2-3GM(D)(F)(20)(30) engine speeds.
Tom and others, I found reference to the maximum operating engine speed of 3,600 RPM on page 3 of the smaller Yanmar Service Manual (green first page) at the back of the way larger Yanmar Service Manual I have. I can't put my fingers on the recommended 3,000 to 3,400 operating RPM information but know for a certainty that to operate for sustained periods at less than 3,000 RPM is not recommended by Yanmar. Avoidance of carbon build up in the elbow is the main reason for the higher engine speeds. I can also state from almost personal experience that operating the engine at 3,600 RPM for more than an hour will for a certainty overheat the cooling system and send the red light and sonalert ablazing. Years ago there was a period of time where Marilyn was single handing our boat to Catalina and back 32 NM each way and would have engine cooling troubles. By the way, she still single hands over, as recently as about a month ago. Typically she'd back out of our slip on a Friday around noon in order to catch the afternoon winds that would carry her to the island. She'd then motor off the mooring at the island around 1000 or 1100 on a Sunday morning to begin the passage home. With predictability the engine overheat about an hour out and she'd have to shut down the engine and catch what wind she could in order to get home. When nearing the south entrance of Marina del Rey she try the engine again only to have it indicate an overheating condition within minutes. Well, it should have, given that the'd boiled off all the coolant earlier in the morning. She'd then call Vessel Assist who would meet her at the south entrance and take her on the hip back into our slip. A few days later I'd check the coolant level, replace what had been boiled off and declare that I couldn't figure out what had happened to make the engine overheat. I need to say here that it never happened when we went over together or when I sailed alone, only when she single handed. As you already know, the problem was that I'd never exceed 3,400 RPM but had never told her about that limit. She would simply put the throttle all the way down to 3,600 RPM when needing the engine in the lighter, late morning winds off the island and end up cooking the coolant out an hour later. Finally I rode along with her one passage over and back with the understanding that I'd do nothing to assist, I'd just observe. The trip over went just fine given that she only used the engine for about 20-30 minutes to get the boat out of the marina. Then came the Sunday return and after close an hour, it dawned on me to look at the engine speed. There it was, 3,600 RPM and the cause of all her woes was evident. We reduced speed immediately and the engine's never overheated since. I'll look around a bit more to see if I can find the 3,000 to 3,400 RPM I quoted earlier today. Stand by (I hope), Glyn
