Mercruiser 165 over heating problem

[buck68]

I have a 1981 Bayliner Santiago with a 165 Mercruiser in line 6 cylinder motor. I have a major overheating problem and I suspect it is because it is not plumbed correctly. I'm not real savvy on boats but here's what I can tell. The water from the outdrive pump goes to a 4" heat exchanger and then back to the riser at the back of the exhaust manifold. From what I can gather this is correct. I have pulled to hose off going into the outdrive and started the motor with the rabbit ears hooked up and water comes out the hose, not a lot at idle but more as you throttle up. I then pulled the hose off going into the riser at the rear of the exhaust and get the same thing so I assume the outdrive pump is working and there is not blockage from there to the riser. On the closed system I have a recovery tank with radiator cap on it that I fill with antifreeze that is plumbed into the heat exchanger and then goes into and out of the engine water pump and back to the heat exchanger. There are heater hoses that go to and from the cuddy cabin to the front of the engine. There are NO hoses going into and out of the exhaust manifold and I suspect this is my problem. I hired a mechanic (car) to tune up motor while I was at work and when I got home he mumbled something about heater hoses going to exhaust and removed them. Can anyone tell me the right way to plumb this so I can enjoy a little water time before winter? Any help would be greatly appreciated.