Re: Mercury Mark 6 Water pump Woes

[billw]

Not really sure how you’d do a bucket test on a Mark 6 pump…The top cover would have to be on tight; and that’s held down by the upper drive shaft housing holding spring tension on the pump cover. Anyway, assuming the obvious is okay, sometimes Mercs get corrosion build up between the stainless water pump cup and the housing that holds it, warping the stainless cup. That causes a poor fit for the impeller and they won’t pump. The top wear plate can’t be warped, either. You could also make sure the top cover fits well, that its spring tension tabs are good and that there is at least some of the seal left in the top cover, so it won’t allow exhaust gas to be sucked into the pump. Make sure the cover’s water tube grommet is good and that the water tube is engaging the grommet and not warped. The impeller should move freely up and down on the shaft so that it can seek its own mid point in the pump housing. And make sure when you barrel test, that the tank water level is at least up to where the impeller is. Mark 6 pumps are not the best set up; so everything has to be just right. As stated in your other thread, there is no tell tale per se; only mist blowing out the four little holes with the exhaust relief. A properly cooling Mark 6 should allow you to hold your thumb on top of the block indefinitely.

Long live American manufacturing!