Mercury Fuel Pump Diaphragm 31503A1
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Mercury MerCruiser Quicksilver 31503A1 is a genuine Mercury Marine fuel pump diaphragm used in select older Mercury outboard fuel pump assemblies. Mercury parts references identify the earlier 31503 as DIAPHRAGM, FUEL PUMP TO GASKET, with 31503A1 shown as the current functional replacement. This diaphragm is used inside the fuel pump assembly to help maintain proper fuel-pump operation on supported applications.
Key Features
- Genuine Mercury Marine / Quicksilver diaphragm reference
- Fuel pump diaphragm / fuel pump-to-gasket sealing component
- Used in supported older Mercury outboard fuel pump assemblies
- Current Mercury reference: 31503A1
- Earlier reference: 31503
- GTIN / UPC reference: 745061075283
- Catalog package reference: approximately 4.50 in. x 4.50 in. x 0.20 in.
- Catalog weight reference: approximately 0.01 lb
Engine Compatibility
This diaphragm is shown in Mercury parts references for select older Mercury outboard fuel pump assemblies, including Mercury 60, Mercury Merc 110 / 9.8, and 39 / 40 HP 1-cylinder applications depending on serial number range and fuel pump assembly. Supporting application data also associates 31503A1 with Mercury 3.9 / 1-cylinder and Mercury 60 fuel pump assembly references by serial range.
Serial Number Fitment Notice
Fuel pump diaphragm fitment depends on the exact outboard model, fuel pump assembly, and serial number range. Always confirm compatibility using the Mercury serial number and parts diagram before ordering, especially where older references such as 31503 or 30652 have been replaced by 31503A1.
When This Part Needs Replacement
Replace this diaphragm if the fuel pump is leaking, the diaphragm is stiff, torn, swollen, cracked, fuel-soaked, or no longer allowing the pump to operate correctly. Fuel delivery issues such as hard starting, poor running, hesitation, or loss of power should be diagnosed before replacement to confirm the fuel pump is the problem.
Installation Notes
Service the fuel pump on a clean bench and note the order of the diaphragm, gasket, spring, and related parts during disassembly. Inspect the fuel pump body for warping, corrosion, debris, or check-valve issues before reassembly. Use the Mercury service manual procedure for the exact engine and confirm the diaphragm is seated correctly before tightening the pump hardware.
Alternate/Superseded Part Numbers
- 31503A1
- 31503A-1
- 31503
- 30652
- Mercury Marine 31503A1
- Quicksilver 31503A1
Parts Desk Insight
This is an older Mercury fuel pump service part, so serial number matching matters. The part may be listed simply as a diaphragm, but the safe match is the exact fuel pump assembly diagram, especially on older Mercury outboards where similar fuel pump parts can look alike.
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Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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