I had a service carried out on my Peugeot 207 sport 1.6D, and as part of that service the oil and filter was changed. After two days I checked the oil and found it to be black. Is this normal? My first reaction was that the oil had not been changed, so I returned to the garage and they said this was normal because when draining the old oil some always remains in the engine and when the new oil is added it mixes with the old oil and causes this appearance. Also could you tell me if my car has a drain plug fitted to remove the oil, or is the oil sucked out of where the dipstick goes?