2008 R25 with Yanmar 4JH4-HTL Overheating

[BB marine]

There should be a check valve in line for the head. There was one on our boat which uses the same strainer for wash down ,head and engine. I switched to fresh water flush so I removed the check valve and hose to the head and made the strainers extra fitting a flush port for the engine and a emergency bilge pump. I never liked having the head and engine using the same strainer. I also installed a shut off valve for the wash down to take that out of the equation for a air leak.

Air can not get past a ball valve unless it is damaged. We used ball valves on our air compressors 140 psi and experienced no leakage.

I would trust the ball valve before I would trust the check valve. Cutwater used the same check valve for the head has they used for the bilge pumps.

This is the check valve installed
http://www.thebosworthco.com/images/car ... o_s600.png

Ball valve installed for flush and emergency bilge pump. Replacing sea water head flush.

 

[knotflying]

On the 4BY2 engine all the info posted here and from Yanmar staff says the thermostat starts to open at 190 degrees and is fully open at 205 degrees. It would make sense that the thermostat range of opening would be at a temperature that is safe for continuous operation of the engine. As a manufacturer you would not put in a part that didn’t fully do its job at temperatures that would damage the engine the part was designed to protect would you?
During our low coolant event last year, everyone we spoke with said you could run the 4BY2 at 205 degrees indefinitely without worry. That said, we now are running 194 degrees at 3,000 rpm on our engine all day long.
Understand your engine is different. I am a bit surprised your normal operating temps (thermostat range of 170-195 degrees?) are that much lower that those for the 4BY2.

Less horsepower, less temperature.