350 alpha overheat

[blownmirage]

just hoping to get a little help, I have a 1990 350 mag engine with a gen 1 outdrive, the only problem that I have is overheat when I idle for a while, not when above 1200 rpm, I can put it in nuetral and cool engine, engine is fresh, new thermostat, manifolds are new, new circ pump, and new pump in outdrive, was wondering if switch to a engine mount sea water pump might cure this and has anyone converted this way, what do I need to do, or do you think I have another problem, any help is greatly appreciated, it had the same problem before all this I installed the blower and rebuilt the motor
thanks,
Larry
Blown Mirage

[Havasu Hangin']

How much water is flowing out at idle?

[blownmirage]

can't really tell, has some on the trailer with hose hooked to it but that has some pressure also, I would suspect needs more?, but not sure, puzzles me as I can run all day wide open and runs cool, only at idle, takes about 5 minutes to get to hot, base idle is about 700

[Havasu Hangin']

Did you try the trash can trick (instead of the hose)?
Low flow may mean you have a blockage (old impeller veins, etc.).
Where is the sensor mounted?

[blownmirage]

have not tried trash can, but have had same problem with previous outdrive water pump, installed new with whole housing assembly and new gaskets, impeller, everything, sensor is mounted in thermostat housing and when gauge gets to hot, then sound alarm start to buzz, they are 2 seperate sensor in the thermo housing, so I know it is really getting hot, have blown through hose to engine with outdrive off to make sure no restrictions and all ok, circulation pump and all parts used are mercruiser, no aftermarket except engine hard parts,

[Dr. Eagle]

Like HH says, I'm betting on an obstruction in your cooling system. Probably impeller vains, but could be anything that got sucked up into the engine....

[Chadzilla4ever]

Your problem could be one of 2 things. 1 There is a plastic housing that is attached to the upper gearcase next to where the vertical shaft goes inside the upper. This is called the water pocket. It holds the water tube in place that fits into the water pump. If that water pump has ever failed and the engine has overheated the water pocket usually gets melted because the exhaust hits it directly. If you pull the drive off you can see the water pocket. Look where the shaft goes into the upper and you should see a plastic housing with a copper tube going into it . This is it. It shouldn't look burnt at all. If it does it needs to be replaced. 2 There is a seal that is supposed to go around the vertical shaft on top of the pump itself. If the seal isn't there it will cause low water flow at idle. WELL, I hope this helps you out

[blownmirage]

don't know about that for sure, but will pull drive off soon and check since only takes a few minutes, takes longer to get boat out of garage, thanks