Mercruiser 350 Mag

[arthura]

In a 31 foot sundancer with 350 Mag engines, up to what RPM can these engines be run at for long spans of time? I am planning a week long cruise, with long stretches of open water to cross daily in the upper great lakes (100-150 nautical miles per day). For these exposed stretches I want to run on plane if possible, to get across asap. Is there a general rule about the best range of RPM settings to use to get a good planing speed while preserving engine life, and also optimize fuel and lubricant consumption? If I ran the engines at, say, 3200-3500, how long can I safely do so, and how often should I check the oil levels? Is there anything else to routinely check when pushing the engines at those rpm levels? My two fears are running out of fuel along the way and over-heating my engines, while trying to get across open water stretches.

 

[Chris Dauth]

Assume for a moment that your engines can achieve the recommended WOT rpms as per the manufacturer. Should be in the range of 4750 to 5000 rpm for the MAGS. (if I remember correctly)

Then, you should be able to run at your 3200 – 3500 rpm all day without any harm.

I often cruise the Queensland coast here in Australia, up to the Barrier Reef, with hops of 200nm a day and the 383 stroker just loves 3500 rpm. This gives me about 25 knots, depending on sea conditions, with the boat fully loaded.

If you are doing extended cruising, I strongly recommend the installation of some form of fuel monitoring computer and then get to know exactly what your most economical speed is and how far you can go on a tank of fuel.

I usually carry 2 gallons of lube oil on a trip and check the oil levels every day and top up as necessary. A full sump means cooler oil due to the resonance times.

Enjoy your Trip !!

.

 

[terminaldegree]

I would agree with the above post. Be sure the cooling system of your boat is in good working order (water pump impellers less than a year old- carry a spare with you, a couple of quarts of oil, a quart of transmission fluid (or drive oil if you have sterndrives), hydraulic oil for the steering system (if you have one) or ATF for automotive-style power steering. Before embarking on the trip, check around the engine room for leaks while running and immediately after running. Check your bilge pumps, VHF radio, basic tools, safety equip, etc.

If access to your engine room is easy, I would probably check things "under the hood" before each long day of running, and at least once per tank of fuel if it isn't...

Fuel monitors will sometimes help to point out upcoming mechanical problems that aren't yet serious. Knowing a "baseline" fuel burn for each engine at cruise is a good reference point to have. You can do this manually as well, but it takes a little more effort/calculation... Our 340da with 350 mpi mags (B3 sterndrives) would burn roughly 10 gph @ 3200 per engine.

When figuring fuel range, keep in mind the engines can't use every gallon of fuel in the tank (I would not count the last 10 gallons in each tank as "available fuel"), and you should leave a ~20% "reserve" in your calculations to compensate for a worst-case scenario- outrunning a storm at high speed (burning far more fuel), needing to alter course slightly for the sake of a smoother ride, or sudden mechanical issue causing a higher than normal fuel burn.

The feeling of boating all alone, out of sight of land, is exhilarating for me because I do it so infrequently. Just plan as much as you can in advance.