I've used a Mann oil filter and the and book recommends 5w30. I rang my local Honda dealer and they said they just put castrol 5w30 fully in it at service.
Well you can put it in and try it. You might get a knocking engine or slightly more tappety. Thicker oil provides better wear protetcion on old engines, i feel 5/30 is too thin and your moving quite a long away from the original oil grade for these engines. 5/40 is the middle ground if you want fully synth oil.
Its the specification that matters not the label on the can.
You can pay an awful lot of money out for oil, following the marketing hype. Of course if it makes you feel better, and you have the money, then why not.
If you live anywhere near Chesterfield or Bolsover, I can recommend Aztec oils at Bolsover. They buy their oil products in huge bulk containers and then bottle it themselves - with a label that breaks down all the specifications it meets or exceeds. They also sell it in bulk to garages and other users.
For example, I think a five litre pack of 10w/40 semi synthetic, which meets BMW, Mercedes, VW blah blah ..... etc costs about £10
Of course the garage will charge you about £50 + vat.
Honda service history that came with my car states 5w30 magnatec from 2008 onwards .... eek... apparently that's what Bedford Honda put in them as standard.
