SERVICE :: Service Tip #3

Many Perkins or Perkins Sabre marine engines have heat exchanger housing made of aluminium. Aluminium offers great weight savings over the old bronze housings. The down side of aluminium is that is very low on the galvanic scale and so is very prone to electrolysis or galvanic corrosion damage.

The typical heat exchanger consists of an aluminium housing, a cupro nickel heat exchanger "tube stack" and bronze end caps. The end caps are sealed using a rubber o-ring. As long as the o-ring doesn't leak, everything works great. Once the o-rings leak though, the sea water bonds the bronze, copper and the aluminium, effectively creating a battery (dissimilar metals in an electrolyte). The less "noble" aluminium will give up electrons to the copper and bronze causing pitting. Eventually the heat exchanger will start leaking very badly. When the end caps are removed for inspection, the damage is revealed. This damage can seldom be repaired. It usually requires the replacement of the aluminium heat exchanger housing.

What can you do, you say? Change the o-rings every year. The o-rings are generally less than $10. The aluminium housing will set you back anywhere from $700 to $7000! It is well worth the time and money to change those o-rings annually.

In recent years, the Perkins Sabre marinization has started using plastic end caps which eliminates this problem. If you have any questions as to what you have, or just want to prevent leaks, change those o-rings every year when you do your annual maintenance: flush your cooling system and "tune up" your engine.

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