A little pamphlet in the owner's wallet suggests Castrol Magnatec 10w-40 (which is a semi synthetic petroleum based oil) I already have some. I have used this oil for many years on previous cars. The pamphlet goes on to state that Castrol SLX 0W-30 (which is a fully synthetic oil) is recommended for ultimate protection.
I know semi synthetic petroleum based multi grade oils have additives to make them achieve the higher viscosity rating at normal engine operating temperatures, and that over time these additives degrade and pull the operating temp viscosity rating down.
I don't know whether to use Magnatec 10w-40 and change it every six months or use SLX 0W-30 and change it every 12 months. Mileage is an issue as car will be used for short trips of less than 5 miles (bad), with no motorway driving, so would probably qualify for the severe service schedule (< 6k miles pa). SLX appears to have been replaced by Castrol Edge Professional, and is £10+ more than Magnatec 10w-40.
Since car wouldn't used around Siberia I don't think I need viscosity protection down to -30 degrees with a 0W or 5W.
Haynes manual says 5W-30, 5W-40, 10W-30 or 10W-40.
Honda Owner's manual says 0W-20, 0W-30, 0W-40, OR 5W-30, 5W-40, OR 10W-30, 10W-40.
The graph on page 286 of Honda Owner's manual is not very helpful in trying to decide on a SAE 20, 30 or 40 oil. But I would have thought that a higher operating temp viscosity number would be better, the warmer the country.