thinking about an oil change on my 62 2.0tdci focus.  halfords do a couple of oils for it.  usually has castrol 5 30 magnatec but that only comes in 1 or 4 litres.    they also do their own brand 5 30 fully synthetic  meets the same ford specs in a 5 litre and its cheaper than castrols 4 litre.  will this oil be suitable for my car.  normally get oil and filter changed 2 times a yr and do about 8 thousand miles town and fast motorway work.

The most common quantity of oil is supplied in 1, 4 or 5 litre containers, unless you want to go industrial and buy a 25 litre drum. Use what the manufacturer recommends in the owners handbook and buy whatever brand you want, remembering you're paying for the brand, all oils have to come up to a certain standard so price would be the deciding factor. Buy a 5 litre container, that way you will have some in hand for topping up should you need to.

Always thought Castrol are a bit mean doing magnetec in 4 litres, luckily mine takes 3.85 litres including filter. Have seen magnetec in 5 litres on eBay but there is fake branded oil around and bearing in mind the importance of it you can’t take a chance.  The Halfords one won’t be magnetic! Does it make a difference? Marketing hype? I don’t know. I can understand the logic but does it make a difference really?

Supermarkets (I have seen it in Asda and Tesco at various times) sometimes have magnetec on special offer. I buy one when it’s cheap so it’s ready for my next oil change even if months away

what does magnatec actually do that others dont.  is it hype.   beating in mind that there ate other well known oils.   i.e   castrol  mobil  petronas halfords etc.  none of those refer to anything remotely mag??

Magnatec is castrols brand name. All other brands of oils are ok to use if they meet the wss-m2c913-d specs

I know for sure Castrol do supply magnatec in 5 litres as well as 4 litre and 1 litre. Also led to believe you can get 20ltre containers too. 

But the above quantities either 4 or 5 litre are rather irrelevant as you need 5.65litres for an oil and filter change on the 2.0 tdci .

So 4 and 2 or 5 and 1.