Hi, I just received a new GMW water pump, P/N 125-3110 that as per GMW’s catalog should fit my original 256 4.2 V8.

I am at a loss because the water pump on my engine is SMALLER !!! The impeller is only 4’ while the GMW’s impeller is 4 ¾’ and besides this the shaft is way longer so the flange cannot align the pulleys properly!

Does anyone know what is going on please?

Thanks

Aris

 

Hello, Aris, and welcome to the Mercury Forums --
Per RockAuto.com, your 256 cu.in., 4.2 Liter V-8 takes GMB # 1253110 Water Pump (gasket included) @ $67.89.
Also available from RockAuto: Airtex # AW488 Water Pump (gasket included).@ $65.79
Correct Thermostat = Stant # 13478 @ $2.32
Prices are plus tax and shipping.
For fitting problems, remove the old pump and match it to the new pump. No fit !?? Perhaps you got the wrong part.
You can't call Rockauto.com, but they respond to e-mails.




95 MERC at Flaming Gorge, Utah

 

Hi 95 Merc, thanks for the information!

I have spent money on the wrong pump, so it took me some time to figure out that especially for the '54 Mercury, the water pump was special just for that year.
FYI and for anyone looking to replace their original 1954 Mercury Water Pump even though the GMB 125-3110 is listed by the manufacturer, in eBay and other retailers to fit the '54 Mercury, BEWARE THAT IT DOES NOT!!! It comes with a 4.1/2' impeller that doesn't fit onto the timing cover; The correct Mercury water pump P/N B4A-8501-C is smaller with an impeller measuring only 4 inches!

I got a reply from GMB that they don't have a smaller one that will fit and judging from the pictures online, the AIRTEX don't have one either, however there are eBay sellers offering the smaller REBUILT OEM pumps with the correct 4' impellers or you can go for rebuilt kits that can also be found on eBay, just make sure that the impeller is only 4' wide.