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Little Mercs have very small, high pressure/low volume impellers, sort of like a 9.9/15 OMC but smaller and tighter. They take a bad set and have a strong tendency to bend a bade backward. In my experience, anything more than two years old starts to be suspect. So, 35 years…..? What if you did have a failure and toasted that beautiful thing? I know I wouldn’t trust a 35 year old Merc impeller; but your luck may vary….
Like Bill says, you don’t want to take a chance on hurting that beautiful new Merc time capsule. This engine is the last of the US Merc built two stroke 4hps, so don’t take any chances…
Replacing the impeller on these engines is pretty easy, no shift linkage to disconnect like most of the OMCs. If you decide to change the impeller, please use the OEM Merc impeller, aftermarket water pump parts can be troublesome sometimes….