Vaporisation problem and fitting an Electric Fuel pump to your “D” Series


The Problem.

Since we have owned “Lady Penelope” our Sheerline, she has suffered with acute fuel vaporisation which coincided with the temperature gauge reaching about 180 degrees. Her demeanour became very un-lady like. “Elizabeth” our Princess does not have that problem, the reasons for which are explained below.


I found that the Sheerline engine compartment can become very hot, mainly due to the radiant heat coming from the exhaust manifold and engine pipe. The effect of this radiant heat is that the exhaust manifold side of the engine becomes intolerably hot causing the mechanical fuel pump and the fuel line to heat up. Unlike our DM4 Princess (which has the fuel line on the right hand side of the car, crossing to the left at the front cross member, and has an electric fuel pump about amidships on the chassis), the Sheerline fuel line runs along the chassis on the same side as the exhaust pipe and becomes quite hot and results in pre-heating the fuel. This fuel, in its journey from the fuel tank to the carby, reaches the hot fuel line and very hot fuel pump which is struggling to pump what has now become vapour. This condition is intensified in stop start traffic. If you have just stopped the engine and try to restart – you will find it near impossible to achieve it until things cool down. If you are driving – the engine will starve for fuel and could backfire and will most likely result in the engine stopping very soon.


The Solution.

So, what can we do about this I asked myself? The obvious solution is to reduce the heat at the fuel pump and fuel line. Relocating the fuel line slightly is also a good idea and can be done by undoing the locating clamps on the chassis in the engine bay, moving the fuel line closer to the wheel side of the chassis, turn the clamp around to face the new fuel line position and tighten. A heat shield between the exhaust and fuel line in the engine bay would also help. Check the gasket between fuel pump and engine. It should be a thick gasket providing a degree of insulation between the engine and the fuel pump. Again, one can fit a heat shield between the pump and engine pipe. A good mounting position for a shield would be the top of the engine mount bracket. The carby also gets uncomfortably hot and can do with a thick insulating gasket between it and the manifold if it doesn’t have one.


Although I have suggested the installation of heat shields (made of say 1/8” to 3/16” polished aluminium sheet) I have not done this myself yet. Instead, I decided the quickest thing to do without altering the appearance of the engine bay too much was to fit an electric fuel pump.


There are two fundamentally different types of electric fuel pump. A “sucker” and a “pusher”. Because I was fitting the pump at the rear of the car I naturally used a “pusher”. The local auto electrician sold me a compact fuel pump unit complete with rubber mounts to insulate from any sound made by the pump. I purchased about 1.5 metres of fuel hose and some hose clamps. I already had some automotive wire.


I looked for a good place to mount the fuel pump and decided the rear of the LH battery box was as good a place as any. I removed the LH battery (replacing naturally when the job was finished) then drilled the holes necessary to mount the pump.


Next, I used a mini pipe cutter, to cut the fuel line– and what a gem it was because it made the job clean and easy. I would not suggest using a hacksaw because the filings could enter the fuel line.  I made the cuts in the pipe, removing about 6” of pipe, just before it enters the cruciform part of the chassis and again just rear of the battery box where the chassis begins to flatten out after going over the rear axle,.


I measured, cut with a sharp knife and fitted the hoses to the fuel line going to the pump, clamping them using jubilee clamps. Following the instructions provided, I fitted the hose from fuel tank to the input on the pump and the hose going to the front of the car to the outlet side of the pump.


The electrical wiring. I ran two wires from the pump to the terminal fuse board under the bonnet, in the box. The power was picked up from the Auxiliary Ignition fuse and the Earth from terminal "24" on the board. The pump will not operate if the wires are not connected to the correct terminal nor will it when the ignition switch is OFF.


The last thing I did, although a good idea but not essential, was to fit an “off the shelf” fuel filter. These are cheap as chips and easy to fit. You will be amazed how much rubbish can be in the fuel. The wires and hoses were also tied back to the chassis so they looked a bit neater and didn’t dangle under the car.


I ran the car with the manual pump in-line for about 500 miles and have now bypassed the manual pump totally. I have had no vaporisation problems since, even when the temp gauge was at 190 degrees.


The cost of this conversion is not high and depends mainly on the cost of the fuel pump. It should take less than an hour to fit the pump and do the wiring (or longer if you have a cool ale or two when mates come to see what you are up to).


I hope this helps someone.


Happy and safe motoring

Joe Vavra