So as I'm tweaking things on the second summer of our "new to us" boat (the '97 300DA)....I'm getting bothered by what I think is high oil consumption on the starboard engine. Brief history/background. *Purchased boat Spring 2018. *Last summer, and this summer, the starboard engine is still thirsty for oil. Last year I noted the original owner has used 10-40 oil. I changed oil twice last year with 25-40 Quicksilver oil...hoping the thirst for oil would slow down with the proper thicker stuff. It didn't. Plus look OK. No drips in the bilge, it's not a leak. Engine hours, ~570 port, ~660 starboard. 5.7 260 hp Mercruisers. I topped off oil before a trip to Greenport LI a few weeks ago, when we returned, the ~4 hour cruise consumed 1/2 qt of oil in the starboard engine. Probably not even an 1/8th of a qt in the port engine. My cruising speed for most of it was 3300-3400 rpm. I rarely take her about 4k rpm...probably twice this summer, and not for long. Engine temps decent...165-170. I have read that PCV valves can affect oil consumption. I "think" mine are just elbows there with a hose to the flame arrest/air intake...but will check. She gives nothing visible for exhaust...no smoke. No oil sheen in exhaust water existing. There is a very slight blackening around the starboard engines above water exhaust exit...very slight, compared to the port side which is nice 'n clean white. I'm fearing valve seats I suppose? Not sure what a top end job runs. ugh. Until THEN..has anyone in a similar situation found some relief in going with a thick straight weight? We don't run her in cold weather, she's not year round up there...up on the hard during winter.