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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / September 2005Shifting automatics
We have two cars, a stick shift and a 2005 Chrysler T&C. With the manual, considering the high price of gas today, I am really shifting early to save gas. Do modern automatics like the T&C allow you to force upshifts? In older automatics a quick backing off of throttle would usually force an upshift. Doesn't seem to work on the T&C. Do any of the new electronically controlled ones allow forced upshifts, or do they all think they are smarter than driver? >We have two cars, a stick shift and a 2005 Chrysler T&C. With the >manual, considering the high price of gas today, I am really shifting [quoted text clipped - 5 lines] >electronically controlled ones allow forced upshifts, or do they all >think they are smarter than driver? Electronically controlled transmissions leave the operator very few choices about actually controlling the powertrain. You put it very accurately: "...they all think they are smarter than the driver." The best transmissions for operator control, feedback, and overall diveability, were GM Hydramatics built in the late 1960s. That said, most late-model transmissions are heavily biased toward early upshifts, anyway. Little thing known as Corporate Average Fuel Economy (CAFE). Get it into higher gear earlier, reduce engine speed, reduce fuel usage. >>We have two cars, a stick shift and a 2005 Chrysler T&C. With the >>manual, considering the high price of gas today, I am really shifting [quoted text clipped - 15 lines] > Average Fuel Economy (CAFE). Get it into higher gear earlier, reduce > engine speed, reduce fuel usage. And sometimes automatics just get really sluggish if you get it to a point where the electronics decide that absolute fuel savings trumps decent performance. That's not to say manuals are always better. I recall GM got the Corvette's 6-sp fuel economy up in the early 90's with some lockout that forced it into 6th gear. The Saab 900 I test drove in the late 90's had a recommended upshift light on the dash. If I followed its instructions, the engine would buck from being lugged. > And sometimes automatics just get really sluggish if you get it to > a point where the electronics decide that absolute fuel savings [quoted text clipped - 6 lines] > I followed its instructions, the engine would buck from being > lugged. Hey, a three bucks a gallon, I don't mind sluggishness. I get that anyway in my stick when I shift early. I have not had an engine buck from lugging since my cars had FI. Some may, but it is amazing to me with my stick shift Neon R/T. That engine even has a quite agressive cam profile, yet it lugs way down without bucking or vibrating. Hey, the acceleration is almost non-existant, but it doesn't complain. I like many others was taught, many years ago, not to lug an engine, 'cause it was hard on bearings and crank. But in the early seventies, after the first fuel crisis, a European mfg did some extensive testing (I think it was VW) and drove some cars for extended distances really lugging engine, then tore them down and measured results. They concluded that modern oils and bearing materials were good enough that no damage was done by lugging the cars. > We have two cars, a stick shift and a 2005 Chrysler T&C. With the > manual, considering the high price of gas today, I am really shifting > early to save gas. From what I have seen, Don, the automatics of today are pretty fuel efficient, especially compared with the older trannies. If you avoid jackrabbit starts, and watch the flow of traffic so that you don't have to brake or accelerate violently, I doubt that you will save a lot. My complaint with automatic transmissions has nothing to do with economy. It is the expense to rebuild and the lack of warning you may have when they start to fail. If it happens on the road, it can be uncomfortable. > If you avoid jackrabbit starts, and watch the flow of traffic so that you > don't have to brake or > accelerate violently, I doubt that you will save a lot. I certainly DO play the traffic lights. I am amazed at how that bothers folks behind me. They go around me, cut back into my right hand lane, rush to the traffic light and stop. Of course, that gets in the way of my coasting through the light at 30 mph instead of having to stop or slow down further 'cause I am behind them, and they are starting from zero. There seems to be some perceived advantage these days of getting to the light soon enough to stop and take a little break. Maybe that is when folks drink their coffee or fix their hair. The jackrabbit start is something that interests me. One should keep rpm down, but the idea of just barely squeezing the throttle is