255 scarab open ID jet boat twin 300 starb side motor keeps overheating

[charles22$]

I need help I’m stumped I’ve flushed the system through coolant tank out through ride plate and refill the antifreeze I get 4-5 hours were it won’t over heat then after that as long as I’m moving 10-15 mph it won’t over heat soon as I slow down the temperature wants to rise idk if this a impeller issue or what any direction to head would be great

 

[FSH 210 Sport]

Is the fresh water coolant level changing / dropping after 4-5 hours? What prompted you to flush this system.

I’m not familiar with these boats but If I’m not mistaken there are two coolant pumps, one for the fresh water cooling system on each engine, and one for the raw water that cools the exhaust and the heat exchanger for the fresh water cooling system on the engines. So those two coolant flows have to be functioning correctly.

If it was a thermostat the problem would happen right away.

The other thing I can think of is a bad sensor. Are there any other indicators that the motor is overheating? Sounds like a code reader would be required to determine which sensor is throwing the overheating code, it could be the engine or perhaps the exhaust?

 

[charles22$]

It’s definitely over heating because the coolant starts to running out of the over flow tube

 

[FSH 210 Sport]

It’s definitely over heating because the coolant starts to running out of the over flow tube

Then it could be a lack of flow to the heat exchanger…

Any other pertinent information you’d like to include? These details help us all to help you solve your issue.

 

[charles22$]

So I had it out yesterday when I kept the boat moving above 10 mph it would not over heat soon as I would go down to an idle it would get hot as long as I was moving a decent pace it wouldn’t over heat

 

[FSH 210 Sport]

So I had it out yesterday when I kept the boat moving above 10 mph it would not over heat soon as I would go down to an idle it would get hot as long as I was moving a decent pace it wouldn’t over heat

Again, I don’t know a lot about these boats, but that sounds to me like there’s a restriction in the cooling water that goes to the heat exchanger. So if it works anything like a Yamaha, you might be getting your cooling water for the heat exchanger otherwise known as raw water, from the jet pump, have you checked the intake screen or anything like that?

 

[charles22$]

So the heat exchanger is connected to the ride plate at the bottom of the boat there’s no sea water that goes through the heat exchanger as the the boat goes across the water it cools the ride plate which antifreeze goes through from what I understand the sea water only goes through the exhaust portion of the motor there is a impeller that is in the water pump housing that pumps the coolant throughout the engine

 

[FSH 210 Sport]

Could be a thermostat then. Get a new one and install it to see if that cures the issue. Or the pump that moves the antifreeze needs attention