Civic city driving, D3 or D?

Hi Group,
I am an owner of a 05' Civic, which comes with an auto transmission. I have always been driving with D, until I accidently read about the D3
shift yesterday.
The owner manual claimed that in stop and go situation, driver should put the shift in D3 so that the trans will not be shifted to the 4th gear. This makes sense to me. However, I still wonder if I should do this in my case.
I drive about 8 miles each way to work. There are several cross sections so normally I would be stopped several times. However the city speed limit here is relatively high (40mph). When I put the shift at D3, at a speed of 40mph, I feel the engine does not have much more to give.
I wonder if there is a maximum (proper) speed for the third gear. I have never driven a manual car before so I honestly have no idea.
Also just for the sake of curiosity, at 40mph, which gear will yield a better gas mileage per gallon, the third gear or the fourth?
Thanks a lot!
Regards, Doug
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I believe what is says is that the stop and go has to be a span of a really short distance. D3 is a great choice for driving in a crowded downtown, but if the distances between stops increase then put it on D.

About 39mph.

39mph is the point where it'll shift to fourth. My best answer is fourth.
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wrote:

If you put the peddle down in third gear at 40mph it will go like hell. It may even downshift into second. You are hearing the engine rev a little and it is scaring you. The engine could run forever at that speed but it will be quieter and get better mpg if you let it shift into fourth.

39 is a fine place to shift into fourth in normal use but it is nowhere near the maximum speed in third.
As for when to use D3: if you find that the transmission is shifting between third and fourth (due to terrain, fluctuating speeds, barely shifting into fourth before you let up for the next light) then use D3. If it is staying in fourth for at least 20 seconds each time it gets there, then use D4. The only other time to use D3 (or even D2 or D1) is in descending grades. In that case, use whatever gear is necessary to keep brake use at a minimum.
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The maximum proper speed is 39 at half throttle on a flat road, but the maximum speed is 96 or where ever the rev limiter ends. The proper speed is based on engine lugging, or throttle position. The proper speed is programmed by the automaker. If you asked them, they would say the proper speed for 3rd gear is 35-96 based on throttle position.

D1 is mainly used for slippery conditions such as snow, ice at low-speed. Descending on D1 could be damaging to the transmission when up-shifting, and the chance of over-reving is high.
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wrote:

I don't doubt that 39 is the optimal shift point set by Honda engineers for certain conditions, but forcing it to into a higher than optimum rpm (within reason) won't hurt anything. For example, in descending a long grade, if third gear keeps the speed at a safe 45 or even 50 then that is the gear that should be used.

D1 could be damaging on upshift? I don't think that makes sense. If you mean that it could be damaging to downshift into first at too high a speed, that is theoretically true but I don't think the AT will actually allow that to happen. Descending in D1 (if that option is even available) would be for extreme grades. If the hill is so steep that it would over-rev in D1, you may have to use the brakes to keep the speed *very* low, like 5 mph. Better yet; find another road.
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Doug wrote:

the owner manual for this vehicle or for some other automatic?

that engine will still pull in D3 at 90+mph, so "the engine does not have much more to give" isn't anything to worry about.
bottom line, the transmission control on that vehicle is all electronic control, unlike old fashioned autos. sophisticated shift algorithms mean it doesn't shift back and forth unnecessarily. and better than that, it also "learns" what patterns work best for your driving style and usual trip routing. just leave it in D and forget about it.

yes, it's up near 90mph.

4th, on the flat.

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