If you're a professional racer and your car is fully sponsored, then you probably don't care about this. If you have a daily driven car that you take to the track once in a while, then you might be concerned. Read on. If you happen to be a transmission expert, please post your thoughts.
Last night, I was cruising on the freeway going the usual 80-85 MPH. I was commuting between two cities that are four hours apart. The regular flow of traffic stayed in the 80s, not just short bursts of higher speeds along city freeways. With the stock gearing in my 4 speed auto transmission, the RPMs were around 2,400-2,550. This is a comfortable cruising range. The engine wasn't screaming hard and there was only light engine braking when I let off the gas pedal. The RPMs were relatively low enough to maintain fuel economy (I normally get 22-24 mpg in my 4.6L). I was just outside the drone zone so the noise was minimal. I had lots of good throttle response when I need to speed up and I go right into coast mode when I ease off the pedal. I had the DiabloSport Predator hooked up and it was showing my engine coolant temperature (ECT) was holding at 190*F and the transmission fluid temperature (TFT) was steady at 179*F. This is the ideal cruising speed, I think. I was in the groove. I was in Mustang heaven.
Then I thought to myself, what would it be like if I had 4.10s? Would I be able to cruise *comfortably* at 80-85 MPH? To simulate this, I locked out 4th (OD) gear and slowed down to 70 MPH. The tach was reading right around 3,000-3,100 RPM. According to the gear calculators, this is what it would be like with 4.10s at 80 MPH. I held this for a little over a minute and it felt weird. There was a significant amount of engine braking when I ease off on the pedal. It doesn't go into coast mode until I go below 50 MPH. When I looked at the Predator, I saw the ECT crept up to 197*F. I kinda expected that with the high RPMs. What shocked me was the TFT. It had shot up to 200*F! Whoa! This was not good. I have read just about every 3.73 vs 4.10 thread. Some say it won't hurt to cruise at 3,000 RPM for long periods. I say nay nay! At least not without an auxillary transmission cooler. Everyone has their own opinions of transmission fluid temperature concerns but if you read the tech articles on www.tccoa.com and most popular Ford transmission related websites, you'll see that most of them say going above 200* is not good. (Transmission experts, feel free to post up.)
So, what would I do with 4.10s on the freeway? I would have to stay in the "granny lane" and cruise at 65-68 MPH to keep my RPMs at 2,500. With 3.73s, I would have to cruise at 70-75 MPH. The 18-wheelers and minivans would be passing me and that would suck. I'm not pushing for 3.73s or 4.10s in this post. I just want to share what I found and make auto trans owners aware of a possible transmission temperature issue, and maybe get more inputs from the experts. You read this "Don't fear the gear!" thing a lot. Well, if you don't fear the gear, then at least check your transmission fluid temperature. Your highway driving with 4.10s could be hurting the longevity of the transmission fluid.
Last night, I was cruising on the freeway going the usual 80-85 MPH. I was commuting between two cities that are four hours apart. The regular flow of traffic stayed in the 80s, not just short bursts of higher speeds along city freeways. With the stock gearing in my 4 speed auto transmission, the RPMs were around 2,400-2,550. This is a comfortable cruising range. The engine wasn't screaming hard and there was only light engine braking when I let off the gas pedal. The RPMs were relatively low enough to maintain fuel economy (I normally get 22-24 mpg in my 4.6L). I was just outside the drone zone so the noise was minimal. I had lots of good throttle response when I need to speed up and I go right into coast mode when I ease off the pedal. I had the DiabloSport Predator hooked up and it was showing my engine coolant temperature (ECT) was holding at 190*F and the transmission fluid temperature (TFT) was steady at 179*F. This is the ideal cruising speed, I think. I was in the groove. I was in Mustang heaven.
Then I thought to myself, what would it be like if I had 4.10s? Would I be able to cruise *comfortably* at 80-85 MPH? To simulate this, I locked out 4th (OD) gear and slowed down to 70 MPH. The tach was reading right around 3,000-3,100 RPM. According to the gear calculators, this is what it would be like with 4.10s at 80 MPH. I held this for a little over a minute and it felt weird. There was a significant amount of engine braking when I ease off on the pedal. It doesn't go into coast mode until I go below 50 MPH. When I looked at the Predator, I saw the ECT crept up to 197*F. I kinda expected that with the high RPMs. What shocked me was the TFT. It had shot up to 200*F! Whoa! This was not good. I have read just about every 3.73 vs 4.10 thread. Some say it won't hurt to cruise at 3,000 RPM for long periods. I say nay nay! At least not without an auxillary transmission cooler. Everyone has their own opinions of transmission fluid temperature concerns but if you read the tech articles on www.tccoa.com and most popular Ford transmission related websites, you'll see that most of them say going above 200* is not good. (Transmission experts, feel free to post up.)
So, what would I do with 4.10s on the freeway? I would have to stay in the "granny lane" and cruise at 65-68 MPH to keep my RPMs at 2,500. With 3.73s, I would have to cruise at 70-75 MPH. The 18-wheelers and minivans would be passing me and that would suck. I'm not pushing for 3.73s or 4.10s in this post. I just want to share what I found and make auto trans owners aware of a possible transmission temperature issue, and maybe get more inputs from the experts. You read this "Don't fear the gear!" thing a lot. Well, if you don't fear the gear, then at least check your transmission fluid temperature. Your highway driving with 4.10s could be hurting the longevity of the transmission fluid.