Most small
marine diesels do not use air filters. The reasoning is that they do not operate in a dusty, dirty
environment and the filters are a complexity that is simply not needed.
My 30 yo Volvo with 10,000 hours never had one. My previous
boat had a
Westerbeke that ran 9000+ hours with no air filters. An Onan
generator ran 8000 hours, no filter. My
current Whisperpower
generator has no air filter. Are you seeing a trend here? In all these the engine did not come with an air filter because the design engineers did not feel it was needed, and apparently they were right. Put the same engine in a farm tractor, and of course an air filter is 100% required.
On issues like this I tend not to second guess the engine
builder. Of course people will happily sell you an after market filter. But take what they say about the “need” for it with a grain of
salt. They are selling something.