I have a JP2 in my narrow boat, and it's coming up to end of season oil change time. I've always used sae 30 grade oil, but, while checking oil prices, I came across some sae 40 grade oil which is designed for "summer use and will help quieten engines" or words to that effect. My engine is always very quiet on start up, but as it warms up, gets a bit noisier. I was wondering if I would be likely to encounter problems if I filled with 40 weight oil this time. Would it possibly harm the engine in any way?
The engine was rebuilt by me 20 years ago, with new bearings, etc. and has not had a great deal of use since then, so should be in good condition internally. I would anticipate it being more difficult to turn over when cold, but I don't use the boat in the winter(I'm embarrassed to admit) so that would not be a problem.
Any thoughts and opinions would be much appreciated. Jack