Melling Engine Multiple Displacement Pressure Relief Valve

Melling and the Multiple Displacement Pressure Relief Valve

Engines with cylinder deactivation, such as GM's Multiple Displacement System (MDS) and Active Fuel Management, rely on engine oil pressure to work. An oil pump feeds a solenoid-controlled valve assembly, and that assembly adds or removes pressure at special lifters to switch cylinders off and on. The pump's pressure relief valve has to hold system pressure steady through those transitions. That is why this small component deserves attention when you are rebuilding or repairing an engine that uses cylinder deactivation.

Melling has built oil pumps in Jackson, Michigan since 1946, when George Melling Sr. and his son Ben began producing aftermarket pumps. The family-owned company introduced its first high-volume oil pump in 1952, and oil circulation has remained its core discipline for generations. The relief valve is the part of a pump that sets maximum pressure, so a company with that background brings useful experience to it.

The Melling MOPR100

Melling's offering in this category is the MOPR100 oil pressure relief valve. It is listed for GM LS-series engines and is a five-port design with a male-threaded terminal. It is 1.621 inches long and sold individually. It is built for standard replacement applications rather than as a performance conversion, so it suits owners who want to restore factory-style pressure regulation. Melling describes its relief valves as built to stringent specifications from quality materials.

One detail is worth checking before you buy. Relief valve hardware and pump springs are often treated as separate parts, and the spring rate determines the final pressure setting. Melling's technical director has described the industry rule of thumb for relief settings as about 10 psi for every 1,000 rpm of engine speed. That puts a 6,000 rpm engine at roughly 60 psi. Retailers list the MOPR100 with a 60 psi maximum rating, which fits that guideline for typical street engines.

What to Consider When Choosing a Relief Valve

• Application match: Confirm the engine family and whether it uses cylinder deactivation, since these systems depend on stable oil pressure.
• Port configuration and length: The five-port design and 1.621-inch length should match the original valve.
• Pressure rating: Match the relief setting to the engine's intended rpm range and the pump it is paired with.
• Pump condition: A worn pump, damaged bore, or contaminated oil can undermine a new valve, so inspect the whole oiling system during a rebuild.

Why Melling in This Category

Melling designs and manufactures its pumps in the United States. The company also supplies a broad range of pumps, repair kits, and pickup screens, so the relief valve fits into a wider oiling-system catalog that includes the LS pumps used in cylinder-deactivation engines. For more on the company, visit the Melling brand page. To compare other options, browse the full Engine Multiple Displacement Pressure Relief Valve category.