I live in San Francisco. do most of my driving in the city. I've read elsewhere that Overdrive should only be used on the highways when cruising, and really not anywhere else. I've always had Overdrive on permanently and notice very poor lows. Turning it off results in better city MPG as well? which is what I'm looking for.

Your thoughts?

 

if you do alot of city driving, durning OD off, and/or using power mode will supposedly help mpg, on the basis that it takes less of a jab of the throttle to kick it down a gear or two (probably just 1 gear if you have o/d off... rare that you'll go from 3rd to 1st, but it can happen if you're aggressive enough of a driver) to get the acceleration you're looking for. if you are in comfort mode with o/d on, you're gonna have to push the gas pedal alot harder to get it to downshift into 2nd, plus you have to wait longer before it will shift, so it's that much longer that you're wasting gas before you start speeding up.

I wouldn't say that O/D should ONLY be used on the highway.. once you're out into the suburbs and can go at a nice steady speed for several minutes at a time, then just turn O/D on and let the TCU do its job. Our engines make enough lowend power to drive at a steady 40mph in o/d no problem.. matter of fact the TC locks up at 45mph in O/D. But if you know you're going to be doing alot of speed variation, that's when you really want to leave O/D off.

now on my car which is a 5spd, when i'm driving in the city i tend to shift up very early... staying between 1500-2000rpm but on the other hand, i can immediately downshift into 2nd/3rd and go, with almost no delay, and without having to push the gas (besides a quick blip of the gas to match revs). I do sometimes go into 5th gear as early 35mph if traffic is very light and i'm not going to have to stop or slow down or speed up. but if traffic is heavy i usually keep the rpm just over 2000rpm so i can react faster to unexpected traffic conditions.

 

Thanks for writing that all out..

Another. did you track the MPG gains you got from the Warpspeed?

 

well, i changed a lot of crap at the same time..

in oct 2008 i switched to heavier 17" wheels with wider tread... that hurts MPG. I also switched from a VG5 tranny to a VE5 tranny, which has a different final gear ratio, which can affect MPG too. For a reason beyond my comprehension, one injector totally died while i was replacing the tranny, so that REALLY hurt my MPG (only got 23 on the highway) on my way to Goon's house (2 days after installing the tranny).

There, we put his silver/black engine in my car along with a full rail of good injectors (two of which just failed last week ...) so i got decent mileage on the return trip.. about 28-29mpg. Also switched from stock flywheel to a Fidanza lightened flywheel, and put the WSP ypipe on. MPG seemed lower than usual, but after all those changes, it's difficult to really cite any one part as having increased or decreased my MPG by any given amount. You know what i mean? Plus since i became unemployed i haven't always been able to fill my tank all the way up... sometimes i can only put $5 in at a time.

 

"Overdrive" is unfortunately an unfortunate (sic) term misused by most advocates of its use for fuel consumption improvements while the reality is that there can be very few more complex subjects on a vehicle when you are talking OD wrt fuel consumption on a real-world vehicle and not the engine alone.


To get to grips with the basic fuel consumption characteristics of an internal combustion engine (non-diesel) ..................... I suggest you read and understand this excellent description on one of my favorite sites

So many factors (and often with conflicting results or implications) are involved that no single blanket recommendation should be made imo - factors like personal driving style, comfort, noise, engine wear, gearbox wear, oil film breakdown, cooling, temperature, fuel, surface conditions yada yada yada yada all play a part.

FWIW - my vehicle's condition, driving style and preferences allow me achieve about 8.5km/l in town and 11km/l on the highway with OD switch left in the default on position ........................... and imo from what I have seen getting reported in fuel consumption threads here by other "tweaked vehicle" (headers/tubes/flywheels/ignition systems yada yada yada) owners I am actually doing pretty well in the top percentile of consumption figures with a bog std 3rd gen VG

 

So it I 'should' get a better mpg with O/D off and in power mode?
I do mainly city driving @ 35mph


I always thought that power mode was made for extra power, thus less mpg. and comfort mode would give more mpg.

 

http://4dsc.com/articles/drivetrain/...t_switch.shtml

as for the overdrive like they said, there are a lot of variables to determine whether or not you should drive w/ OD on or off. I personally drive w/ the car in power mode, and the OD on almost all the time.

 

I usually drive with OD on all the time, but a few years ago I tried turning it off for all city driving over several tanks of fuel, made no noticable difference to fuel economy. If you find your driving conditions cause your transmission to constantly shift between 3rd and 4th, then you are probably better off turning OD off, even just for the sake of the transmissions health.

 

Thanks for the link, helped me understand better!

 

I Personally only use overdrive if I know that im going over 45-50 miles per hour for a long period of time, say like on a trip out of town, when the speed limit is 55 and above! While im in the city driving I normally keep it in the off position. Driving with the overdrive on in the city going less than 50 miles per hour, will result in the transmission searching through 3rd and 4th gears, (which feels uncomfortable at times)so I normally leave it off in stop and go traffic. But driveing with it off and going long distances will result in lower fuel economy, because if you watch your revs they get higher which means the engine is turning faster than it would if you had the overdrive on, when you turn the overdrive on the revs will go down.

 

I've found that in areas with hilly terrain, turning off overdrive prevents the transmission from shifting between 3rd and 4th gear constantly. Not only is this annoying, but I would think it leads to more fuel consumption and more wear on the tranny.

Also, on the Power/Comfort switch (89 SE), there is a "middle position" that is neither position. Is this a compormise between the two shift points?

 

Yes the "middle position" for the power/comfort switch is like a "normal setting" if you punch the gas, (heavy throttle), the tranny will shift at higher rpms like in "power mode". And if you are driving cautiously, in "middle position", the tranny can shift below 2k rpm.
generally speaking, "normal setting" is a good place to keep it if you are unsure. And "power mode" is good for hill climbing to avoid the tranny hunt of gears.

 

it's basically a compromise, yea. the middle position, it operates in Comfort until you give it a reason to think you want to go into Power. If you push the down far AND fast, it'll light up the P light and stay in P for a few seconds. If you gradually build up to the same amount of throttle, it will stay in C mode. So how fast you jab the gas pedal is more of a factor than how far you push it.

 

Is this for all the 3rd gens? I could've sworn I've never seen the P light up when in the middle position.

 

all VG autos, dunno about VEs. but if you are in 'normal' and you jab the pedal to the floor, the P light SHOULD come on. i didn't notice it for the first year i owned the car either, then i read about it in the FSM and payed attention to it and lo and behold it did light up.

 

the "P" light comes on when the TCU goes to it's power programming

 

89 only had the VG, so I guess I never noticed it.

Thanks anyways!

 

It is compputer controlled so I let it decide when it wants to go into overdrive. I never had an issue with mine hunting between 3rd and 4th. I have read before about people locking out 4th gear and having long term issues. The transmission was not designed to determine shift points for only using 3 gears except for highway use. You may be stressing the torque converter among other things.

 

It depends on many factors - how steep the hill is, how many people are in the car, weight, etc. At least that's what I've noticed.

On a steep hill with a speed limit of 55, the tranny will go into overdrive, then the car will slow down until it shifts back to 3rd gear, speed up, then shift back into overdrive, etc.

Although the car had a lot of miles on it, so it doesn't work like new.