Recentley I asked a very experianced mature marine meckanic for assistance in sorting out my impellor on a 15hp mariner 2 stroke o/b.He sorted it out by getting me the correct impellor, I had been sold the wrong one, and that was from a mariner agent. We found at that time that the thermostat needed replacing- it was naff. It was taken off.He told me that a replacement would be about £40, and adviced not to bother fitting one as "British waters are warm enough", those were his words.I couldnt argue as hes forgotten more than Ill ever know, but it got me thinking and thinking till I gave up then thought Id ask on this site what do you reckon gents? Spend the money or leave it as it is?