Why a 62 mph limit in Third Gear in a Frontier

[Boomer]

General question. I descended a very steep mountain yesterday in PA in my 2007 V-6 Nissan Frontier auto trans. To control my speed, I went into third gear on the auto trans. Held me back but I got a whiff of hot ATF. Out of curiousity, I looked in the owners manual when I got home and it said never go faster than 62 mph in this gear. Now I was right at that speed and my rpms never went over 3000. What gives with this?

 

[Colt45ws]

Generates excess heat.

 

[Boomer]

I gathered that but I have never had an auto trans before that did that. RPM was always the limiting factor. What is different??

 

[JTK]

Maybe this particular Jatco 4spd (or 5??) auto doesn't lock the torque converter in 3rd (like some 4sd ATs will). Like Onmo' says, that would generate lots-o heat.

Joel

 

[Boomer]

JTK, that makes sense. I just never had an auto that wasn't RPM governed. However, they tell you to take it out of overdrive with a button on the gear selector. Apparently this must drop it down to fourth gear with the TC locked.

 

[Colt45ws]

Yeah, if the TC is not locked it will slip a lot. Its feeding torque the reverse of normal (into the engine). I cant imagine thats a very efficient mode of operation for it, which means HEAT.