[RalphG]

I find different engines have different "oil colouring". My 52 Merc engine oil gets dark not too many miles after a change but is does have a lot of short runs and maybe not up to normal temp. But I've got an old Massey tractor with Perkins diesel that I use to handle bales through winter. That one keeps it's oil clean all through the winter. Cold starting and running but I can still see the colour of the dipstick through the oil when I check it. Can't explain that one. I don't worry about it. I'll change the engine oil in my Merc once a year even if it only has a few hundred miles on the oil.