What viscosity oil are you guys putting in your I/O? I have the (2005 year) 5.7L Volvo Penta (280 HP) which is basically a 350 Chevy. I changed the oil myself 2 years ago and honestly cannot remember what I used other than it was Mobil 1. I have the engine manual and in the chart it lists 30W, then 20W/50 and then 15W/50 for outdoor temps 32 degrees and warmer. You can't get Mobil 1 in 20W/50 but you can in the 15W/50. Here's the kicker though.....to the right of that chart in my manual it says:
"Use single viscosity oils in markets where available. The use of multi-viscosity oils such as 10W-30 and 10W-40 is not recommended unless single viscosity oils are unavailable."
Straight 30W is what I use in my push lawnmower and I was also told this weight oil does not have a detergent and I shouldn't use it in a big engine like I have.
So what should I put in it?
I'll let others chime in here too but we always used Valvoline SAE40 Racing Oil in our previous 454 I/O runabout. We used dino oil, not synthetic. Nothing against Mobil 1 but the recent buyer insisted on a compression test before signing off and while only ~500 hours, all cylinders read
extremely well. Although cost difference between the Valvoline Racing Oil and Mobil 1 may be minimal, if anything - just maybe another option if you can't find the viscosity you're looking for which I agree is important. Note that we are further south than you (St. Louis area) and didn't run the boat in cooler temps, if you want to take that into consideration.
And on many or most motors, you may not want to run synthetic in anything that isn't fully broken in (to ensure proper ring seating) but double-check with manufacturer specs on that. In the end, since you likely are more concerned about mechanical failure (probably would be due more to abuse than you wearing it out and since you asked this question, doubtful you are an 'abuser'), I'm sure either is fine as long as you are using a quality product. Again, maybe another alternative for a non-sythetic.
FYI - I always use Wix filters (also can be purchased repackaged as NAPA Gold, the high end Car Quest version, etc. - should say so on the box). I cut a new Fram in half years ago and wouldn't put that on any engine, assuming they haven't significantly changed their design but that was enough for me. I run my vehicles 300k miles plus (pretty much until they are impractical for my use, not because they are shot), all the time never using synthetic (again, not that there's anything wrong with that and can understand the benefits for certain users). Just saying that a quality filter can make a difference which you may have already knew. Of course, the OEM manufacturer filter is good too and wouldn't discount them but if you are considering or want another option than OEM, I just became a believer over the years in Wix oil, transmission, fuel, etc. filters. To me, they are the 'Bennington' of filters
and my vehicles are proof positive.
