Start by removing the fuel tank. Next, remove the petrol gauge sending unit. Take a look inside the hole for the sending unit to verify the condition of the lining of your tank. Do this outdoors using sunlight for illumination, not a flashlight or your cigarette lighter, for obvious reasons. If the lining of your tank is shiny, you’re in luck, because that is the way it is supposed to look — if not, most old car petrol tanks can be cleaned and repaired.
If you live near a metal stripper, take your tank there and have it stripped. It will come back looking like new and can save you hours of work. Another possibility is to take your tank ¨to a radiator shop to have it hot tanked to clean it, and then also solder any holes. But if you don’t want to do that, you can clean your tank at home.
To clean your tank, duct tape the sending unit opening to seal it, then pour in a one pound coffee can of old screws, nuts and bolts. Now add a couple of quarts of water and slosh this mixture around to loosen rust. Be sure to agitate the tank vigorously and go over its inner surfaces completely. Pour out the mixture and repeat the process until the water comes out clean.
When you have your tank clean, check it for leaks. Fill it up so the water rises into the filler neck. Use a grease pencil to circle the leaks ¨you find. Look for wet or rusty patches. Don’t forget to check around the filler neck weld ¨too. Any holes can easily be soldered up at a radiator shop.
Never try to solder leaks yourself, though. Even after sloshing it out with water, your tank ¨will contain explosive fumes, and its inner surface will be permeated with petrol that could be dangerous.
If you only have a few tiny leaks, you can seal them with a petrol tank sealer and restorer kit. These are available from auto spares sources. Just make sure you get a sealant that is alcohol resistant. Spiked fuel could wreak havoc with your fuel system if you don’t. After cleaning the tank as thoroughly as possible, let it dry then, with the openings sealed up, slosh the sealer solution around so you coat every surface. Pour out the excess, let the tank dry for a day and then give it another coat. Let the tank cure for a week with the orifices open before installing it on your car.
Replacing the tubing
Here are a few unseen upgrades I make to any classic I drive. Most people don’t bother replacing fuel lines when they refurbish or replace their fuel tank, but it is a good idea. I have actually had a fuel line rust through and develop a tiny leak. The effect it produced was that of a defective fuel pump. The car would go just fine and then the engine would stop. Then it would sometimes restart and run for a while and stop again.
Suffice it to say, it was very difficult to diagnose the problem, but it could have been worse. Fuel could have dripped out of the corroded line and caused a fire. So now when I restore a petrol tank I always replace the fuel line, and while I’m at it I add a few upgrades.
Most old cars have mechanical fuel pumps. They are reliable, but I install an auxiliary electric pump in the back near the petrol tank as well. That’s because when an old car has been sitting, the fuel in the carburettor float bowl evaporates out. Then when you start it, the mechanical pump only gives a little squirt each time the engine turns over, so it takes a while to fill up the float bowl and fire the engine. But with an auxiliary pump and a toggle switch concealed under the dash, you can fill the carb quickly using very little juice from the battery.
Also, some old cars are prone to vapour-lock on hot days. That’s when the fuel gets so hot in the mechanical pump, carburettor or fuel lines that it vaporises and renders the mechanical pump ineffective. With an auxiliary electric pump, you can just actuate it from a switch on the dash and push the fuel on through.
Electric fuel pumps are available for both six and 12-volt systems and can be fitted inside the frame of the car where even the most persnickety car show judge won’t find them. You can also add a modern fuel filter between the pump and the tank.
Valves and flares
Another trick I like is to put a shutoff valve in the fuel line where it can’t be spotted. That way if I am on a trip and have to leave the car out for the night I can just switch off the fuel. A thief can start the car, but won’t get far on what is in the carb.
Buy steel tubing in the diameter that is correct for your car, along with the correct fittings. You can get the tubing in rolls. Use a tubing bender to bend the tubing without crushing it, and flare the ends of the lines using a flaring tool.
To make a proper flare, cut the end of the tubing off square using a tubing cutter, then file away any burrs. Clean the inner and outer edges of the cut too, so you have a nice, round edge that will seal well. Put the tubing in the flaring tool, oil the end of the tubing, then tighten the tool evenly to make a flare. If it comes out crooked, cut the tubing off and try again.
With your tank repaired or replaced, with an auxiliary fuel pump and new tubing, you can kiss fuel delivery problems goodbye.
The little upgrades suggested can easily be concealed, and can make your classic easier ¨to start and more fun to drive. And if your ¨stock mechanical fuel pump ever fails, you can always flip on the spare electrical one to get ¨you home.
Restoring the sender unit
If you are unsure as to whether your petrol tank’s sending unit is in good order, connect it to a multi-meter set to ohms and move its actuating lever through its range. The gauge should go up and down smoothly. If it does not, check your contacts and try again. If you still get no response, the rheostat inside is probably dirty or defective.
If your sending unit has one of the more modern plastic or brass floats in it, hold the float next to your ear and shake it. If you hear rattling, the float is leaking. Also, if it has any petrol in it, replace it. Small plastic medicine bottles work well for this job.
This old tank from an estate wagon has been patched before and is leaking again. Time to replace it |  |
Luckily a new tank was available for our car |  |
To fix small leaks there is a three-part sealer available that works very well and will hold up for years |  |
To test your tank’s sending unit, hook up a multi-meter and set it to ohms. The unit should read correspondingly |  |
Shake an old float to see if it rattles. If so, replace it. Also replace it if it has fuel inside |  |
Bend fuel line using a tubing bender. Gentle bends can be done freehand |  |
Make sure you install the pump facing the right way, and add a ground strap too |  |
Fuel filters also need to be mounted facing the right direction |  |
A shutoff valve in the fuel line is a good idea for safety, and to prevent theft |  |
Remove and measure your old fuel line carefully |  |
Use a tubing cutter to cut tubing cleanly and squarely |  |
File away the burrs on the edges of the cuts |  |
Round off and deburr the inside lip of the flare |  |
Use the gauge to determine how much tubing should stick out of the tool |  |
Tighten the flaring tool evenly to insure a clean, straight flare |  |
Flare should match up nicely and seal using the flare nut to finish the crimping |  |
Insulation on fuel line keeps petrol cool and prevents vapour-lock |  |
Set your ¨leaking petrol ¨tank on ¨sawhorses and ¨fill it with water ¨to check for leaks. ¨Use a grease pencil to mark leaks. |  |
Words & Photos: Jim Richardson
