial. Especially with poor gearing like you have. RPM is king still, so you have to manage that first. Then, within the confines of that, go ahead and push the throttle just short of the point where it unlocks and downshifts. It consumes more fuel in the moment but a higher percent of what it consumes turns into power. Then go into neutral and coast. Watch the trip average mpg and work to make it go up from cycle to cycle.

    At highway speeds the benefit to FAS is very small. Don't sweat it. I don't in the van on the highway. It's a big benefit in town at 25 mph.
    10 mph at (my) 0.22 gph idle = 45 mpg
    20 mph = 91 mpg
    30 mph = 136 mpg
    40 mph = 182 mpg
    50 mph = 227 mpg
    60 mph = 273 mpg

    What's the practical difference between 273 mpg and infinite? Not a whole lot. That's a tablespoon of fuel per mile.
     
  20. jcp123

    jcp123 Caliente!

    Well I racked up 47.2mpg including a missed turn. Eh. I was hoping to push 50. The heavier throttle up the hills just doesn't seem to benefit in this car?
     

Share This Page