Every time you drive your car, the oil filter is the first line of defense against microscopic debris that could damage your engine. But have you ever wondered what goes inside an oil filter and how it works? An oil filter is made of several key components, and their materials and construction are what make the difference.
What is the Role of the Oil Filter
The primary role of the oil filter is to clean the engine oil as it circulates through the engine’s components. This process is essential because clean oil ensures smooth and efficient operation, reduces wear and tear, and prevents the accumulation of harmful deposits. An effective oil filter captures a variety of contaminants such as dust, metal shavings, and combustion byproducts before they reach the engine.
The quality of an oil filter is often gauged by three metrics:
Efficiency: This measures the filter’s ability to block contaminants of specific particle sizes, indicated by the size. A lower micron rating signifies a higher precision in filtering smaller particles, which are often the most harmful to engine components. The standard measurement in testing is efficiency at 20 micron.
Capacity: This is the volume of contaminants the filter can hold before becoming saturated. A higher capacity allows the oil filter to capture more impurities over longer intervals, ensuring engine protection for more miles of driving.
Restriction: Also known as flow rate, this parameter measures the ease with which oil passes through the filter. A good flow rate is crucial because it ensures optimal engine lubrication without restricting oil circulation.
Anatomy of Spin-On Oil Filters
A spin-on oil filter is a filtering tool that is comprised of many components working in tandem to protect engines from harmful contaminants within the oil. Each component has a specific function in the filtering process.
Steel Shell
This is the metal container that encases the filter media. It needs to be strong enough to withstand the pressure and temperature fluctuations of the engine environment. This shell shields the filter media and plays a crucial role in managing oil flow.
Attached to the open end of this shell is the threaded baseplate, keeping all the components securely inside the filter. The baseplate is engineered with inlet and outlet ports that direct the flow of oil into the filter media and back out to the engine.
For spin-on filters this steel shell becomes an all-in-one unit that houses all the filter components. In cartridge filters, the design is slightly different. There's a permanent housing bolted directly onto the engine block that acts as the shell. With cartridge oil filters, this housing doesn't get replaced during servicing. Instead, only the inner cartridge, which contains the filter media, is replaced with a new one.
Relief Valve
The relief or bypass valve is designed to prevent oil starvation in the engine. If the filter media becomes clogged or the oil becomes too cold and thick, the bypass valve opens, allowing unfiltered oil to circulate through the engine instead of being blocked entirely. It's better to get unfiltered oil to the engine than no oil at all.
Filter Element Assembly (Media, Cores, End Caps)
The key component group in a spin-on oil filter is the filter element assembly constructed of filter media, a core (steel or nylon), and end caps.
The media is the heart of the filter where actual filtration occurs. It is made from one of the following materials, which affects the filter efficiency and capacity:
Traditional Cellulose: Strikes a balance between efficiency and capacity, suitable for standard vehicle requirements with conventional oil change intervals.
Synthetic Blend: Enhances filtration efficiency without affecting the filter's capacity.
Full Synthetic: Offers high efficiency and capacity, ideal for heavy-duty applications, commercial vehicles, high-performance engines, and extended oil change intervals.
The design of the media often involves pleats, which increase the surface area for filtration within a compact space. However, it's important to remember that the quality and material of the filter media are more critical than the number of pleats it contains.
The steel and nylon core acts as the central pillar, providing strength and stability to pleated filter media and preventing it from collapsing under pressure. The end caps, on the other hand, provide structural support to the filter media and create a chamber for the oil to flow through. These end caps can be made from a variety of materials.
Anti-drainback Valve
Modern engines rely on a quick oil supply upon startup. The anti-drainback valve plays a key role in this by preventing the oil from draining out of the filter when the engine is turned off. This ensures a sufficient amount of oil is readily available for lubrication when the engine is restarted, minimizing friction and wear.
The anti-drainback valve comes in various materials. Nitrile valves are common in standard filters, but they can become brittle and crack when exposed to excessive heat. Filters with silicone valves, like FRAM Synthetic Endurance™, exhibit better resistance to heat-related issues and deliver maximum engine protection.
Gaskets and Seals
The primary function of a gasket is to create a tight seal between the filter and the engine block. This prevents engine oil from leaking out, which could starve the engine of lubrication and cause damage. While gaskets are designed to last for the life of the oil filter, they can wear out over time or get damaged during installation. It's crucial to inspect them whenever you replace the oil filter. If they appear cracked or worn, they should be replaced to prevent oil leaks.
Anatomy of Cartridge Oil Filters
Cartridge oil filters include only the filter media element and applicable gaskets or O-rings, without a housing. This design has been adopted by several vehicle manufacturers to reduce overall weight and increase the vehicle's reusable content.
Permanent canister: Bolted onto the engine block.
Replaceable filter element: Similar to the filter media in spin-on oil filters, this traps contaminants. Only the replaceable filter element inside the canister needs to be changed, while the canister itself remains on the engine.
Bypass valve: Located within the canister housing, it functions similarly to the relief valve in spin-on filters, keeping the oil flowing when the filter is clogged.
How Oil Filters Work
When the engine runs, oil circulates and enters the filter through the inlet ports and is directed into and through the filter media. The media traps contaminants like dirt, metal shavings, and combustion byproducts as the oil flows through. Clean oil exits the filter through the central outlet and is recirculated back into the engine.
During conditions where the oil filter is clogged or the oil is too thick to pass through the media, the pressure relief valve activates. This bypass allows unfiltered oil to continue flowing to the engine. The anti-drain back valve ensures that oil does not flow back and empty from critical engine areas when the engine is off.
Will a smaller filter flow less oil?
No. Oil flow is controlled by engine operating conditions, not filter size. Advancements in filter and media design have allowed for smaller filters to meet or exceed the performance of a larger filter.
Will a small filter hold enough contaminants?
The capacity of a small oil filter to hold contaminants depends on its design and the materials used in the filter media. Although smaller filters have less surface area and volume compared to larger ones, many are efficiently designed to maximize their contaminant-holding capacity without compromising filtration quality.
Are oil filters universal?
No. There are different types of oil filters in various sizes and shapes. Different engines require different filters. Follow the specifications in your car's owner manual to ensure that the filter is compatible with your car's engine and oil system.
Is a different filter required when the engine uses synthetic oil?
When using synthetic oil, it's recommended to use a filter specifically designed for synthetic oil. These filters are typically constructed with synthetic media that can better handle the longer service intervals and enhanced flow characteristics of synthetic oils. Our most durable oil filter, FRAM Synthetic Endurance™, is engineered to work with synthetic oils to deliver 99% filtration efficiency for 25,000 miles (40,000 kilometers).
Questions? We're here to help. Reach out the FRAM specialists for product and maintenance support.
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