As a graphic aid, see the following thread where there are diagrams of the 427 systems. My comments here are for all systems, not just the 427 system.
http://www.network54.com/Forum/424840/message/1123102009"
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In addition, anyone wanting information about their Sherwood sea water pumps, check out the following two links.
Sherwood sea water pump as used on the 283F, 327F, and 427
http://www.network54.com/Forum/424840/message/1156595176/
Old style 4-port Sherwood as furnished on the early flywheel forward 283.
http://www.network54.com/Forum/424840/message/1156386823/
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ABOVE: The CC Pressure Relief Valve, probably not touched for 20, 30, or 40 years and needing minimum attention, but subject to being held open if debris gets into the system. See threads below for lots of additional photos.
Today as I was working on my latest restoration project, I discovered something I want to pass on to everyone. I hooked up a water source to my 327F, fired up the motor, and the exhaust manifolds were overheating. I shut things off, ran the hose some more, took off some of the fittings, and I discovered water was not reaching all parts of the motor. Why?
Well here's why on the 327F, and this may well apply to many of our CC motors. The 327 is tilted with the forward part of the motor higher than the prop shaft side, like most of our motors are. Mercrewser's is tilted the opposite direction, but he's running a V-drive, but the same issue will apply.
Water runs uphill only when it's pressurized. For some reason I couldn't make water run uphill to the front of the motor, but when running a lot of water through the motor, and seeing it come out the tailpipes, I was puzzled (for a minute or two).
Since I knew the water was making its way to the tailpipes, I decided to take a look at those pressure regulators at the back of the motor, in this case they are attached to the risers. Sure enough, BOTH were stuck open, due to debris. One looked like it had a little twig holding it open, and the other had a bit of debris I couldn't identify. I took both apart, ran a screwdriver around the parts that touch, and cleaned em out. This time when I put things back, those valves kept water from immediately draining out of the back of the motor, and allowed the water under pressure from the hose and water impeller, to reach the front top side of the motor.
With those pressure regulator valves being held open, the water took the path of least resistance, and it drained immediately out the back of the motor.
If anyone has LOW SPEED OVERHEATING, a pair of stuck open pressure regulator valves could well be all of or part of the problem.
When you're under idle conditions, those valves cause almost ALL of the water to go through the motor. When engine speed increases and the pressure builds up inside the motor, they open up and allow water to be wasted right into the riser. If these guys are stuck open, you may be able to run well at speed, but when you slow down your motor may be starved of water, and looking at the tailpipes could be very misleading because you'll still have water coming out (but it will be short circuited, as your motor is cooking).
Regards, Paul