I have a 1973 Ford 351 Windsor engine with low milage but being a marine engine it's under contant stress and strain. On start up it'll blow some blue smoke, and the oil gets dark pretty quick. I do two oil changes pre season, spring and fall, and add Lucas oil additive to suppliment. Being a marine engine oil changes are done through the dip stick with and electric pump for extraction. This seemed to help at first, but now the engine will run fine (temperature wise) at idle, but under load it begins to slowly overheat. The marine mechanics have tested the engine and tell me that the engine is fine as there is only a 5 degree temperature difference between the front and rear of the engine. They suspect a faulty temp gauge, but to me this engine feels moticebally hotter than the port engine for the same duration. I personably believe that I have a build-up of oil pan sludge (because of the Lucas oil additive) which is causing the engine temp problem. And since I can't remove the oil pan plug because of inaccessability I can't get gravity to remove the sludge build-up.
What can I use to thin the sludge build-up so all can be extracted via the dip stick?