incorrect. That does not save gas. With my stick car I use moderate- maybe 50% throttle, but shift early. The early shift means I am lugging engine, so don't get blistering acceleration, but I do not use a feather foot. My wife thinks I am wasting gas, but is always surprised when we check milage and it is so good. Using very light throttle is NOT conducive to best milage. The reason is that the actual thermal efficiency is dependent on the ACTUAL compression ratio, not the geometric one, in an engine with a throttle. It is actually concerned with the ratio of the ACTUAL PRESSURES during the cycle. I used to drag race an automatic based car, and tried a lot of combinations. I got the best times when I set the brakes, torqued the driveline, then let off and floored it from idle. No RPM preload or any such thing. That had to be the worst case for economy since it was best between the traps. Maybe there is a compromise somewhere. Heard the other day on CNN that driving a clean car can increase the mileage up to 2-3 %. Minimizing weight is another ploy that could work. That list was several items long and I wish I had it or could find it on the web for future reference. snip > Heard the other day on CNN that driving a clean car can increase the mileage > up to 2-3 %. Minimizing weight > is another ploy that could work. That list was several items long and I wish > I had it or could find it on the > web for future reference. I suspect the dirty car-clean car thing is way exaggerated. That would only make an effect if the flow over most of the car was laminar. It takes a very careful design to maintain laminar flow over an aerodynamic surface- I doubt if it works on cars. Weight certainly has a big effect on city driving. Heavier wieght increases fuel burned to accelerate to speed. Also, people forget that heavy braking burns extra gas. Every bit of heat that goes through brakes ultimately comes from gas tank. Following too closely requires greater changes of speed, more brake use, than greater following distance. Use of brakes at stop lights burns gas compared to playing lights. >Also, people forget that heavy braking burns extra gas. Every bit of >heat that goes through brakes ultimately comes from gas tank. Well, or a back wind, or gravity. Think about driving downhill on a mountain (not that you should be using the brakes to slow your descent). >>Also, people forget that heavy braking burns extra gas. Every bit of >>heat that goes through brakes ultimately comes from gas tank. > > Well, or a back wind, or gravity. Think about driving downhill on a > mountain > (not that you should be using the brakes to slow your descent). How'd you get up the hill? Wind and gravity obviously didn't get you there. A back wind might be "free" gas mileage but then a head wind is exactly the opposite. That part comes out a wash. >>>Also, people forget that heavy braking burns extra gas. Every bit of >>>heat that goes through brakes ultimately comes from gas tank. >> >> Well, or a back wind, or gravity. Think about driving downhill on a >> mountain >> (not that you should be using the brakes to slow your descent). >How'd you get up the hill? Wind and gravity obviously didn't get you there. Yeah, but in that case it didn't have anything to do with one's gas-guzzling driving habits, if you had to get up the hill one way or another to reach your destination. Of course, you could say making the top of a hill your destination is a gas-guzzling driving habit... I wasn't trying to contradict that sentence as much as point out that modifying one's driving habits can't completely eliminate wasted energy through braking (if that was the claim that was being made). Then the quibble degenerates to "what's a 'driving habit'" and "what is 'waste'"... :) > We have two cars, a stick shift and a 2005 Chrysler T&C. With the > manual, considering the high price of gas today, I am really shifting [quoted text clipped - 5 lines] > electronically controlled ones allow forced upshifts, or do they all > think they are smarter than driver? Sure, there are some cars that offer a manual override - Volvo for one. They are there for entertainment more than anything else. Modern electronic automatic transmissions are pretty smart and are programmed for economy, although some reprogram themselves to learn a drivers habits to an extent. Don't expect that you will be able to improve much on the economy of computer controlled engine mated to an modern automatic though. The biggest impact you can have on fuel economy is to take it easy on starts, keep the speed as constant as possible, keep the tires inflated to the highest recommended pressure and don't drive much faster than 55mph on the open highway. |
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