Sadler 34 fuel tank

The fuel tank on a Sadler 34 is made from stainless steel, rectangular apart from a small chamfer taken off one corner to fit the turn of the hull. It has a capacity of around 100 litres of diesel and is located at the aft end of the port side cockpit locker, where it is bolted via five tangs to the cockpit wall. It is not fitted with an inspection hatch. Three nozzles are welded to the top: the fuel filler, the return from the engine and a vent. At the bottom is the fuel take-off to the engine and a brass drain plug.

After around 30 years of reliable use it became apparent that some maintenance was required. The first problem was that operation of the electric fuel level gauge became unreliable. The level was shown as accurately as normal down to about half full, when the needle became pressed hard over beyond the maximum level. As time went by this got worse and ultimately the level was not shown at all. A check on the wiring seemed to show that this was in order, so we suspected that the level sender inside the tank had succumbed to old age.

The second problem was a brown rust stain extending down the locker beneath the tank. This was caused by water leaking through the corroded brass drain plug threads.


This shows the tank after removal with all the holding mountings visible.


Having drained off all the fuel it was time to set about getting the tank out. The two forward bolts were easy enough, the two below not too bad but the aft one required long arms, a socket spanner on an extension and use of a mirror.

Once free the tank was a very tight fit through the cockpit locker lid but ultimately it came out. The first job was to remove the old sender unit. This had a round flange on top and a C-ring below, sandwiching the tank metal between them. The problem with this method is that undoing all the relatively short bolts will cause the C-ring to fall into the tank. I avoided this by substituting a long bolt with the same thread for one of the short bolts, holding the C-ring up for removal through the hole once the sender was removed.


Viewing the internals of the tank revealed a small amount of sludge, easily washed out with mains water pressure. I dried most of this water out by rinsing with acetone and the Greek sun finished the process. I replaced the old sender with a vertical tube type from Osculati after measuring the height needed. These units come in a variety of lengths and need to be selected for the duty. Calibrating the level after refitting showed that a few litres are present below the sender when the gauge shows empty.

The vertical Osculati sender comes with its own gasket, the bolt pitch circle and diameter were the same as those on the old unit. I replaced it using the same long bolt to ensure that the C-ring did not fall inside the tank.P9220061

Having replaced the sender unit it was time to address the rust stain beneath the tank. A slight drip from the brass drain plug had been evident for some time but I was reluctant to attempt tightening it further when my first attempt felt distinctly ‘wrong’ and I certainly did not want a locker full of diesel. It was just as well that I held off, because with the tank empty a quarter turn on the plug caused it to fall out. Over many years the small amount of water in the bottom of the tank had caused galvanic corrosion between the brass of the plug and the stainless steel of the boss with the result that the threads had almost disappeared.

I replaced the fine-threaded drain plug with a ¼ inch BSP plug after drilling and tapping the tank boss. A second valve would have been preferable to enable regular draining but there is insufficient space to fit one.

The fuel take-off projects upwards about 25 mm, meaning that it is not possible to remove any water that settles to the bottom, but also that this water is not drawn into the engine.


I inspected all the welds carefully. Although there is a little surface rust adjacent to them there was nothing that gave me any concern over leaks.

Getting the tank back and reconnected was not too difficult and no further problems have occurred.