[AndyV7o]

Im not a 240 owner, but 0w40 all year should be fine in terms of viscosity (I wouldnt use a w30) as 0w cold is still thicker than 40w hot, which is what you have at full temp.
However, what is the year? If its between 70's and 90's you dont want to be running modern oils in it, they dont have necessary additives which are needed in older engines, thus will shorten the life as wear will increase. In older engines you need an old spec oil to properly protect them, the most modern you ought to use is a basic A3/B4 with very few other, older approvals/specs, otherwise investigate 'classic oils' for cars of that era.
You should also be ok with a basic 5w40 synth such as Gulf formula G, Fuchs Titan Supersyn, Shell Helix Ultra, which have older specs, a 5 still flowing better than a 10 when cold, but correct vis when hot.