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Originally Posted by Hunner
My experience with this is that when the torque convertor is locked up but in overdrive with our I5 engines when you lug it on hills or pulling its making the engine work harder. Too tall gearing and not enough power. If you are in 3rd fluid drive or locked the higher rpms are letting it breath better, it has more torque output and circulates coolant more rapidly for better heat exchange. That's my story and Im stickin toit! My Cummins diesel long stroke 6 cylinder does that and it lowers the EGT's by a bunch if Im on long grades. Aluminum melts at somewhere around 1300 degrees I believe! I have a triple lock torque convertor after I blew the stock one and a modified tranny with modifed valve body to do all this. I also added straight cut gears to the over drive. What Im getting at with this is You might want to tow in 3rd if you are having this occur in a Hummer H3.
By the way you are about to run out of gas!
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May I add some clarity, it took me a few readings to understand?. At low engine rpm's the friction internal to the torque converter increases heat in the trans and fluid; as rpms increase, the heat reduces. This is due to more circulation, and due to less friction; so a double benefit. Therefore, with the trans in third gear, the rpms are increased, so there is less friction and less heat.
Also, if the speed in third gear exceeds approximately 65-70 mph, the torque converter will lock.
Your fuel mileage will go down....
I believe they do recommend towing in third gear, especially if running in the mountains.