Volvo penta engine problem

[Captain Mike]

2016 25 classic with 150hp volvo penta
Engine power problem. Engine is running fine and works perfect for about 15 - 45 minutes, then for some reason, the engine power drops off and continues to run well but only with 2000rpm as max speed.
I thought it was a fuel issue so changed all of the filters. then opened up the fuel tank to confirm the fuel is clean and that the fuel tank siphon filter was clean.
No error codes come up.
My mechanic is not a volvo dealer so he does not have access to the computer codes. He is reaching out to others to see what they think.
This is my attempt to find out if anyone else has experianced this problem and what might be causing it.
thank you

 

[S. Todd]

If your boat is a 2016 it must be a R25SC rather than the original R25 Classic. I have not experienced that problem, but the first thing I would consider given those symptoms is a temperature issue that is causing the engine to limit its speed. Does your temperature gauge indicate an abnormally high temperature? If so, does the water pump impeller need replacement or is there some other clogging problem in the cooling system?

 

[Captain Mike]

thank you for your comments
We condsidered the temperature but it seems to be normal and there is good water flow through the cooling system, so have concluded that that is not the issue.

 

[BB marine]

Check boost pressure. Could be loosing boost pressure . The turbo has adjustable vanes that can stick. If you see boost pressure decrease could be issues with ecm, vacuum pump, vacuum hose, or vanes. If turbo related. Fuel and air make power in a diesel. The common rail have a lot of electronics that control that. This is one of many things that can cause power loss but easily checked ( boost pressure)

 

[Captain Mike]

thank you, will share this with my mechanic?