I find the Opie Oils site really helpful. Just tap in your registration no. and the site will bring up a range of oils suitable for each model. You can combine the oil with the correct filter in what they describe as a service pack which should automatically include the correct volume of oil for the engine. They will often pop up on the site offering discounts if you are lucky. From the selection of oils they recommended I choose Millers Nano-Drive 5w-40 for No146's guzzle this year and ordered the filter at the same time. Easy!

Andrew.