There are four engine zincs on my engine. The manual does a lousy job of illustrating the locations and talks about 6 zincs. The manual shows 2 zincs on the oil cooler, one on the bottom and one on the forward end. The lube oil cooler on Stella Blue has only 1 zinc. It is located under the cooler. There are several owners of this engine that report very fast corrosion of this zinc. The oil cooler zinc on this boat is no exception. It must be replaced at least twice a year and there is nothing left at that time. I must monitor more frequently as a result to protect the metals in that cooler. The intercooler has 1 larger zinc at the aft end and is easy to see. Lasts all season.
The two on the heat exchanger are also easily accesible. The 6th zinc the manual speaks of, is in the transmission oil cooler on the Yanmar gearbox. Stella Blue has a ZF transmission and there is no zinc in it's oil cooler.