overheats at high rpm

[nautico 19]

Have a pair of 1999 50 D tohatsu on a Nautico power cat, both over heat at high rpm cleaned carbs they didn't look bad,no change, changed water inpeller, no help, changed thermostat, no help cleaned carbs again no help. checked fuel lines,ok checked check valve type that threads into tank ok has two 38 gal in hull tanks. Line is 1/2 inch out of tank for four feet changes to 3/8 3 more feet of hose into fuel water filter seperator 3 foot of 5/16 to motors. Too much hose? wrong size? Bad fuel pump????

 

[TOHATSU GURU]

Re: overheats at high rpm

The engines are mounted to high on the transom or both waterpumps are worn.

 

[andy6374]

Re: overheats at high rpm

What's telling you they are overheating, warning horn? Temp gauge? Are the too hot to touch for even a few seconds?<br /><br />If you had a water pressure gauge this would be easier to diagnose.<br /><br />Does anyone know if these motors have a head gasket?

 

[TOHATSU GURU]

Re: overheats at high rpm

They have headgaskets.

 

[andy6374]

Re: overheats at high rpm

Well, then one more option if everything else checks out is that your head gasket is blown or slightly leaking. This would cause exhaust gases to enter your cooling system and the end result is an overheating situation.<br /><br />good luck

 

[nautico 19]

Re: overheats at high rpm

both water pumps were rebuilt with complete kit. water trail good at idle. Boat was purchased used this year with less than 25 hrs on motors, boat was winterized and stored for 3 years thats why I cleaned carbs rebuilt water pumps and changed thermostadts. motors run fine up to 4,000rpms. What is the correct mounting height for these motors. How far below the hull should the cavation plate be?

 

[andy6374]

Re: overheats at high rpm

For a single engine setup (mounted @ the center of transom), the anti-cavitation plate should be nearly at the same level or an inch higher than the very bottom of the boat.