_captiva@att.net_ (mailto:captiva@att.net) writes: I have a 42' Bristol Offshore trawler with DD 453n's. Seems I don't see many mentions of these engines. How long have you been operating them? What RPM's? What transmissions do you have? How often between oil changes? What oil do you use? Don: Detroit Diesel (DD) 53 series engines all use the same fluids unless a unique transmission is utilized. I've had 3-53's and 6V53's . You should follow DD recommendations by using a 40 weight oil like URSA that meets mil spec 2105E (E is the latest, I think). Many other brands meet DD specs as well. These are wet liner engines so it's best to use the recommended antifreeze, maybe its spec TP329 or something very similar. Anyway, the container will say something like "Meets Detroit Diesel specifications". 100 to 200 hour oil changes are likely fine, longer if running easy; I just posted about changing 6V53 oil at about 175 hours and at that interval oil tested "ok". At your next oil change, have your oil tested and see the test results. My Borg warner transmissions used hydraulic fluid, others likely vary. If your engines turn the rated 2800RPM, running them at 1900 to 2100 will be EASY on them. I ran some 6V53's for 22 years at 1900 RPM and the only thing I did was have injectors rebuilt once. And one governor bearing. Moderate RPM reduces fuel consumption and extends engine life significantly. These are great engines but tend to have a relatively loud whine which lower RPM's also helps tame. Rob Brueckner 1972 Hatteras Yachtfisherman