D4 Long Range tanks and fuel usage?

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Originally Posted by ramblingboy42

I'm really surprised the manufacturer of the long range tank couldn't at least have designed it to give you a reasonably accurate fuel level on your gauge

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The problem is that there isn't a gauge in the long range tank - only the factory gauge and factory tank - the long range tank keeps the factory tank full until it's empty the you have the remaining full factory tank to go - the computer can't make the calculation as it has no idea there's fuel flowing into it keeping it full.

That's my understanding of the system in these and how it was describer to me - was on a road trip in a friends and the gauge didn't move off full until we were half way through NSW (Starting in Melbourne).

ahhhh , I see, its not a replacement tank but an extra one......

My long range tank is seperate and you have to pump from it into the main tank, so i have fount in this situation its very handy as you know when the long range tank is empty and exactly what you have in the main tank.

As for the computer , well its usually close as it still reads from the standard tank ,the distance to empty is a totally different thing as it gets very confused when you keep driving and the tank becomes full again after pumping it from the L/R tank .

Bulletman

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Originally Posted by Tombie

Nope!

You have the gravity fed tank I take it?

The computer can’t work it out.

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I suppose the only way to find out just how far a tank will get me is to ...
1. Fill the tank completely
2. Reset the trip meter/ fuel usage
3. Drive until I get a 'low fuel' warning
4. Stop ... and drain the remaining fuel from the tank to see just how much is remaining

If I ensure that there is some fuel in reserve, say 6L out of the remaining fuel, then hopefully I can get an idea of what range I should be able to get out of the remaining fuel.
If I add the indicated mileage/fuel usage to the remaining mileage/fuel usage (less the safety reserve) I should be able to get at least some sort of indication as to what distance I should be able to get from a full tank .. as long as driving conditions don't vary too greatly.

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Originally Posted by Homestar

The problem is that there isn't a gauge in the long range tank - only the factory gauge and factory tank - the long range tank keeps the factory tank full until it's empty the you have the remaining full factory tank to go - the computer can't make the calculation as it has no idea there's fuel flowing into it keeping it full.

That's my understanding of the system in these and how it was describer to me - was on a road trip in a friends and the gauge didn't move off full until we were half way through NSW (Starting in Melbourne).

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Yeah ... that's what I expected to happen ... and it did.
The gauge sat there showing full but eventually started decreasing.
It started decreasing earlier than I expected though. I thought I would get to around 1200km before it started to reduce .. but it started at around 850-900km
Regardless of what is being indicated, it seems like the fuel usage figures are greatly inflated .. probably for marketing reasons ... which seems to smack of the old Volkswagon exhaust tampering issue.
I would have thought that there would be an in-line type of 'flow metering' that the vehicle 'smarts' used to determine 'actual' fuel usage which SHOULD give the driver a pretty reliable idea of what the actual range is likely to be .. regardless of the size of tank or feed mechanism.

As I keep explaining -

(1) The fuel economy is based on lab cycle testing and only for comparison purposes. No VW Style conspiracy involved.

(2) The consumption figure is a moving average - not an average of the tank since last fill.

(3) You can improve its forecast using IID

(4) inline flow meters aren’t used… injector volume x duration is calculated

(5) range calculation is again a moving average - think about it - a flow meter doesn’t know how much it’s going to flow - so how could it calculate range based on that equation. It can only assume based on a known volume and extrapolate from there.


As for your predicament, even though the filler was “full” how much did you manage to put in?
Not unheard of to have a big airlock in the auxiliary.

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Originally Posted by rapserv

I suppose the only way to find out just how far a tank will get me is to ...
1. Fill the tank completely
2. Reset the trip meter/ fuel usage
3. Drive until I get a 'low fuel' warning
4. Stop ... and drain the remaining fuel from the tank to see just how much is remaining

If I ensure that there is some fuel in reserve, say 6L out of the remaining fuel, then hopefully I can get an idea of what range I should be able to get out of the remaining fuel.
If I add the indicated mileage/fuel usage to the remaining mileage/fuel usage (less the safety reserve) I should be able to get at least some sort of indication as to what distance I should be able to get from a full tank .. as long as driving conditions don't vary too greatly.

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Suggest you keep a spreadsheet of usage. I base my usage on the surface that I've mainly travelled on per tank full so I know what I can expect out of a tank for that surface.Attachment 170289Attachment 170290

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Originally Posted by rapserv

I would have thought that there would be an in-line type of 'flow metering' that the vehicle 'smarts' used to determine 'actual' fuel usage which SHOULD give the driver a pretty reliable idea of what the actual range is likely to be .. regardless of the size of tank or feed mechanism.

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Having built one of these for marine diesels you have two sources of error. One is the error on the flow-meter from the tank to the pump, the second is on the flow meter from the return to the tank and that needs accurate temperature compensation also. Frankly unless you pay a *lot* for, and accurately calibrate your flow meters the current method of estimating the injected quantity is far more accurate. The issue with the current method of estimating the injected quantity is Land Rover are really **** at it. The ECU knows pretty much *exactly* how much fuel it's injecting. The trip computer doesn't seem to have access to, or use that information.

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Originally Posted by rocket rod

Suggest you keep a spreadsheet of usage. I base my usage on the surface that I've mainly travelled on per tank full so I know what I can expect out of a tank for that surface.Attachment 170289Attachment 170290

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.. sounds like a good idea to me!

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Originally Posted by BradC

Having built one of these for marine diesels you have two sources of error. One is the error on the flow-meter from the tank to the pump, the second is on the flow meter from the return to the tank and that needs accurate temperature compensation also. Frankly unless you pay a *lot* for, and accurately calibrate your flow meters the current method of estimating the injected quantity is far more accurate. The issue with the current method of estimating the injected quantity is Land Rover are really **** at it. The ECU knows pretty much *exactly* how much fuel it's injecting. The trip computer doesn't seem to have access to, or use that information.

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.. that's what seems to be the issue to me as well.
LR are not adequately using the available real time data .