Originally Posted by
brianb
All boats will have a device to mix the raw water coolant with the exhaust stream and them pump it out the back. According to my local tractor mechanic this is the most common failure he sees in all diesel installations. The exhaust stream slowly closes down and the engine cylinders then don't empty fully after combustion, causing a noisy popping sound. A way to test this is to remove the this heat riser and run the engine for a minute with no exhaust (muffler). It will fill your cabin with exhaust, but only for a minute. If the engine runs well then that is the problem. When, and if, you do this the noise in the boat will be very loud. Kind of like the GTO all the hot guys in high school tooled around in.