I recently returned from a two week road trip to Colorado pulling a 2,000 pound 6x12 enclosed cargo trailer. I used tow/haul mode a little bit and noticed something I can't quite put my finger on.

When pulling up hill, the rpm's would jump a couple hundred revs but the transmission gear indicator didn't indicate a down shift. Would this be the torque converter unlocking? If so, why would that affect the rpm? I assume it was okay to drive it like this but I typically went out of tow/haul mode and just used select shift to drop the tranny down a gear so I knew what was going on.

The truck needed about 80% throttle in third gear to maintain 50 mph going up an 8,000 foot pass. I imagine a 5,000 pound load would require 2nd gear. This with the 5.0. Maybe this is normal and I know at 8,000 feet you are losing 25% but I was surprised by this.

NC

 

Yes, that's simply the TC unlocking. Slippage = rpm rise = HEAT.

The 5.0 is not the best engine to tow with at high altitudes. This is where the EB shines.

 

So unlocking prevents slippage which would be a good thing if I understand you correctly. So the unlocking does cause the revs to rise or are you saying the revs rising were a result of slipping? I doubt it is the latter as it was a deliberate change when tow/haul was activated.

Thanks.

Greg

 

When the TC unlocks, there is slippage by design. This slippage generates heat. The goal when towing is to keep the TC locked as much as possible. If it won't lock due to load, you are better off in lower gears.

 

This confirms what I suspected. But what doesn't make sense is why would tow/haul mode intentionally cause this to happen when unlocking the torque converter generates heat? It seems counterproductive. Now if tow/haul mode unlocks the torque converter to prevent constant locking/unlocking that makes a little more sense.

Greg

 

Tow/haul is supposed to try to keep it locked as much as possible. What you need is an accurate transmission temperature gauge.

 

Are you sure you had tow/haul ON? My 2012 goes from 6th locked to 5th locked when tow/haul is on. It has NEVER unlocked in 6th.

 

I would not worry too much about torque converter lock/unlock when towing. The trans cooling system is designed to keep fluid in an acceptable temperature range. Until automatic overdrive, Ford 3 speed automatics had no lockup clutch so all converters had a hydraulic slippage of about 3%. However, if you are in a hard pull at very low speeds, trans fluid will heat up!

 

The less heat the better no matter what you are towing. Keep it locked as much as possible. My truck doesn't have tow/haul mode, it just has OD off. When pulling on the interstate and a hill is coming up that I know the TC will unlock, I always hit OD off and let it lock in 3rd before it tries to unlock. Lower gear, TC locked, less heat, longer tranny life.