Fuel pump failure when the car is hot can be traced to several key factors related to temperature and mechanical stress. While fuel pumps operate, they generate heat. If excessive temperatures are experienced by internal components such as the motor or the fuel pump relay, it can lead to internal failures of the pump. The heat can cause the materials inside the pump to expand, resulting in a failure mode. For instance, a common fuel pump motor is designed to work very efficiently between 32° and 140°F. Temperatures above these thresholds – usually above 160° – increase the chances of failure significantly.
A lot of the time, fuel pumps will start to overheat, as fuel generally cools it down and they become very inefficient in cars as time goes by with lower-than-full fuel tanks. Without enough fuel inside the fuel tank, it is tugged upwards with force by the pump, resulting in its overheating. In fact, one of the primary reasons most motorists experience fuel pump failure when driving with low fuel in their tanks and having covered quite some distance. For instance, several reports indicate that close to 20% of fuel pump failures are related to low fuel levels, especially in higher mileage vehicles.
Older or malfunctioning fuel pumps often utilize brushes that may wear out over a period of time. Under hot conditions, these worn-out brushes can cause an electrical short, resulting in either a partial or full failure of the fuel pump. A study by the National Institute for Automotive Service Excellence revealed that nearly 30% of fuel pump failures occur because of electrical malfunctions, often exacerbated by high heat.
Additionally, some models are more inclined to fuel pump failure due to heat. For example, there have been several models from both Toyota and Honda that are prone to fuel pump malfunction once the car has reached an extremely hot temperature, specifically in states with ambient temperatures over 90° constantly. This is because, inside the fuel tank, the fuel pump becomes less effective at transferring fuel under increased temperatures. If not kept cool, it may either become clogged with debris or gummed up by the fuel itself, causing the entire system to fail utterly.
In extreme cases, heat-related fuel pump failures result in stalling and inability of the engine to start, especially after driving for some time. For example, some Ford F-150 owners reported that their fuel pumps were always good while their engines were cold but stopped supplying fuel to the engine once it reached operational temperature. This was sometimes attributed to a defective fuel pump relay or overheating within the pump.
However, in general, high temperatures are the major reason for Fuel Pump failure, especially in older vehicles or higher mileage ones. A recent study by the Automobile Association had noted that the fuel pump failures were responsible for about 15% of all the engine-related breakdowns with temperature-induced malfunction being one of the leading causes. To avoid these failures, periodic maintenance of the fuel system, such as not running the fuel tank too low and periodically inspecting the fuel pump, will help in longevity and proper functioning.