1960 Merc 300s Overheating

[glamrpups]

I have a merc 300s, Just did a new water pump and fule pump. Took it out started right up ran for about five min got in and started to drive, drove for about 5 min and it stalled out. Motor was every hot. let cool off and ran fine to get back in full throttle and all. Water same to be pumping but motor not cooling off. Any Ideas

 

[Fuzzytbay]

Re: 1960 Merc 300s Overheating

Idea one........don't run a motor at WOT if you suspect its not cooling properly.
Ok now when you changed out the old impeller, was all of it there?
You might have some rubber jamed up in the cooling passages, blocking some of the flow.
Its also possible to put the impeller in backwards, so it will not pump as much water as it should.