I purchased my boat last year and noticed while I was idling for about 30 minutes or more I heard a loud whine and wrote it off as an belt squeal. However, a few episodes later the motor would sputter, stall and die if I didn't feather the throttle. The whinning turned out to be the high pressure fuel pump. I replaced the entire fuel pump assembly and the same problem occurred but the whine was not as loud and the motor did not stall. I also noticed that when the pump was whinning it was very hot.
The HP pump is cooled by the fuel it draws from the vapor reservoir which, has a raw water cooling jacket around it. The water enters from a 1/4" diameter hose to a connection at the bottom of the reservoir and exits out the top to a connection on the Port side exhaust riser. Because the new pump was hot and whinning I decided to check the cooling hoses to be sure they were not kinked or obstructed. I disconnected the hose at the exhaust riser and had my helper start the engine. What happened was cooling water from the exhaust riser shot out of the connection and water from the end of the hose flowed freely from the Vor reservoir cooling jacket.
The water flowing from the hose told me that water was circulating thru the vapor reservoir cooling jacket. Because water was also coming out of the riser hose connection maybe this was creating some resistance when the hose was hooked up to it. So, I plugged the riser connection and let the end of the cooling hose lay towards the bilge and started up the motor. I let it idle for over an hour and the Vapor reservoir remained cool to the touch and the pump was barely warm and never whinned.
My summary is at idle when the raw water pump pressure is low the Vapor reservoir cooling system cannot overcome the the exhaust cooling water pressure and restricts or severely impedes the free flow of water circulation. However, when the engine rpms are up and the raw water pump pressure is increased the system works fine. It's when the engine is idling for extended periods of time and the raw water pump pressure is low seems to be the problem.
Because I do a lot of idling over extended periods of time I am considering plugging off the riser connection and allowing the VR cooling hose to dump overboard through a thru-hull fitting in the transom.
The HP pump is cooled by the fuel it draws from the vapor reservoir which, has a raw water cooling jacket around it. The water enters from a 1/4" diameter hose to a connection at the bottom of the reservoir and exits out the top to a connection on the Port side exhaust riser. Because the new pump was hot and whinning I decided to check the cooling hoses to be sure they were not kinked or obstructed. I disconnected the hose at the exhaust riser and had my helper start the engine. What happened was cooling water from the exhaust riser shot out of the connection and water from the end of the hose flowed freely from the Vor reservoir cooling jacket.
The water flowing from the hose told me that water was circulating thru the vapor reservoir cooling jacket. Because water was also coming out of the riser hose connection maybe this was creating some resistance when the hose was hooked up to it. So, I plugged the riser connection and let the end of the cooling hose lay towards the bilge and started up the motor. I let it idle for over an hour and the Vapor reservoir remained cool to the touch and the pump was barely warm and never whinned.
My summary is at idle when the raw water pump pressure is low the Vapor reservoir cooling system cannot overcome the the exhaust cooling water pressure and restricts or severely impedes the free flow of water circulation. However, when the engine rpms are up and the raw water pump pressure is increased the system works fine. It's when the engine is idling for extended periods of time and the raw water pump pressure is low seems to be the problem.
Because I do a lot of idling over extended periods of time I am considering plugging off the riser connection and allowing the VR cooling hose to dump overboard through a thru-hull fitting in the transom.
