Leave it off. 4th gear is not really for towing. Besides, with OD off you still get lock-up.
I was under the impression that if it's hunting gears (down shifting on and off) while towing the constant switch generates heat every time , this occurring repeatedly doesn't allow the fluid to cool fast enough thereby causes the heat which kills the tranny.
If There's lock-up with it on and it holds it on flat to fairly flat terrain, not safe?
1994 Hunter Green ZJ 5.2L Quadratrac
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I don't tow or haul anything besides a stuck fellow beach wheeler. Should I keep it off while daily driving? Never really understood OD. I've had it on for the past 2 years since is owned it...better to keep it off?
04 WJ: 4" IRO, Front Adjustable IRO Arms, Bilstein 5125, JKS Trackbar, 265/75 R16 Grabber AT2, OBA
I've towed all over with heavy azz boats (5000+) and can talk about highway towing all day. OD-off essentially keeps you from having to monitor the final drive ratio being used or not.
So if you want to make the best mileage possible while towing (and you are dilligent), leave OD on and monitor the terrian for the need to turn OD off when the speed you are doing drops due to terrain changes. "Monitoring" means turn off OD before the uphill portion and put it back on for the down hill and leave on for level terrain.
The problem with this is that you need to have a LOT of time with towing the load of the same weight and carefully observe the tach for when it "slips" from final drive or actually changes gear from final drive. When it slips from final drive you'll know it when the RPMs increase by about 500 ...but there was no gear change. Once terrian levels back out, the rpm drops right back to where you were.
It's correct operation but it builds up heat when it has to slip (read shear fluid and increase pressure) in order to maintain speed. If you leave OD on, no matter the terrain, the trans will do this all day for you and get hotter than it needs to.
The alternative to constantly monitoring the terrian for when the trans needs more gear is to turn OD off & leave it off. It does sacrifice MPg on the level but the trans is not going to have to slip or even downshift to maintain speed. The engine is fine to run all day at 3K as long as all else is happy and maintained.
What you should do? If you tow the same load over the same terrian often, you'll know when to turn off OD and when you can leave it on. If driving is mixed (highway/city) leave it off. For example on the way to the lake, I know the path and the terrain, so the 15 mile highway portion has only two areas that I need to turn OD off until it levels out. The rest, I leave it on till I exit.
If I don't know the terrain, i leave it on for level portions that I can see are level, then off for traffic and inclines.
If you leave OD on and fail to realize a hill is coming and it slips to maintain speed or even downshifts you're not going to kill it but the more you fail to realize and are not dilligent, the more life you're sacrificing from the trans.
2000 Laredo 4.7L Selec-Trac. 177K miles, Leather, 245 tires, tow package, crappy CD changer, full size spare, roof cross-rails & sunroof. Changes & fixes: Rear Addco sway bar & greasble bushings, upgraded headlights, upgraded tail lights, new hood struts (replaced 2X), new rear hatchglass struts, new radiator (replaced 3X), new oil pressure sending unit (replaced 4X), 2 new speed sensors, 2 new door lock actuators, new ignition key cylinder, chrome front tow hooks, Mobil 1 Synthetic 5/30, Purolator Pure One oil filter, EBC slotted & dimpled rotors, EBC Greenstuff pads, new front shocks (replaced 3X), new rear shocks (replaced 2X), new IRO steering stabilizer, new timing chain cover, new water pump, thermostat, new thermostat housing, new high pressure power steering hose, Michelin-X radials, new sunroof assembly, new single-piece lug nuts, new exhaust manifold studs & gasket on driver's side, new Durango alternator. Jeepforum.com sticker, Visit cobaltboatsforum.com when you can!