Don’t be afraid of this job, its awkward and at times you need to work in spaces reserved for ‘monkeys hands’ but its possible for an afternoon and quite straight forward for even a beginner to auto-DIY.
First run the vehicle almost dry of fuel, as I have measured the contents, when the fuel reserve lamp just illuminates there is more than 4 gallons in the tank. Chock and Jack the vehicle then support it with the ‘wheels on’ onto ramps or use correct axel stands. Lower and remove the spare wheel.
Use penetrating oil or Plus-Gas to the four 15mm fixing nuts on the tank rim, 2 front and 2 rear. Its good to wire brush these first to remove the scale (and most of the original nut !) as they are going to be corroded. More penetrant or Plus-Gas then leave to soak. Get a pair of sturdy side cutters or piano wire cutters and start to clip/remove the spring wire pipe clips from the fuel feed and return pipes. Once you have done this take a small screwdriver and ease the rubber hose end up from the steel pipes. Spray some WD40 between the rubber hose and pipe, twist the hose and work it upward and off the supply and return pipe stubs. Now reach up and cut off the wire hose clip behind the filler neck on the truck tub. Pull and bend down the rubber filler hose, now cut off the remaining (rusty) spring clip from the vent pipe and pull it off the secondary spigot on the filler neck.
Use a hexagon socket and short extension to break and almost remove all 4 of the supporting 15mm tank nuts. (undo them to the last 3 or 4 turns of thread) Take a screwdriver and drive it between the rear tank flange and chassis mounting cage, the tank should now drop onto the semi-undone nuts, the front lip should not give a problem.
Reach into the gap between the chassis rail and tank by the filler pipe and depress the tiny white tag on the white tank sender unit connector and wiggle the plug free, pull the tank sender cable back over the rear of the axel out of the way by releasing it from the two ‘bendy steel’ clips welded to the tank (often rusted off anyway).
Place a trolley jack and piece of wood under the centre of the tank and take the strain within a couple of pumps of pushing the tank back home. Remove the 4x 15mm tank support nuts fully and then keep them stored safely. Lower the jack about 6 inches and as it descends with tank, rotate it clockwise about 45 degrees, working from where the spare wheel usually resides, guiding the rubber filler pipe around the chassis rail as you continue to lower the tank to the ground. I estimate the weight of tank and reserve fuel to be in the order of 20-25kg so it is manageable on your own, however it is a great benefit to have someone at hand to help drop and remove the tank out from under the vehicle.
Once removed from the vehicle, inspect the first 2 feet of supply and return steel fuel pipe, these are very prone to rust/corrosion in this area and it is an ideal opportunity to cut them back and repair with new copper pipe to at least the gearbox chassis support cross member. This is a good access area to cut and splice in new pipe sections using a short rubber length of hose and clips. Renewing this now is a whole lot easier than when the tank is in place. Just make sure the final position of the fuel pipe stubs is near to original, because the rubber feed and return hoses from the tank are short and cut to size with little margin for error when reconnecting!
With the tank removed remove the sender unit. There used to be 3x 8mm nuts holding this to the tank, these will be rusted to a shape there is no socket on this earth will fit so use a junior hacksaw and cut down the side of all three nuts to make light work of removal. These nuts can be easily removed by rotating/unscrewing them with pliers once ‘side-cut’ with the hacksaw.
Be careful to ease off the thick black rubber triangular gasket with the sender unit as you withdraw it from the tank, the gasket will be stuck to the steel tank with rust, just be careful to ease it free with a screwdriver as you go so that it can be cleaned up and reused. Once the gasket has been cleaned off on both sides and the sender plate cleaned up a film of non-hardening fuel sealant can be used to refit the sender to the new tank. Its worth noting that the sender unit reserve level sensor requires it to be submerged in diesel to function, so testing the sender ‘on the car’ outside of the tank will result in the low level lamp illuminating, regardless of the recorded fuel leveluntil the sender is correctly fitted and submerged below the fuel level.
The final contents of diesel can now be poured into a bucket from the hole left by removing the tank sender. Its a two person job to tip and aim the tank and contents into the bucket. Fuel can then be simply decanted back into the new tank once fitted.
Ensure all vent pipework is transferred to your new tank if it does not come supplied and if you have to remove your old pick up and return unit, remember to cut down the nuts on the old tank just as you did on the sender to ease removal. A handful of 4mm nuts and washers will aid trouble-free fitting of the sender unit and pick up pipe unit. Remember to quickly clean the filter screen of debris on the pick up pipe before refitting.
Replacement is the reverse of removal but it is important to renew any rubber hoses that look suspect or replace hose clamps if they look corroded (as they will !) as any leaks will mean the complete removal of the tank again – and we don’t want that do we!
When decanting the recovered fuel back into the new tank through the filler neck once refitted, you can make a great makeshift fuel funnel by cutting the base of a plastic fuel can and attaching its filler hose, slotting this into the vehicle filler neck. Place some rag across the open funnel to catch any bits or debris that may be present in the reused fuel.
Once fuelled, start the vehicle and check for leaks, drive to the fuel station and initially put in no more than 20 litres of diesel before rechecking your work, if all is well fill up to 50 litres with confidence of a job well done!