Towing with manual question

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What sort of weight do you intend towing?, the owners manual probably suggests against it but from previous experience it's safe to do so. You'll find the "sweet spot" the car is happy to amble along in working the torque curve.
 
^ sticking to the torque curve is the best way to deal with it. Some people say that towing in overdrive is ill-advised but if Nissan (documentation, not the dealer) give it the ok then go for it - but you need to find that sweet spot.

As an example: the 126kW YD25 engine's torque starts climbing around 1400rpm and finishes its steep climb around the 1900rpm mark. Sitting anywhere from 1800-2000rpm provides the most torque for the least amount of fuel, but you have to balance that with wind resistance - the faster you go, the harder to push through the air and the more fuel you'll use (the dyno NEVER shows how that works!). Staying near the bottom of the envelope is the most efficient and in my car that's around 85km/h (when towing 2.5T, we last returned from Grafton using 17.4LPHK but that was with a faulty turbo boost control solenoid).

Just a note on the torque curve - you don't get a lot more torque on a standard engine above 2000rpm anyway - check the dyno chart below (lifted from dynomotive's web site flogging the Unichip diesel power chip). The torque is basically all done and dusted by 2000rpm and starts to fall away at higher revs (which also means higher road speeds). The horsepower curve (marked "standard power") peaks around 3400rpm with very minor changes through to 3900rpm. You're using serious amounts of fuel at those revs.

The chip (just to highlight what it's doing for the $ invested) has brought a modest increase in torque which peaks only a little earlier and a nice increase in horsepower, with a peak at lower revs than standard. Not moving the peak torque point by much is clever and highly desied, because in top gear those RPM represent a particular road 'cruising' speed that you really want to be sitting around (especially when towing) and making that too low means you're going slower.
 

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I would be towing about 750kgs to a ton. I had just heard in the past the towing in overdrive gears was no good for the gearbox and leads to premature wear and breakdown of the overdrive gear as they are not designed as strong?
Are gears 5 and 6 in the d23 both overdrive gears?
Thanks for your info so far guys, very interesting.
 
I towed 1.7 tonne for 3 years and my daily work trailer is over 1 tonne loaded. Allways towed in fifth, from 70-140kph. Never had an issue yet 95 in fifth was the sweet spot with the van.
 
I would be towing about 750kgs to a ton. I had just heard in the past the towing in overdrive gears was no good for the gearbox and leads to premature wear and breakdown of the overdrive gear as they are not designed as strong?
Are gears 5 and 6 in the d23 both overdrive gears?
Thanks for your info so far guys, very interesting.

that idea is from the old days where the overdrive gear was kinda of an add on to the gear system. they often used weaker gears. idea being use lower gears up the hill and over drive for cruising on the flats.

that really doesn't apply to most newish gearboxes today. probably the last navara you need to be careful with is the D21's.

these days its more about selecting a gear that suits the engine.
 
I would second what tweak'e wrote. most 5 speed manual boxes were an evolution of earlier 4 speed ones. 5th gear was generally not even in the same part of the gearbox as the rest. To take the older Nissan boxes as a typical example, gear 1-2-3 are in the main housing of the gearbox, fourth gear is not actually a gear at all, just a sleeve that coupled the input and output shafts together and so is by far the "Strongest" as there are no forces trying to drive the gears apart or laterally up and down the length of the box. That is where the old "Tow in fourth" advice originates. Reverse gear was out in an extension housing on the other side of the main bearing support plate. Reverse is a lot weaker than the forward gears.

Most 5 speed boxes just enlarged the extension housing, lengthened the mainshaft and added another gear out there, supported by a smaller bearing and thinner housing than the lower gears. I would hope modern 6 speed boxes have all the forward gears inside the main housing.

When towing my my old D22 I used to gear down any time that it dropped below about 2500RPM under load. Where you want to change depends on what your intent is. I towed as if I wanted to make good time and I paid for it at the pump. Otherwise you can allow lower revs and more sedate progress to save money at the pump but pay for it in travel time.

IMO if you want good progress you want to keep the average RPM under load somewhere in the middle between peak power and peak torque. When cruising on the flat you simply want the highest gear it will comfortably pull. By comfortably I mean not allowing it to lug and fizzle and sound like an old TB42 Patrol.
 
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I regularly tow race cars to and from sydney.

When the truck was stock, and when I got my exhaust I pritty much always towed in 5th when towing above 2T.

Now the truck is tuned it doesnt matter so much, it hardly labours so it gets 6th gear a lot more.

Generally I get 12-14L/100kms towing at 100-110km/h.
 

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