Towing uphill at highway speed with overdrive off and the engine reving at 3000 rpm is better than leaving overdrive on and letting the torque converter slip for long periods of time building heat and not bieng able to dissipate it possibly leading to the seals melting and the trans leaking fluid.

I have a proper torque converter (see signature below) so I'd prefer to keep it locked up where possible. If you have such a heavy load that the factory torque converter is continuously slipping for a long duration, I have a feeling it will grenade even sooner if you turn off overdrive and scream along at 3000rpm.

- Chris

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Used to own:
2006 CRD Sport
Suncoast TC, Transgo shift kit, Inmotion, ORM, EHM, Magnaflow SS exhaust, Fumoto valve, EVIC added, Hensley TruControl brake controller, Pirelli Scorpion ATR LR-D in spring/summer/fall, FIA winter front and Blizzaks in winter

The TC unlocks at wide open throttle so the clutches don't burn up.

Torque converter is removed from the power path when the clutches are engaged to lock the converter. This means when the converter is locked it doesn't matter if you have the suncoast one or any other TC. The clutch is doing all the work to push the power to the output shaft.

If you "scream" at 3000rpm with a locked converter you are not harming anything except maybe your hearing. If you unlock and slip like crazy you will generate much more heat, which if not dealt with properly (trans cooler) will quickly degrade the ATF and lead to premature failure of the transmission (this happens only if you rape it enough, but obviously it will give you a TRANS TEMP and go into limp mode the first many times before permanent damage occurs). On top of that, if you have a weak TC and have plenty of slip, it is more likely the TC will die.

http://en.wikipedia.org/wiki/Torque_con ... converters

_________________
L.O.S.T forever!
Silver 2002 Skoda Fabia TDI, 235,000km
Former car: Jeep KJ 2003 CRD

DIESEL - saving millions of liters of petrol every day!

I've done multiple dyno runs with o/d off from 40mph to redline at WOT with the torque converter locked. It stays locked if you roll onto the throttle just right at the beginning. Not to say it isn't slipping, but it's not unlocking.

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05CRD: GDE Hot ECU & TCM tunes, Provent, Cat filter, Facet lift pump, TransGo kit, Florida TC, Samcos, stainless brake lines, HDS thermostat, Renegade light bar,
RL super sliders, Bilstein adjustables, Al's Gen 4.5 Arms, 235/85-16 Duratracs, DTT rear, Elocker front, EVIC+TPMS, Turbo timer, McNally pillar gauges, Weeks Stage II kit.

Only thing to add is doing 3000rpm locked up in third is about 70mph and the torque has already started to drop off.

With overdrive on at the same speed you should be locked up in 5th at 2000rpm sat on the top of the torque curve.

If I can't hold that speed due to the trailer weight or incline then I'll switch overdrive off and reduce speed.

Cheers
Lee

_________________
05 Jeep Liberty (Cherokee in UK) 2.8 CRD Auto Limited
07 Patriot 2.0 CRD 6 Speed Manual Limited.
Fabia 1.9PD TDi (Small VW based car)

Also remember that the torque acting on the wheels is downscaled when you up from 3rd to 5th by 33% because of transmission ratios. Count in the effects of changing gear in the transmission, it will make your precious "real" torque curve very different. The only torque that matters is the one acting on the wheels, not the one acting on the input shaft of the transmission.

_________________
L.O.S.T forever!
Silver 2002 Skoda Fabia TDI, 235,000km
Former car: Jeep KJ 2003 CRD

DIESEL - saving millions of liters of petrol every day!

Hi trac95ker,

Now I follow what you were saying - turn O/D off, and let it lock up in 3rd up the steeper hills? That is exactly what I do on the steeper grades.

- Chris

_________________
Used to own:
2006 CRD Sport
Suncoast TC, Transgo shift kit, Inmotion, ORM, EHM, Magnaflow SS exhaust, Fumoto valve, EVIC added, Hensley TruControl brake controller, Pirelli Scorpion ATR LR-D in spring/summer/fall, FIA winter front and Blizzaks in winter

Yep, exactly why I said if the trailer weight is too high or the incline too steep to maintain 5th lockup then I'll use OD Off to get 3rd Lock up and reduce the speed a little for a bit of mechanical sympathy.

