Some of this comes down to age. Back in the 80's and even 70's, Volvo made lots of engines installed in trawlers, etc. Cummins at the time was making the v-block 504, 555, etc. Not the greatest engines, and not supported now, either. The B and C Cummins came out in the mid 80's, and they certainly had their share of trouble. Especially the higher hp B's. They were pretty good at sorting the problems, but it still took a while for the Cummins to get popular in the market. Meanwhile, lots of Volvos were being sold.
In the mid 90's, Cummins came out with the B 370hp and we all joked that this thing was going to be an absolute firecracker. But it was not. The dang thing held up, and now is the gold standard for planing type boats. Still available now as a reman, basically unchanged over nearly 20 years.
The B210 is basically unchanged from the troublesome early 250hp in the 80's, but at its lower rating, it holds up wonderfully. The market realized this and again starting in the mid 90's, it became the gold standard for trawler engines.
The point of all this is that many of the Volvos we like to complain about, and with validity, tend to be quite old.
The Cummins we are so fond of tend to be newer. The old ones were trouble and most are long gone.
I do think the Cummins has a more simple, serviceable and robust cooling system, which is the weak spot on marine diesels- all of them. And the Volvo parts prices are nuts.
So the bottom line still is the rec's go for Cummins. But Volvo did and does make some fine machines. None is perfect.
