2002 150hp mercury overheating often

i bought a new bass boat with

i bought a new bass boat with this motor. since day 1 it has over heated. ive taken it to the dealer twice for this problem.
first time they said they couldnt make it overheat. i dont think they even looked at it.
second time they replaced the water pump and said the old one was bad and that would solve the problem. the jerks charged me for it too.
i have no more than 3hours on the motor since the water pump was replaced and its overheating again. i have 0-2psi water pressure at idle and 9-12psi water pressure at full throttle. it doesnt overheat when on plane. it overheats when off of plane and above idle. ive lost confidence in my dealers' service guys and dont know where to turn. this motor has maybe 30hours total on it.

my question: is there a website with a cutaway of the motor so i can see what to attack? if this is common is there a fix i can perform? should i let it burn up and get a new motor under warrantee?
thanks in advance.

" Check the by-pass valve on t

" Check the by-pass valve on the lower right side of the block. It may be stuck open or even have been removed. This by-pass allows more water to move through the powerhead when going at high speeds when the water volume is high. At slow speeds, it closes and keeps more water running through the powerhead.
Hope this helps.
Good luck and have fun on the Water. "

great! will do tonight!
from

great! will do tonight!
from what you said i assume the pee stream is the path for water when this bypass is closed? im trying to understand where to look for it.

" I have a 1999 - 200 EFI that

" I have a 1999 - 200 EFI that experienced an overheating problem on the lake today, the water pressure would come and go along with overflow stream. What do I need to look for and can someone give me step by step instructions to check the water pump or impellers or point me to a web site where I can get an exploded assembly view to assist me. "

Go to Mercury Marine website

Go to Mercury Marine website & go to Parts Express Tab on left side. You can plug in your serial # and get an exploded view of what ever part of the unit you want.