Water damage (corrosion)

A particular type of damage through contamination is damage due to water in the fuel system.

Rust or chalk particles that are formed as the result of water in the fuel can clog the filter and cause the pump to run dry. Chalk and rust deposits on or in the fuel pump reduce the running clearance of the moving parts. This restricted freedom of movement results in increased power consumption and a reduced delivery rate, and may even cause the fuel pump to jam.

At first glance, the expression “water damage” may appear unlikely in the context of fuel pumps. However, fuel can be contaminated by water in a variety of ways:

Formation of condensation in the tank

The ambient air always contains a certain amount of water, even the air above the fluid level in the fuel tank. The volume of this water is referred to as “relative humidity”. Cooler air can hold less water than warm air, i.e. when the air cools, droplets of water may form from it to produce condensation. This can be a problem for cars that spend a lot of their time in the garage. When vehicles with a relatively empty tank are not driven for longer periods, the large quantity of air in the tank means that a larger volume of condensation can build up.

Note: Fill the fuel tank completely if the vehicle is going to be stationary for a longer period.

Improper use

Fuel pumps are designed to convey fuel (petrol, diesel). Cases actually exist where a fuel pump has been used as a “water pump”.

Fuel quality

Fuel may contain water even during the refuelling process.
Here are some possible causes:

Varying fuel quality in some countries
Refuelling from damp containers/ canisters
Badly designed filling stations
Biodiesel
High proportion of alcohol Alcohol absorbs water. When a certain limit is reached, this water is shed.

Leaks in the fuel system

Splash water can penetrate the fuel system in a variety of ways:

Refuelling in the rain
Leaky or missing tank-cap seal
Missing tank cap
Through ventilation orifices of pneumatic valves that are exposed to splash water, e.g. valves in the ACF (activated carbon filter) system
The fuel filler neck was not fitted following an accident or body repairs
Scuffed tank ventilation hose or incorrect subsequent rerouting of the tank ventilation hose

Note:
This is how you can determine whether fuel contains water: Pour a little fuel into a fuel-resistant glass (test tube), taking it from as low a level in the fuel system as possible. After a while, the water precipitates.

Attention:
Pay heed to fire safety requirements!

1 = Fuel
2 = Water

The outer housing of a fuel pump generally consists of aluminium. As aluminium cannot “rust”, in cases such as this repair shops should question what the cause might be.

If the sieve filter on the intake side of a fuel pump displays rust or chalk deposits, this is an indication of water in the fuel.

In this case, there was a veritable “pool” of water in the pump. The pump system was so corroded that the water could no longer escape. This fuel pump was misused as a “water pump”.

If rust or chalk deposits grow to such an extent that they form particles or grains, they can jam or irreparably damage the rotating parts of the pump system, just like aspirated foreign bodies.

When this fuel pump was opened, it was found to contain “sandy” deposits of chalk, which had destroyed the fins of the impeller.

The fact that the sieve filter is undamaged proves that these particles could not have entered the pump – they must have formed inside it.

There is a simple way to check the ease of movement of a trochoidal pump system:

When you roll the pump system over an even surface, as shown on the left, the toothed ring and gear must mesh smoothly.

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