Just saying what's the point of only using 3rd as some have suggested if at the same speed you can cruise in 5th and still be locked up.

Cheers
Lee

_________________
05 Jeep Liberty (Cherokee in UK) 2.8 CRD Auto Limited
07 Patriot 2.0 CRD 6 Speed Manual Limited.
Fabia 1.9PD TDi (Small VW based car)

I tow with O/D on until I come up to a hill. Then I turn it off and turn it back on as I crest the hill. I also use as much momentum as I can to climb the hill.

Ahh my mistake - sorry

I just didn't get it the first go, but to me it sounds reasonable to tow in an OD if the land is flat. In Denmark we aren't allowed to do more than 45MPH with trailers, so I just stay in 3rd with O/D off, it's so simple for me (and I get points on my license if my speed is 20% over the limit ~52ish MPH)

_________________
L.O.S.T forever!
Silver 2002 Skoda Fabia TDI, 235,000km
Former car: Jeep KJ 2003 CRD

DIESEL - saving millions of liters of petrol every day!

At those speeds I would do the same as you and keep overdrive off as you can't legally get 4th lockup anyway.

In the UK we are limited to 50mph on single roads (One lane in either direction), 60mph on dual roads (Two lanes in either direction) and 60mph on Motorways but we can't use the outside lane if three or more lanes are provided. I probably tow around 5mph over the limit when conditions and traffic allow.
Towing Speed limits on the EU mainland are sometimes higher than the UK.

Cheers
Lee

_________________
05 Jeep Liberty (Cherokee in UK) 2.8 CRD Auto Limited
07 Patriot 2.0 CRD 6 Speed Manual Limited.
Fabia 1.9PD TDi (Small VW based car)

Even though the engine can handle towing up a grade in fifth the transmission clutch is probably right at the limit of what it can handle without slipping or is already slipping just a little. Once that happens it's life expectancy is not good. When third is used in lock up the stress on the crappy single disc clutch (which is the weakest link in the drivetrain) is dramatically reduced.

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Manure green 2005 CRD sport4x4, GDE Hot tune, Cat Gut, OE skids, Draw tight hitch, Duramax lift pump, 160K on multiple varieties of fuel, XM radio, Escort live with Redline, fog light mod, GPS, Icom IC7000 all band radio call sign KC9QPF, Grabber AT2s on Soft 8s, FIA grill blanket.

Agree with your post totally but with a little care 4th and 5th is still OK. The engine can only transmit it's maximum output through the TC and TCC whatever gear it's in. A light to medium throttle in 4th or 5th puts the same torque throught the TCC as a light to medium thottle in 3rd. If you meet an incline that requires more then you can manually shift down to third before you overstress the TCC.
It's all about mechanical sympathy, the weight of the trailer and the incline. Any gear can be used on a light enough throttle without stressing the TCC. Full throttle in 3rd and 5th still transmits 295lbft through the TCC, I just change down way before I get to that stage.

Cheers
Lee

_________________
05 Jeep Liberty (Cherokee in UK) 2.8 CRD Auto Limited
07 Patriot 2.0 CRD 6 Speed Manual Limited.
Fabia 1.9PD TDi (Small VW based car)

Oh definitely. The little beast handles normal roads just fine in 5th gear. Although the engine is capable of 295Lbft of torque it almost never experiences even half that much unless under WOT. If a grade is such that it requires WOT to maintain speed in fifth gear then by dropping to 3rd the torque needed is only 2/3 to 1/2 as much to move the same weight only 2/3 to 1/2 the distance with every stroke cycle of the engine. I like the term you used, "mechanical sympathy"

_________________
Manure green 2005 CRD sport4x4, GDE Hot tune, Cat Gut, OE skids, Draw tight hitch, Duramax lift pump, 160K on multiple varieties of fuel, XM radio, Escort live with Redline, fog light mod, GPS, Icom IC7000 all band radio call sign KC9QPF, Grabber AT2s on Soft 8s, FIA grill blanket.