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Old 07-07-2007
Irwin37mkIV Irwin37mkIV is offline
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1967 Irwin 37 cc with exhaust problem

My boat has a Perkins 4-108 engine with manifold on the port side. The exhaust leaves the manifold and crosses to starboard via an anti-syphon loop over the transmission, raw water is injected on the downstream side of the anti-syphon loop before entering the aqua-lift muffler on the starboard side of the engine compartment. Exhaust then crosses back over the transmission, forward under the hall floor, and out through the port hull at the waterline, via the cavity between the sette and port ice-box (i.e. behind the electrical panel compartment.)

Problem: Exhaust is wrapped with asbestos cloth ahead of the water injection point and is very hot. Exhaust appears to be made of copper pipe with soldered elbows and injection tee, with solder joints ready to fail. The rubber exhaust hose needs to be replaced, and am thinking of rerouting the entire system, as it does not appear to be the original installation...

There is a 2" through-hull fitting below the floor (under an inspection hatch in the Halway. This thru- hull is capped. I suspect that this was the original discharge point for the exhaust. It is about 2' below the water line. Can anyone confirm that the original exhaust discharged at this location?

Would a replacement have been routed to discharge at the waterline to avoid syphoning water into the engine? The present configuration introduces a second loop aft of the muffler where water is constantly trapped, and results in additional backpressure. The 'uncooled' anti-syphon loop is a significant obstruction, particularily when trying to do service work in the engine compartment when hot.

Has anyone done a successful retrofit on an exhaust, injecting cooling water directly after/below the manifold and placing the anti-syphon loop aft of the muffler, then discharging below the waterline at the hall floor hatch cover? I have read several publications suggesting that discharge below the water line is viable with an additional anti-syphon in the cooling water loop. These are generic documents, not specific to this boat and model. I'm concerned that the abandoned thru-hull, while accessible, is too far below the waterline to be put back in service?

Comments welcome.
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