[This followup was posted to alt.autos.ford and a copy was sent to the
Typically the only time you would disable overdrive would be:
1: lots of short up/down hills causing the transmission to shift in and
out of overdrive often.
2: Towing or carrying a heavy load that causes frequent shifting.
3: Going down long hills, where disabling it will help engine braking.
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One can drive in either drive position without causing damage.
The only difference is, if you drive above about 40 MPH with OD
(fourth gear) locked out you will be driving in one less than top
gear and use more fuel by running at a higher RPM. There is no
need to run with the OD locked out because the tranny will not
shift to fourth when the conditions are not right for it to do
so, no matter what you may hear to the contrary.
Sha Zam wrote:
No need to EVER lock out the OD..... wow.. what a foolish thing to say. It's
much better to run in 3rd and keep the converter locked up than to leave it
in OD and burn up a tranny because the converter unlocked and overheated.
When pulling a long grade or a trailer he should downshift to 3rd... no
matter what you say to the contrary.
years ago, on my 87 caprice, it was suggested to keep the car out of
overdrive except when at highway speeds, on a fairly level grade. I believe
electronically controlled transaxle assemblies put and end to that though...
Every once in a while, I still find myself in the D gear, by habit.
I've always kept mine in "O". It's similar to keeping it in "D"; it only
changes into the highest gear when conditions allow it. The only time I can
remember not using the "O" setting was when driving in the mountains.
I did this in my 1989 Taurus and I do it now in my 2000 Taurus. Doesn't seem to
hurt anything and the fuel economy is the best it's going to be, given my heavy
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