Yes, that's right. The cooler temps with raw water cooling
are specified in order to prevent salt
precipitation in the engine's cooling
passages, but diesel engines run more efficiently at higher temps (180-190F) as with closed cooling systems.
The 4-108, by the way, in the real world is way overrated in terms of HP. Although you see 50HP or 47HP or 42HP in writing, in reality it's a small engine which should be rated in the low 30's, IMHO.
I've lived with mine for 20+ years and love it. Just don't expect a lot of HP from it.