Just topped up my oil as it was slightly below the min mark (oops). Put about 2L of Shell Helix Ultra 5W40 fully synthetic in. Noticed from last svc invoice, that the oil that was put in was 10W50 semi-synthetic. Will there be a problem with mixing these? Also the oil lookes sort of blacker than I expected - (1500 miles since change) - is it normal for the oil to be blackish after so few miles or is this something to do with the semi-syn being mixed with the fully-syn (no miles since this was done today), or a sign of other problems? (Appologies if this has been covered in previous threads but couldn't find anything the same in the time I had).
Shouldnt be a problem mixing them, not something I'd do on a regular basis, but remember most oils are a blend of all sorts anyway. Re. the darkness in the oil, you say 1500 miles, but how long in time ? If you are worried about it, replace it ... it's relatively cheap and easy to do, and it's the best protection for your engine you can do. However, it probably just means that the oil is doing it's stuff ... i.e. keeping your engine clean by holding the dirt in suspension in the oil. It might be that in the last oil change they used a better quality of oil than was previously being used in the engine, i.e. one with more detergents, and the new oil is lifting all the old kak deposits out of the corners of your engine (er, though that in itself can be a bad thing, as it might dislodge a great lump of something, potentially). If you are worried, change it. It's not dear.
