Bad Fuel Filter Symptoms

Fuel is pumped out of the ground, transported to refineries, and then transported to gas stations where it sits in big underground holding tanks. And it then flows through the pump into your gas tank. Along the way fuel, especially diesel fuel, can pick up various particulates such as dirt and grime. These particulates can harm your engine and fueling system. In this article, we discuss fuel filter problems, clogging, replacement, and more.

Understanding Fuel Filters

A fuel filter blocks dirt, rust, grime, and other harmful particulates from entering your engine through your fuel system.

The fueling system on your car is comprised of a gas tank, fuel lines, a fuel pump, and injectors. The fuel pump passes the gasoline from the tank through the fuel lines to the injectors. Filters usually sit right in between the fuel lines and the injectors.

Fuel filters are usually cylindrical cartridges with filter paper on the inside, similar to an air filter or an oil filter. The fuel flows through the filter prior to being sent to the injectors to prevent any harmful debris from passing into the injectors or engine.

Bad Fuel Filter Symptoms

• Hard starts
• Rough idling
• Engine stalling
• Cylinder misfires
• Poor performance and lack of acceleration
• Decreased fuel pressure
• Lean air to fuel ratios

Fuel filters don’t fail immediately. They tend to slowly become clogged over time. With that being said, these symptoms will usually develop slightly and then gradually get worse over time.

When a fuel filter is clogged it restricts fuel flow to the cylinders. This is commonly called running “lean”. Running lean can starve the cylinders of fuel which causes increased friction amongst the internals which can lead to serious internal engine damage.

The most common initial symptoms are rough idling and misfires. From there it will progressively get worse and lead to hard starts, stalling, and significant performance decreases.

Causes of Filter Failure

Fuel filters go bad because they become clogged. With that being said, the biggest cause of clogged fuel filters is bad gasoline. The longer gasoline sits within holding tanks, your gas tank, etc. the more dirt and grime it picks up. Additionally, on older engines especially the fuel tank and various parts of the fuel system can corrode on the inside causing a buildup of debris in the gas tank.

The best step to preventing fuel filter problems is to always use high quality fuel. Try to go to the gas stations that are always the busiest and most popular as the fuel sitting in their tanks is likely newer and fresher. Avoid rundown gas stations where the underground tanks and pumps have likely never been cleaned and the fuel sitting in them is probably old.

The other best “prevention” method is to change you filter at the recommended intervals. It’s not uncommon to see people running fuel filters past the 100,000 mile mark since they simply aren’t aware they should be changed. No matter how much you do to try to prevent clogging a filter, it will pick up dirt and grime overtime. So even if you don’t have any noticeable symptoms replacing the fuel filter is still a smart maintenance item and will likely wake your engine up a bit if your filter is old.

Problems Caused by a Dirty Filter

Outside of the symptoms listed above, a bad fuel filter can also cause your fuel pump and fuel injectors to fail.

When a filter clogs, less fuel is sent to the injectors and into the cylinders. When this happens, the fuel pump tries to fix the issue by increasing fuel flow. This causes the fuel pump to overwork itself which can lead to complete pump failure.

Additionally, the decreased fuel flow leads to lower fuel pressure as the fuel exits the injectors. This results in the fuel injectors also becoming overworked which can cause them to fail as well. If your filter is bad for a long time it is possible for it to deteriorate to the point that debris makes it past the filter. When this happens it will make its way directly to the injectors and likely lead to the injectors failing. It can also send this debris into the cylinder chamber and cause engine damage.

Fuel Filter Replacement Costs

Fuel filters themselves are usually somewhere in the range of $20-$50. The most variable part is labor which is most dependent upon where your fuel filter is located. Some are located in easy to access parts of the engine bay while others sit underneath the vehicle or in more difficult areas of the engine bay.

Fuel filter replacement usually costs $100-$200 for parts and labor. The one caveat is for vehicles who have an integrated fuel filter. Some engines have the fuel filter integrated into the fuel pump. If this is the case, replacing the filter also requires replacing the pump which can cause the job to run closer to the $500 mark.

Diesel fuel filter replacement tends to cost $50-$150 for parts and labor. Due to the frequency of replacing the filter on diesels they tend to be located in easier to access areas and are therefore relatively easy DIY replacements.