For the Mercruiser 470 - What should be the level of Antifreeze in the Manifold?

Question

I have had an issue where Antifreeze is spitting out out the Radiator cap when running the engine at 3000- 4000 RPM while underway . This does not happen at the dock, only when there is a load on the engine. I noticed that part of the lip of the Fresh Water Reservoir where the radiator cap goes on is missing, thus not giving the cap something to hold it down on one side. I found a replacement part, and I'm currently in the process of replacing it.

After removing the Reservoir, I notice that the Antifreeze level in the Manifold was low, less than half full. Should the Antifreeze level be up to the top before I put the New Reservoir back on?

Also, if this does not fix the problem, aside from over hearting issues, what else could make the Antifreeze leak out of the cap while underway.

Thanks!

Answer 1

you may want to pull the riser off manifold and check gasket and condition of mating surfaces. These were known to have leaked allowing antifreeze to get into number 4 cylinder slowly and it would burn off. Eventually it destrys the cylinder. They did have a service bulletin out quite a few years ago.on this problem

Answer 2

I have the same engine: I would guess it's the radiator cap, after it's replaced try it. I hope your using environmental safe anti-freeze so as not to spoil the water?

Answer 3

might have a blown head gasket