Why Does a Fuel Pump Fail When the Tank Is Half Full?

Even when the fuel level is half of the capacity, there are several possible causes due to which a Fuel Pump may fail, owing to factors concerning the design of the fuel system and the nature of the operation of the pump. In most modern vehicles, there is an electric Fuel Pump that is normally located inside the fuel tank and draws fuel from the tank and delivers it to the engine. When the fuel level goes to half or less, fuel pumps can develop air pockets, which means that air can get in, and then the pump struggles to draw the fuel. This can cause overheating of the pump and thus its failure.
The Automotive Fuel Systems report (2023) indicates that around 30% of fuel pump failures occur when the tank is less than a quarter full due to the inability of the pump to maintain a proper flow of fuel. This is very common in older vehicles where the fuel pumps are worn out and depend on the weight of the fuel to help push the fuel towards the pump. If the level of fuel drops, air is sucked into the system, and the pump starts overheating due to increased friction, which leads to premature wear and failure.

The failure of a Fuel Pump in half-full conditions is also often linked to contamination within the fuel tank. When the fuel level is low, dirt, debris, and water can settle at the bottom of the tank. These contaminants may be sucked into the pump as the Fuel Pump draws fuel from the tank, causing damage to the components of the pump. According to a report by Consumer Reports, 2021, 40% of the failures of the Fuel Pump are due to fuel contamination, which is always more serious when the tank is not full. The fuel pump therefore has to work harder by pulling fuel through the filter, the chances of it getting clogged and failing increase when it is at lower levels.

This issue is further contributed by Fuel Pump not being cooled sufficiently. Normally, fuel pumps are cooled down by fuel surrounding them, which helps control their operating temperature. When the level of fuel is low, there will be less fuel around the pump, and it will not cool properly. Overheating may affect the pump by causing damage. According to AAA’s 2022 study, about 35% of overheated, failed fuel pumps are mainly because of running low levels of fuel; this factor limits the cooling mechanism and might make the pump seize up more frequently.

A recent Toyota recall (2023) highlighted the impact of low fuel levels on Fuel Pump failure in certain models. The customers have reported that when the vehicles had half or lower fuel levels, they would stall and hesitate to accelerate due to overheating of the pump caused by low fuel levels. This problem led to significant engine misfire issues and costly repairs for many affected customers.

Fundamentally, it all begins with the design nature of many fuel pumps,” adds Markley, a senior propulsive systems engineer at FuelTech Solutions. “When a tank is below half full, pressure inside the fuel pump itself begins to fluctuate wildly. As a pump constantly stresses out trying to work on this fluctuation, which increases with speed, eventually, it fails over a certain period of time.

Worth noting, though fuel pump failure at half-full levels is not that common, the conditions can be right under which it does occur. A neglected Fuel Pump, or frequent short trips, or a history of low-quality fuel could increase chances of this issue occurring.

It is always advisable to replace your fuel pump if you start to have any kind of fuel system troubles, like hesitation, stalling, or difficult cold starts-when your tank is below half-full-for reliable performance and to avoid failure. High-quality replacements, such as those provided by Kemso Fuel Pump, have been made to guarantee a continuous fuel delivery with longevity and minimize the chances of failure when fuel levels are always in fluctuation.

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