Anyone run an overdrive on their TD5 Defender?

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Originally posted by JDNSW
I would be very surprised if overdrive on a diesel had a significant effect on fuel economy without your changing driving style. Let's look at it objectively. You fit an overdrive, and it reduces the engine rpm at cruising speed. It does nothing for the amount of power required - this is the same.

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Having spoken directly to a bloke who has fitted the GKN unit to his 90 Td5 - this is absolutely the case. He's consistently getting mid 8's on his way between Sydney and Melbourne every week. I understand where you are trying to go with this and I also understand the basic difference between a modern diesel's consumption and a petrol's - but his wallet is apparently telling the story. He used to average just over 10L/100km on the same trip.... week in, week out. He is trying to maintain the same road speed in his comparisons - well... as much as the absence of cruise control will allow. He is not approaching it in a really scientific manner such as running it on a dyno for an extended series of tests - but is rather doing the distance and filling to the top (as we all do) to see what his consumption was. Maybe the difference in fan spped is more significant than you reckon. I know mine holds me back after a high-speed run - where I try to accelerate back to cruising speed I can hear the fan wailing loudly as the clutch forces it to spin at engine speed for a while.

B. Davis does indicate that fuel consumption drops - and I'm not sure that reputations are easily kept in Australia if you outright lie about your product as the average Aussie psyche loves to see people cut down over small things.... so people like this have to be careful in what they promise. I'm not trying to defend him in any way - I don't have any personal interest in his company, but unless anyone knows any different through personal experience I have to believe him.

Omaroo here is the text from the website re price of the unit:

GKN Land Rover Overdive for a limited period is available for £799 plus vat,[whilst stocks last] we would be please to fit the Overdrive for you in our workshops - please call for price, curtosey vehicle available whilst your fitment takes place.
Place you order now, whilst we have stock 01769 550900

From www.devon4x4.com, am pretty sure this is the right unit.
Thats $1938.00 plus shipping plus import duty (import duty and shipping surely are not worth $2000.00??) - am fairly sure fitting these units up is also not too difficult.

If the economy improved that would be a bonus - intend to do a lot of touring in the vehicle and would like to be able to do so without the engine screaming its head off - if this can be achived with the gearset mod mentioned I may follow this route.

<div class='quotetop'>QUOTE</div><div class='quotemain'>The only time that a diesel uses significantly more fuel per horsepower is when they are overfuelling to get the last few horsepower for that rpm - but this does not happen with modern diesels like the TD5.[/b][/quote]

I think this exactly explains Tombraider's 15l/100km with his remapped ECU. It is why I am also interested in the EGTs from any overfuelling.

But you would have to think that a considerable drop in cruising rpm (and therefore fueling) would also have a big impact on consumption. :?

<div class='quotetop'>QUOTE</div><div class='quotemain'>intend to do a lot of touring in the vehicle and would like to be able to do so without the engine screaming its head off - if this can be achived with the gearset mod mentioned I may follow this route.[/b][/quote]

Might be worth also considering a noise deadening kit. Pretty sure some people here have invested in them. Might be worth dropping a PM to 'rmp'.

I've just had the 1.2Q gears fitted. Haven't been far on the open road yet to determine any difference in consumption.

But it is so much quieter its not funny. Instantly noticable. Well worth it.

Regards
Max P

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Originally posted by dhumphri
Omaroo here is the text from the website re price of the unit:

GKN Land Rover Overdive for a limited period is available for £799 plus vat,[whilst stocks last] we would be please to fit the Overdrive for you in our workshops - please call for price, curtosey vehicle available whilst your fitment takes place.
Place you order now, whilst we have stock 01769 550900

From www.devon4x4.com, am pretty sure this is the right unit.
Thats $1938.00 plus shipping plus import duty (import duty and shipping surely are not worth $2000.00??) - am fairly sure fitting these units up is also not too difficult.

If the economy improved that would be a bonus - intend to do a lot of touring in the vehicle and would like to be able to do so without the engine screaming its head off - if this can be achived with the gearset mod mentioned I may follow this route.

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AU$2,287 including VAT. Would we need to pay that if we are having it exported?

You should not have to pay VAT, but the boys at Customs might want to hit you with a duty as it comes in. :wink: I think anything over $800 is meant to be dutyable??? :?

Tusker where did you source the transfer case gears and how expensive was the whole job if you don't mind me asking. Daz

A secondary effect that I did not consider is that unless you change down, the overdrive effectively limits the available power (and hence fuel consumption), although the effect of this will be very dependent on road conditions. For example, on the Newell Highway (straight and flat) I would expect no effect, whereas on the New England (hilly and bendy), a lot.
Most drivers would not bother to change down, but would put up with slower acceleration out of curves and accept slowing a bit on hills rather than change down.

My comment about modern diesels not overfuelling does not necessarily apply to one with remapped engine controls, although in most cases they will also have increased boost so specific fuel consumption will not have changed much. But if additional power is there it tends to be used, particularly by those types that go to the expense of doing it in the first place, and this additional power shows up on the fuel bill (and usually on brake wear as well).

Whilst mine isn't a Td5, it is a 200Tdi, I did a similar thing to it.

The transfer case gears where stuffed after a trip through the Oodnadatta, so I replaced the gears with Maxi-Drive reduction and Disco high-range. I sourced all of the parts from Maxi-Drive costing around $3,200.

It did make a big difference, however up here in the NT I found that my fuel consumption went through the roof. But speeds of up to 140km/h where easily reached. I also did find though, that 5th gear is now definetely only an overdrive gear - it basically has no pulling power at all.

When I relocated it down to Tassie, where the speed limits apply - the fuel consumption was down to around 8.5 - 9 litres per 100km's. That is driven fairly hard in places - as it isn't exactly flat! I really don't use 5th gear that much unless I'm on the highways, as it's a waste of time engagin under 90km/h.

Personally, I'd recommend this course of action over an overdrive unit - because basically you get the best of both worlds. I now have a vehicle that crawls slower than a baby, and one that also cruises quite comfortably, and a lot quieter.


Cheers
Chris

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Originally posted by Noddy
You should not have to pay VAT, but the boys at Customs might want to hit you with a duty as it comes in. :wink: I think anything over $800 is meant to be dutyable??? :?

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You will have to pay import duty not sure what it is these days, probably about 15%, and GST at 10% on the price plus import duty.

You can get away without them for costs below some figure - I have seen the $800, but you won't for the price we are talking about. It may be worth asking a customs agent about bylaw entry - this used to apply for goods not available here, but I don't know if it still applies. And you would still have to pay GST.