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Thread: Towing van with 2016 D4 3.0 - which gear?

  1. #1
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    Towing van with 2016 D4 3.0 - which gear?

    Good afternoon all, and especially the engineers among you:-)
    Towing our nearly 3 ton caravan, I've noticed a curious thing - or at least curious to my non-engineer mind.
    I've tended to tow the van in sport, but noticed even in sport, it would tend to want to change up to 8th gear once cruising. So I started using the flappy paddles to change gear manually. At highway speed of (indicated) 100kmh, in 7th at about 1800 revs, on flat ground, the dashboard fuel use indicator was showing about 15.5 litres per hundred. And the Gap tool was telling me the engine was making around 250nm.
    Change up to 8th, revs dropped to 1500, but torque and fuel use both went UP, to about 350nm and 17 litres respectively.
    Am I right in thinking that using 7th is putting less strain on the transmission, due to putting less torque through it?

    Your analysis is appreciated in advance:-)
    2016 Disco 4 SDV6 SE - LR tank, RWC, Gap IID, UHF, GOE compressor guard, Hema HX1.
    2008 Mercedes E350
    2012 Mercedes 250 CGI Estate (sold)
    2012 L322 TDV8 Luxury (badly missed!)
    2010 RRS 3.0 (sold)
    2007 Audi TT Quattro 3.2 (sold)

  2. #2
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    POWER = RPM x TORQUE

    So raise RPM and you need less torque for the same overall power outcome.

    The engines are designed for this so I’d say it insignificant - higher rpm is more cycles which eventually equals more wear. Less torque is somewhat less strain.

    IMO you’re pulling hairs but Sir Tombie loves a lower gear so ….
    2010 TDV6 3.0L Discovery 4 HSE
    2007 Audi RS4 (B7)

  3. #3
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    Hahaha

    Nothing wrong with dropping the gear one to reduce labouring (and hence EGTs) on the engine.

    I only have a 6sp. So when going through the Pass here I drop a gear and let it wander through.
    I also drive the box through the twisty sections to ensure I’m coming out of curves on pace.

  4. #4
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    Quote Originally Posted by DiscoJeffster View Post
    POWER = RPM x TORQUE

    So raise RPM and you need less torque for the same overall power outcome.

    The engines are designed for this so I’d say it insignificant - higher rpm is more cycles which eventually equals more wear. Less torque is somewhat less strain.

    IMO you’re pulling hairs but Sir Tombie loves a lower gear so ….
    Thanks Jeff, I just got the seat of the pants feeling that the car was happier at the higher revs, was using less fuel, and putting less torque through the gearbox.
    2016 Disco 4 SDV6 SE - LR tank, RWC, Gap IID, UHF, GOE compressor guard, Hema HX1.
    2008 Mercedes E350
    2012 Mercedes 250 CGI Estate (sold)
    2012 L322 TDV8 Luxury (badly missed!)
    2010 RRS 3.0 (sold)
    2007 Audi TT Quattro 3.2 (sold)

  5. #5
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    And based on that I’d say it’s worth raising a gear. Seat of the pants is best
    2010 TDV6 3.0L Discovery 4 HSE
    2007 Audi RS4 (B7)

  6. #6
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    Quote Originally Posted by DiscoJeffster View Post
    And based on that I’d say it’s worth raising a gear. Seat of the pants is best
    Or at least, dropping a gear:-)
    2016 Disco 4 SDV6 SE - LR tank, RWC, Gap IID, UHF, GOE compressor guard, Hema HX1.
    2008 Mercedes E350
    2012 Mercedes 250 CGI Estate (sold)
    2012 L322 TDV8 Luxury (badly missed!)
    2010 RRS 3.0 (sold)
    2007 Audi TT Quattro 3.2 (sold)

  7. #7
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    Quote Originally Posted by GregMilner View Post
    Or at least, dropping a gear:-)
    Yup. Dat!
    2010 TDV6 3.0L Discovery 4 HSE
    2007 Audi RS4 (B7)

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    Quote Originally Posted by GregMilner View Post
    ..putting less torque through the gearbox.
    Same torque at the o/p shaft if travelling at the same speed with the same load regardless of gear but less torque on most of the gear teeth if shafts are spinning faster and less wear on engine bearings, piston skirts etc. It's a balancing act to minimise wear and fuel consumption.
    My TDV8 with 32" tyres uses less fuel ticking over in 8th at 105 kph with our 2.5T van but can use less or more fuel at 100 kph depending on the incidence of undulations. When I fit my 31" tyres the engine should be happier travelling at 100 kph in 8th.
    MY12 RRV 4.4 TDV8 AB, +LLAMS, +e-diff, +ACC stop/go. Produce LLAMS for LR/RR, Jeep GC/Dodge Ram
    VK2HFG and APRS W1 digi

  9. #9
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    Quote Originally Posted by GregMilner View Post
    Thanks Jeff, I just got the seat of the pants feeling that the car was happier at the higher revs, was using less fuel, and putting less torque through the gearbox.
    Yep, I went through this earlier in the year and Tombie's advice was to drop a cog or two and let it rev more. I was already aware of the pitfalls of revs being too low combined with foot further on accel to maintain speed and therefore causing higher exhaust gas temps which is of course a huge no no in diesel land.

    With the recent remap by Cambo, I now tow the 3.0T c/van in 6th or 7th at 2000 to 2400 rpm and approx 90 ish kph. Using Sport mode and manual paddles.
    Rarely venture into 8th unless very flat or slightly downhill.
    Long downhills try to get into 8th asap and let engine coolant/auto oil temps drop which they'll do within a few klms.

    Engine seems to be doing it very happily and easily at 2000 ish.
    Good advice Tombie!
    Before: Ser 2a LWB, Ser 3 S/W, 1979 RR 2 door, 1981 LR Stage 1 V8 (new), 1985 LR 110 V8 County (new), 2009 RRS TDV8
    Now: MY13 D4 TDV6. "E" rear diff. Cambo's magic Engine & Auto Tune.

  10. #10
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    Torque is dependant on speed and Power is a calculated value from both of these. Keeping speed as the constant (i.e. maintaining same road vehicle speed) both power and torque will vary. As said its a balancing act, higher rpm means less torque but more speed. Higher rpm also means more fuel and wear, but, higher engine rpm increases cooling efficiency of the engine (partly negated as these motors run a viscous coupled fan that locks at temperature presents not rpm).

    Makes sense to me to run in a lower gear to increase engine rpm and therefore responsiveness, plus this makes less torque so the engine has less strain, but engine spins faster work harder to maintain speed and you may use more fuel.

    Personally I just let the smarts of the car do this and when towing, it's normally in D. We saw flat 13.0l/100km when crossing the continent from West to East and back again. Never contemplated running in S on thr highway. Sometimes in manual when towing off road.

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