Mercury – Water Pump Base Assembly | Cooling System | 46-42579A3

Overview

If you’ve spent any time working on the mid-range Mercury or Mariner 2-strokes—especially the 105–220HP EFI, DFI, or 2.5L jet motors—you already know the water pump doesn’t forgive a worn base. Once that base plate gets chewed up or warped, the impeller can’t build good pressure, and you start seeing weak water flow or temps creeping higher than you’re comfortable with. This OEM base assembly is the proper replacement and gives the pump a clean surface to work against again. It’s one of those parts that looks simple, but if it’s not right, nothing else in the cooling system behaves.

Key Features

 • Built for 105–220HP 2-Stroke EFI/DFI/Jet – Correct base for select Mercury and Mariner 2.5L engines.
 • Restores Water Pump Efficiency – Helps bring back strong telltale flow and steady temps.
 • Tough Marine Construction – Handles heat, grit, vibration, and constant water pressure.
 • Easy Install – Swaps in when you’ve already dropped the lower unit for pump service.
 • OEM Tolerances – Ensures the impeller sits properly and seals the way it should.

Engine & Boat Compatibility

 • Mercury 105–220HP EFI
 • Mercury 105–220HP DFI
 • Mercury/Mariner 2.5L Jet outboards
 • Select 2-stroke cooling systems

Performance & Practical Benefits

Once you put a fresh base in, you’ll usually notice the cooling system straighten up fast. The telltale steadies, temps stay where they belong, and the motor stops flirting with overheating at idle or during long no-wake stretches. Jet motors especially chew through bases over time thanks to sand and shallow water, so replacing this piece can make the whole pump feel brand-new again. And it helps your new impeller last longer instead of grinding itself against a worn surface.

Why Buy OEM

With OEM, the fit is right and the material holds up. Aftermarket bases can warp, crack, or leak—sometimes right out of the box. Cooling issues on these engines get expensive fast, so running the correct Mercury part is just the smart play.

FAQ

Q1: What tells me the base might be worn out?
A: Weak telltale, uneven impeller wear, creeping temps, or the engine running hot at idle.

Q2: Should I replace the impeller while I’m in there?
A: Yes—once the lower unit is off, it’s the perfect time to do the impeller.

Q3: Is this a do-it-yourself job?
A: If you’re comfortable dropping the lower unit, it’s very doable.

Q4: Will replacing the base help at higher RPM?
A: Definitely—if the pump can’t seal or catch water properly, it can’t keep up at speed.

Q5: How often should I check the pump base?
A: At least once a season, or anytime you’re already in there replacing the impeller.

• Supersessions
  46-8M0077147, 46-8M0077147