Re: Confused about which oil weight to use
Good day DixieJulie
Once you eliminate the simple things as mentioned above there is something to think about...
Since it is raw water cooled and salt water.... its a bad combination for any cast iron or cast steel (doubtful) engine cooling system. Even with freshwater flushes it still builds, just slower.
Not trying to alarm you and I do not know how old or how many hours are on you engine... but if its older there is a good chance of rust scale buildup inside the head's cooling passages as well as the cylinder walls cooling jacket. This restricts the flow gradually over time and they start running warmer... when it gets past the point that the thermostat can compensate by flow increases they will start to over heat. The fact someone removed the thermostat to try and increase flow may be an indicator it maybe reached and exceeded this point. In extreme conditions actually eat through the cast iron in the head into the combustion chamber or the outside. I have an old VP MD7A... that was raw water salt water cooled out of FL... When I dissembled it, you wouldn't believe what those cooling passages looked like... 30% flow at best.
But you said it was an intermittent overheat? Could be you haven't quite reach the junk point, but it could be an indicator of scale breaking loose and causing a downstream temporary blockage. If it were I experiencing this shortly before a long sail... I believe I'd be pulling the head and seriously inspecting all the cooling system, but I am mechanical and have been inside a lot of engines in my time. Usually a head pull is not all that hard or costly and you can determine many things on its condition (including the valves and cylinders).
If you do or have it done... any linage you open... replace with new... on principle. Some shops will do that by default... some not. Make sure they do. Cheap insurance.
If its only the head... a replacement head will solve part of the problem. The cylinder jacket is a bit harder and would require a total dis-assembly and cook out... and then pressure tested. That gets into major money as its a total rebuild. The problem long term is raw water cooling.
The boat I just purchased last fall is raw water cooled. Since I am swapping engines anyway I will convert to freshwater cooling and a heat exchanger just on principle. If you plan to do all salt water sails I would seriously consider this... especially if you rebuild or replace your current engine.
Before leaving on a long sail away from normal service availability... its good this happened in a way, as you can address it now.
1980 Seafarer Swiftsure 30
1978 Bayliner Buccaneer 270 (now sold and being restored in FL)
1962 SeaMac 14' Plywood Runabout, mahogany decked, with 1959 Evinrude 35 Big Twin (owned since age 17, I'm now 60)
Last edited by dem45133; 08-04-2013 at 12:07 PM.