mercruiser overheating

[wkb2460]

My friend has a 2000 Mercrusier 350 Magnum with an alpha gen 2 outdrive.
The boat sat for a year and when we started it this season it was running a little hot. We replaced the waterpump in the outdrive and the thermostat but it is still running a little hot.
When we checked the exhaust risers one was warm the other cold. I don't have the tools to give exact temeratures on the risers.
My friend is concerned as his previous engine acted the same way before it died. It is in a 1987 Wellcraft.
My friend pulled the risers and they seem clear, also the waterpump impeller was intact when we replaced it, ie no parts obstructing the cooling system.
Any help would be appreciated.

 

[nickcasa]

Re: mercruiser overheating

ill try and offer some advice here since everyone has been so good to me....

if you run in salt water, sounds like the manifolds / risers are coroded and restricting your water flow, you really should use an IR temp gun to check them both

is there more water coming out of the tell tale on one side or the other? if so, definite blockage, replace the manifolds and risers before they rot out and water goes back into your engine and locks it up...i just got manifolds and risers on ebay for my v8 gm for $440, free shipping, only takes about 1.5 hours to change them both, not hard at all.