Questions please: My year 1972 Chris-Craft 47' Commander with the original twin Detroit Diesel 8V-53 engines have the standard placed wet exhaust outlets on each stern bottom side, however, these original Detroit Diesel 8V-53 engines also each have an additional wet exhaust outlet to the side of each engine above the waterline under the quarterfoil and my questions are: 1. What is the purpose of these additional wet exhaust outlets on each side of the original Detroit Diesel 8V-53 engines ??? 2. Are there additional thermostats within these additional wet exhaust outlets' systems on each side of the original Detroit Diesel 8V-53 engines ??? 3. Has anyone seen these additional wet exhaust outlets' systems on other years of the Chris-Craft 47' Commanders or the 55' Commanders or the 60' Commanders ??? 4. Do you also own this additional wet exhaust outlets' systems set up on your Chris-Craft 47' Commander ??? "Thank You", in advance, for your information and time. Kind Regards, Mark Patrick Hillman
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Edited: Jun 23
Detroit Diesel 8V-53 exhaust outlets ???
Detroit Diesel 8V-53 exhaust outlets ???
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These are normally raw water bypass systems to dump some of the cooling water overboard in an effort to reduce exhaust backpressure. My 1973 47 with Cummins VT8-370Ms had these raw water bypasses. I understand only some of the 47s with 8V53Ns have them, possibly 1970 and newer. The way the system worked on my 47 is that raw water exited the engine cooling system into a 2" tee with a valve on the bypass side and the other side open to the exhaust mixer. There was an instruction plaque on the starboard side of the engine room with instructions to open the bypass valve until exhaust backpressure was within engine manufacturer recommended range. For reference, the valves on my boat were fully open on both sides. The bypass discharges were 2" and the hoses going to the exhaust mixers were 2", so it could be assumed that approximately 50% of the raw cooling water was dumped overboard instead of going into the 6" exhaust system.
When I repowered the replacement engines pumped significantly less raw water so the bypasses were no longer needed. I converted them to exhaust bypasses using a 6" to 2" tee and ran separate 1/2" raw water telltale streams out the sides immediately below the original outlets.
Photos I posted are of the exhaust system and raw water bypass as it originally existed on the starboard side prior to repower.