https://cimg2.ibsrv.net/gimg/www.off...4b3bb463ed.jpg

https://cimg3.ibsrv.net/gimg/www.off...2bb8d980bd.jpg

So on my engine the header kit came with short rubber hoses and stainless plugs so the original hoses, chokepoint and oil cooler get blocked off as the headers dont back drain.

in the first pic you can see the plug on on the chokepoint by the 2 hoses for the coolfuel

the other one that plugs the t inlet on the oil cooler wasnt used since i used a different oil cooler and mounted were the port side airvalve drain thing used to be


you can test if the backdrains failed open by blocking them off

Remove the hoses that go from the backdrains to the choke point and oil cooler, get a foot of hose whatever diameter is on them, 4 hose clamps and a dowel rod, cut the hose into 4 sections stuff a dowel in there and clamp them in place.

that will force the cooling water to follow the circuit around to the heat exchanger same as if the backdrains closed from pressure off the seapump.


mine and every other 496 with cmi headers has the backdrains deleted so it wont hurt the engine.

i would do it only as a test to troubleshoot it and replace if needed since this engine is stock before i paid 140 bucks an hour for soms greasy boot mechanic to walk over and scuff up the boat after it sat in their parking lot uncovered for 2 weeks because "we dont cover and uncover boats" until they get around to dingin you for 700 bucks.

The Perko Tee is the one that has the checkball in it. It's spring loaded. The checkball is not needed, and I recommend removing it. That's the exact issue a friend had with his 30' Baja with 496 Mags. They would run fine up to 45mph or so, but anything over that, they were not getting enough water, and overheated. The checkball was gummed up with seaweed and was not allowing enough water into the engine.

Hey all. This is the fitting that is at the bottom on each manifold. It has no spring or anything inside it, just a check ball.
https://cimg4.ibsrv.net/gimg/www.off...ac9e53c7c.jpeg

Yes that is the part I was referring to originally and you are correct just a ball. What Sydwayz was most recently talking about is a Perko product unrelated to this which allows you to flush the motor without muffs on the outdrive. Its a valve that tees into the incoming raw water supply from the outdrive. It has a one way check valve with a spring.

Jadento

So the perko valve is before the sea water pump which is where the mechanical fuel pressure gauge reads from. I cant see it pegging the gauge past 35 if it was blocking water.

Do mechanical water pressure gauges go bad?

John

We/He has never used the mercury pump out system, so I believe we could eliminate the check valve with no problems. we have a couple things to try still. but may end up trying the delete. Thanks for the info.

John

This thread covers how the system works......

https://www.offshoreonly.com/forums/...ve-496-ho.html

Where should I install a pressure bypass. It already has the fitting to dump it out the side of the boat. on the input side to the water pump or the output?

Did changing these Drain "T" fittings correct the overheating problem? Were they plugged up or bad? I'm having a similar overheating issue and all raw water pumps, impellers, gaskets, and t-stat have been changed.