merc 260 hp 350 getting hot
 

i am pulling my hair on this one,i just finished putting a transom assembly&engine [alpha gen 1]in a boat,it was removed to have the rotted transom replaced,the owner told me that it would go to 250 on the water temp gage and sound the warning buzzer before i removed everything so i replaced the water pump impeller and the thermostat.i took the boat out for a test ride and all was well until i idled for a while,then it got hot but if put in neutral and revved to 2000 rpm the temp goes down.the belt on the circulating pump is tight and not slipping.anybody have any ideas on what is causing it to get hot?

Mike a lot of times with the gen 1 alpha you have to change the whole complete water pump kit including the base under the wear plate and bottom gasket especially if it was overheated at anytime.

The new complete kit comes with housing, impeller ,plastic water tube, wear plate, 2 wear plate base gaskets and the bottom base, make sure U use the correct gaskets as the kit will come with extra different gaskets..

Also you need to use the round seal that sits on top of the water pump housing itself. Also do not torque down the plastic water pump housing one screw or one nut at a time. Do the normal 3 pass. You can warp that plastic water pump housing.

next take a look up under the upper outdrive u will see the water tube pocket and the water pocket cover and gasket itself, if this portion was overheated or leaks it needs to be changed out with new. it can cause an overheat.

Does this app have the check balls in the t - stat housing ?

Also what about the water circ pump on the front of the motor ?

Next the water inlet hose from the power steering cooler all way back to the inner transom inlet connection, is it kinked and or restrictions . How about the condition of the connector itself .

External water hose port side in the outer transom assembly a restriction, dry rotted, hole, or kinked ?

Just throwing out the common places here

if they used the cheap ebay bellows kit, the hose in the gimble kinks easily

thanks,il get the impeller kit and replace it all,if still getting hot il check these other things.

it did it with the old and the refreshed transom assembly but i will check it out.

My little boat with the 260hp motor did the same thing. When I bought the boat, I rebuilt the motor with everything NEW and it drove fine as long as you had RPM's, but soon as I come back down, to lower RPM, the b***** would get super HOT. I was pulling my hair out, hell everything was new. WTF. Well it was the little plastic balls in the T fitting on top of the thermostat housing, they were missing all together, so higher RPM the motor would have enough flow at an idle all the water was going out the manifolds and hardly any to the engine. Problem solved for about $9.00