15w40 is pretty heavy for a samurai.  I'd stick with either a 5w or 10w oil.  Personally, I run 5w30 in mine (kansas city, mo area).

My owners manual for my 87 Sami says to use 15-40. I'm located in AZ and thats what I'm using.

As you know the Delo is good oil, use it and add a bottle of marvels mystery oil to it to thin it a bit and help lubricate and clean you engine too. Sounds like a win win.

15w-40 is fine in warm weather, it's a little heavy in the winter, that's when I
switch over to 5w-30, remember the first # is the real weight of the oil, the
second # is the simulated weight when the polymer additives lengthen out
and try to make the oil act thicker, even tho it isn't.

The best oil for lubrication is 30W not multi-grade, but most people these
days don't have the patience to wait for the engine to warm before driving,
so we use multi-grade oils so our engines survive to cold drive.

In the summer I use 20w-50 because the 5w-30 would cause the light to
come on at idle when it gets to 110* outside

Wild

40 w is too heavy for your samurai. Go for 10w its by the recommendation. Check out for online documentation or the dealer for a good idea. Run your Samurai with this grade of oil in cold regions will ruin the engine..