06 FX4. Most of my commute is 35mph to 45mph. The truck will shift into overdrive and not hunt when I can stay at a steady speed and the traffic is flowing. But this is not always the case. I'm wondering if it is beneficial or will it help extend the life of the transmission to lock out overdrive for city/rural driving.

 

Only if it is hunting. If it can stay in OD and the TC is not locking and unlocking, leave it in OD.

 

While I agree with kingfish I lock mine out anyway when I am putting around town. It may cost me some fuel mileage. From what I have seen overdrive is usually the weak link in most transmissions and it is usually the first to go on you so I only use it if I am traveling at speed and not towing.

 

I leave my OD off when in city traffic or I know that I will not have long runs at a minimum of 45 to 50 MPH. I feel that I get slightly better performance in slower traffic with the transmission in drive instead of shifting between drive and OD. Plus, I always felt that overdrive was intended for long runs at highway (50 plus MPH) speeds.

I know a former automatic transmission mechanic that constantly recommended this with 'other brand' automatics, and suggested it for all overdrive automatics. His reasoning was that the higher RPM in drive versus overdrive at the same speed caused better fluid flow in the transmission, keeping the internal parts cooler in the long run. Also, constant lock and unlock of the TCC and shifting in and out of overdrive causes unnecessary stress to the transmission. He also recommended keeping a minimum RPM of 1300 to 1400 RPM in overdrive for good transmission fluid flow. I really could not argue with this logical explanation.

 

Same here. I use my OD only for highway driving. Above 60MPH. I have always done this with all my OD vehicles and never had any tranny issues.

 

Everyone has confirmed what I was thinking. I always locked out OD with my Bronco. I don't know why I wasn't doing it with this truck.

Thanks!

 

MX I have some P-shops waiting for you.

 

if u get better flow in d vs od- then why lower tft's in od?

 

Openclasspro#11,

I have seen with my own eyes a LOWER transmission fluid temperature at the speeds that the OP was questioning about (35 to 45 MPH) in my vehicles by locking out overdrive versus allowing the transmission to shift in and out of overdrive and lock and unlock the torque converter clutch whenever it felt like it. There are so many variables between your experience and mine (driving style, vehicle parameters, PCM tuning, weather, terrain, traffic conditions, etc.) that our experiences could be totally different, just like two different drivers in two similar vehicles could get different MPGs on the same trip. As you are a small fleet owner, I believe you can see through maintenance logs and fuel receipts which drivers are easier on your equipment than others, and see that no two drivers and vehicles are exactly alike.

As for the automatic transmission mechanic I refer to, he has OVER 30 YEARS of hands on, personal experience in an independent, family owned transmission repair facility that has currently been in business for over 55 years. He has seen many a transmission fail due to being in overdrive at low speeds and the 'overdrive hunt and peck and torque converter lock and unlock syndrome' at 35 to 45 MPH that he has lost count.

Again, openclasspro#11, there are so many different variables between your experiences and mine that bring us to different conclusions on this question. The OP asked for peoples opinions based on their experiences, and I posted my experiences with the subject at hand. I did not crap on anyone elses experience that was different from mine, nor will I crap on anyone elses experience that is different than mine, because I know that there are MANY variables involved when talking experiences with vehicles and opinions on what is right and wrong.

 

not argueing- just curious=i notice this in my 8 vans at highway speed~65 -lower tfts in od that d-same as was with my 01 sc'ed ram, 03 f150,and wife's 08 f150-must be because i'm at higher speeds than op?

 

It's because it's STAYING in OD and the converter is staying locked.

 

but id d flows more fluid-wouldnt that bring temps down lower than od?

 

At 35 to 45 MPH, locking out OD and staying in drive is better because you do not have torque converter slippage causing unnecessary heat.

At 65 MPH in OD, the TCC is locked, and the RPM is lower than in drive at that speed.

Where I said that being in drive versus OD is a benefit is at the speed the OP was questioning, not at 65 MPH (one of those variables I discussed in my second post in this thread).

 

Where?

 

Less shifting is always better! I do this every day. As soon as I start my truck I turn OD off until I need it.