Thread: D4 fuel gauge accuracy

Originally Posted by Tombie

Firstly the Tank isn’t parallel so 1/2 isn’t half - isn’t on most vehicles.
Secondly - if you’d stopped on the flat and shut down for a while, when you restarted it would have added a few km.
There’s a hysteresis built in to stop them bouncing around.

The tank is long, thin and runs fore/aft.
Park on the steep angle and it will show a different reading for a while.

Be happy. I smacked the bottom of mine 6 months after I got it, bent the plate and dented the tank damaging the internals.
I go from full to empty on the gauge in 480km...

I think I will investigate this Hysteresis further, I am not sure I understand it fully but think it is a magnetic lag in the sender. Interestingly I parked backwards into the bay with the rear up the hill, would the vehicle react to this in a short time taken to park? When I left the shop after maybe 15 minutes I decided to drive around and then up the driveway to the back of the shop which was up hill instead of entering the busy road.

So the fuel would have been at the front of the tank whilst parked and then at the back as I drove away, how quickly does the gauge react to this? I would have thought the gauge would have stopped when I parked and had this level in memory then slowly adjusted. What happens off road up hill and dale? I wonder how quickly it reacts. I also would have thought there would be a baffle to stop fuel moving quickly in the tank.

Originally Posted by orville

I think I will investigate this Hysteresis further, I am not sure I understand it fully but think it is a magnetic lag in the sender. Interestingly I parked backwards into the bay with the rear up the hill, would the vehicle react to this in a short time taken to park? When I left the shop after maybe 15 minutes I decided to drive around and then up the driveway to the back of the shop which was up hill instead of entering the busy road.

So the fuel would have been at the front of the tank whilst parked and then at the back as I drove away, how quickly does the gauge react to this? I would have thought the gauge would have stopped when I parked and had this level in memory then slowly adjusted. What happens off road up hill and dale? I wonder how quickly it reacts. I also would have thought there would be a baffle to stop fuel moving quickly in the tank.

Resurrecting an old thread.

So about 2 months ago I disconnected the engine battery to install the full second battery kit on my my12 hse. All good from that perspective.

However I now find that the fuel guage is no longer accurate. As an example tonight the needle was near the bottom of the lcd guage, the fuel light low and orange fuel fill light had been on for a couple of days and distance to empty was approx 50k. However I could only squeeze in 49 ltrs, and that was dribbling in at the end to get that much in.

The guage now shows full, average fuel consumption via the readout is 8.2 as per normal and actual is around 10.

Before Xmas I was getting over 70ltrs into the tank when showing low fuel and over 700km to the full tank. Now I'm getting about 500k.

Any idea how to reset this guage? Note there has been no damage to fuel tank.

It's been well documented that one issue with the D4 is the relatively small diesel fuel tank capacity. As I understand it, the fuel system is a closed loop, with excess fuel supplies to the HPFP returned to tank. Therefore in order to keep the pump and system primed (this includes pump seals lubricated), there has to be a residual volume in the tank. I've read that this requires a minimum of 5-8l of diesel. Allowing for variances in use, a factor of safety and things like parking on inclines, this volume would easily increase to over 10l.

It isn't recommended to run any modern car to empty because of the complex fuel systems, especially common rail HP diesel due to risk of damage to fuel pumps etc.

I also agree that the LCD display is sometimes slow to react, but in my experience has always been accurate to within say 5-10%.

Diesel is also less dense than water and is affected by ambient temperature just like any other fuel. There is an allowable tolerance in fuel dispensers of up to 1% according to AS.

My personal experience has been when the gauge reads "empty" the usable volume is exhausted and I'm running into "reserve" capacity, or the fuel needed to prime the system. The closest I've let it go to is 20km to empty, I then managed to get close to 78l in the tank, leaving a theoretical 5l remaining. That in my view is sailing too close to the wind and risks significant fuel system damage. I now fill up as full as possible when the gauge reads empty and normally before the fuel light comes on and I have no issues. On remote trips, minimum 1 x 20l reserve at all times, preferably 2 off.

As to resetting the gauge, a hard reset after parking on a flat level surface after the tank has settled should do the trick

According to my car Manual, you cannot run the D4 to empty. For my information only one day I ran the car till empty ie the computer saying "distance to empty was 0" and the fuel light came on when it said 60kms to empty. However I was able to drive another 25kms after the computer said 0 and then it went into limp mode for 3kms and then the car stopped. I filled up and the computer reset and I drove on.