towing in 5th

[rastas dog]

Hi guys have read a few times that you shouldn't tow in 5th.
What's the deal? What are these guy's on about?

Cheers Gav

 

[Old.Tony]

They're worried about straining the engine.

In the auto, it will unlock the torque converter and kick back when it needs to - the engine measures the load and knows when it's too much.

However, on hills it's a different story. We've learned that on steep inclines, allowing the speed to bleed off and slowly down-shifting until you're in 1st gear is far better on the engine (temperature-wise) than trying to flog the thing into making it over the top before it blows a gasket.

We've done a little towing with ours (somewhere in the 50-55K ballpark now) and generally ALWAYS have the gear selector in "D" with overdrive OFF (so that a large "D" is displayed on the dash). Have only overheated when we didn't change down for the hills.

Fuel consumption dramatically increases in lower gears. Maintaining 95km/h (the sweet spot, 2,000rpm, for our engines in top gear) we use somewhere around 15 litres of diesel per hour (this is an instantaneous flow figure you can get from the ECU using diagnostic tools). When we're in 4th gear, this rises to around 28 LPH (not LPHK = litres per hundred km, but LPH = litres per hour). In 3rd gear we don't try going that fast because we'd be hitting 50LPH and I don't feel like donating to Shell/Caltex/Mobil any more than I have to.

As it is, in 1st gear up through Cunninghams Gap at 20km/h we were still using around 16LPH - in economy figures that's around 80LPHK for the climb, but the temps were good so no engine worries.

 

[bods]

^^not only that tony, but some of the older patrols and navs (even hiluxes too I believe) had problems with actually stripping the 5th gear in the gearbox. People believed this was because of excessive load on the gearset that it wasn't designed for. Some people on the patrol forum had issues without even towing so they can't say for certain it was the towing that caused it or some sort of manufacturing defect that caused it...

In any case, it is recommended not to tow in "overdrive" which is what 5th gear is in 5 speed cars, I think it may actually be 5th and 6th in manual d40's, but I'm not certain on that...

 

[Old.Tony]

You have it right, 5th in the auto and 6th in the manual = overdrive.

Experience tells me there's not much troubling the D40 pulling 1.8T (well, it might be closer to 2T but I'm not saying that to anyone, especially someone who might have seen the compliance plate and who might work for RMS). We've taken it UP the Alpine Way, up Mt Ousley, up Mt Victoria, up Cunninghams Gap, up Moonbi, Nowlands Gap ... and it's always in lower gear when doing the heavy stuff.

When the going gets a little hard it always kicks back. The only time it hasn't done that was in the stretch of road between Kulgera and Erldunda in the NT - it seems that above 125km/h, despite towing the caravan (as pictured below, the shot was taken less than 48 hours after we did this) the car is quite reluctant to disengage the torque converter clutch and will happily steam up and over hills nudging 130km/h without overheating - and that's on a 40C+ day.

 

[kernels]

In the manual geabox, 5th gear is a 1:1 ratio, this means that the gearbox input and output shafts are locked together and no side loading is applied to the gearbox (usually).

This would usually then make 5th gear a good gear for towing, unless there is something weak in the Nav gearbox when it locks the two shafts together.

In the end, you really want to keep your diesel revving at peak torque (around 2k rpm) when towing, this is where it will tow the 'easiest' and also use the least fuel.

As an aside, guys with worn manual gearboxes will also usually find that 5th gear is the quietest because of the lack of side loading.

 

[rastas dog]

So basically it's just when the engine starts to labour change down instead of planting your foot in top gear. (common sense)

 

[kernels]

So basically it's just when the engine starts to labour change down instead of planting your foot in top gear. (common sense)

Exactly

 

[rastas dog]

Thanks guys

 

[Eug]

does that mean it should be okay towing in 6th sitting at 2000 rpm? how much strain is there on the drivetrain once the vehicle/trailer has momentum?

 

[kernels]

does that mean it should be okay towing in 6th sitting at 2000 rpm? how much strain is there on the drivetrain once the vehicle/trailer has momentum?

Nothing wrong with towing in 6th in the right conditions, it's all about keeping the engine in it's happy torque range.

For daily driving, towing or just dropping the ankle biter off, I try to keep the engine between 1500 and 2500 rpm. Every now and then on the motorway onramp I will revv it out through the gears just to clear out the system a bit. I try to never let the engine work hard. As Tony said above, it's better to be at a lower speed with the engine revving in it's happy zone all the time.

 

[Old.Tony]

I'm going to add something about hillclimbing and accelerating specifically in automatics here too.

Our torque converters have a stall speed somewhere in the region of 2700-3100rpm. That's too high - 2400rpm would have been more ideal, and Wholesale Automatics sell one that does just that.

Given the stall speed though, I did some testing on acceleration and fuel consumption rates and discovered that I use MORE fuel keeping the RPM around 2,000 than I do keeping it between 2500-3000rpm.

It then makes sense that because we're near the stall speed, the engine has more 'grip' on the drive shaft and is thus transferring more engine power through the drive train rather than losing it to slippage in the torque converter. It then makes sense that hillclimbs should be performed (with a standard TC) by keeping the RPM somewhere in the 2500-3000 range.

We did exactly that climbing Cunninghams' Gap with the van as we headed to the Muster and the engine load was kept light, the coolant temp stayed normal, and the car didn't feel strained in any way.

 

[happy john]

Just to ad to tony's comment going back to manual being a navara owner since 89 i have always towed in 5th always got over 200k out of the 4 i have owned never a problem but i keep it in it's torque zone if i start to labour i go back a gear listen to your motor.

 

[wes570]

so in a manual that is the torque zone on a 03 d22?

 

[Old.Tony]

so in a manual that is the torque zone on a 03 d22?

Not in a D22, Wes (this is the D40 Drive Train forum). I think your "sweet spot" is closer to 3,000rpm (where the torque curve has finished climbing rapidly and starts to level out). Different final drive ratios because of the different horsepower.

 

[kernels]

I paid a bit more attention while driving my manual yesterday and will amend my previous figures. I drive mostly between 2000 and 3000rpm, I don't let it fall below 2000rpm unless i'm coasting downhill.

When I'm sitting at indicated 110km/h on the motorway, it's revving just over 2000rpm in 6th gear.

In the autos it sounds like you have to keep it revving a bit higher, more towards 3000 rpm because you really want your torque converter to be locked for fuel economy. (Exactly as Tony said)

 

[wes570]

Not in a D22, Wes (this is the D40 Drive Train forum). I think your "sweet spot" is closer to 3,000rpm (where the torque curve has finished climbing rapidly and starts to level out). Different final drive ratios because of the different horsepower.

sorry I didn't read the top. but thanks tony for that info.