Perkins M90 Heat Exchanger Drain Rework
A small amount of antifreeze was showing up under the aft end of the heat exchanger on the bilge pad under the engine and I went hunting for the source. I was able to localize it to the aft end of the heat exchanger and I thought that it was the plug in the end cap of the heat exchanger (never mind that this plug happens to go into the salt water side of the heat exchanger and could not have been the source of the leak). I tried tightening up on this drain plug with a stubby wrench and only put a small amount of pressure on it before it snapped off as seen below. This is the aft end plate of the cooling water heat exchanger on the Perkins M90. The end plate has an o-ring gasket to keep the salt water in. It turned out that the leak was the o-ring gasket due to the three nuts not being quite snug enough. However, it is clear that there is a case of "de-zinc"afacation where the bronze or brass (I am assuming it was bronze but someone might have lost it over the years and installed a brass replacement). So, off to the shop to have the threads cleaned out. Another good look at the corrosion process. I took the part off to S&W diesel where they mounted the part in a milling machine, drilled it and re-tapped the threads with the tap running down the original threads perfectly. Those guys do amazing things! I then replaced the plug with a pencil zinc and bronze plug. It is not clear if there was one in there before but it appears it would be a good idea due to this issue.