- Jun 4, 2004
I wrote a week or so ago asking what was the normal engine operating temperature for the Yanmar 3GM30F engine. I had a new temperature gauge and was getting readings up to 180 degrees F at RPM’s above 3,000. Fred Ficarra wrote that my engine was running too hot and suggested that I should clean the heat exchanger among other things. Last weekend, we had the boat out on the bay and I began to get engine temps above 180 whenever I ran over 2,000 RPM. Something was wrong but we had plenty of hot water for the dishes that night. Keeping with the rule to check and fix simple things first, I stared at the beginning of the cooling system before tearing apart my heat exchanger and exhaust elbow. My thru hull was clear and the sea strainer was empty. There was good water flow from the thru hull and no evidence of an air leak. Even though I had installed a new impeller at the beginning of the season (April), I removed the raw water pump from the engine and took off the back cover. The impeller was in pieces. Two vanes were missing and the remaining were badly cracked but still attached enough to pump a little water. I am sorry to report that the impeller was one of those new Globe brand, blue rubber, “run-dry” impellers with less than 15 hours of service on it. I replaced the impeller with a new Yanmar replacement unit and a new “O” ring. I found the two broken vanes stuck in the raw water entrance port to the heat exchanger and was able to easily remove them with a tweezers. We took a short trip this week and of course, the wind was right on our nose both ways so I had to motor to and from our destination. I motored a total of five hours directly into a 12 to 20 knot head wind, at 2,800 RPM, towing a dinghy at from 5 to 6 knots. The engine temperature stayed between 156 and 159 degrees all day. There was no steam at the exhaust. Lessons learned? The wind always blows directly from where you want to go and the normal engine temperature for the 3GM30F Yanmar (on my boat) is at or below 160 degrees F.