2006 hpdi 300 water pressure problem

[charliedirks]

i have a 2006 hpdi 300.i have been having water pressure problems.i have plenty of water pressure up to 3700 rpm's.at 3800-4000 rpms my water pressure bottoms out.shortly thereafter my temp alarm sounds.when i shift to neutral --my water pressure returns and remains at 20-25 psi regardless of my rpms.i replaced the water pump and impeller in hope of solving the problem.they are brand new--so it appears the problem is elsewhere.i have a 24 ft skeeter bay.any thoughts?

[boats.net]

Check to see if pressure control valve is stuck open, number 35 in this diagram Yamaha Outboard Parts 2006 and Later 2-stroke VZ300TLR 6C9-1000648 CYLINDER CRANKCASE 3 Diagram
Check thermostats are working properly.

[law1982]

2005 HPDI exact problem

I had this exact same problem on a 200hp 2005 HPDI at the exact same rpm. It took 2 months in the shop, 3 powerheads, a CERTIFIED tech, and 2 YAMAHA reps to solve the problem. The second Yamaha rep found the problem in 20mins. It was a $20 gasket in the midsection that was the problem.. Hopfully that is it.