Oil weight for 40 Merc 4-stroke?

My manual is at the cabin. I cant remember if it calls for 10-30 or 10-40 or even 5-30. Thanks.

My 15 HP (around 2005 model) says right on the back of the engine (under the cowl) that the recommended oil is 10W-30 under 40F and 25W-40 above 40F. I believe I have run 10W-30 all year with no issues.

The motor is in the same location as the manual. I would like to buy my oil before I go back. I have changed the oil in this thing for 8 years running (Mobil 1) and cant remember!

Year?

06. Got it. Just got back from a Merc dealer. 10-30.

Just curious Suzuki…If you change it every year why do you use synthetic? Is it just a “want the best for my motor” thing or another reason. I have a 50 merc 4-stroke and have always used conventional 10W-30 but would consider synthetic…

I’m a big believer in synthetics for longevity and hard duty. I’ve been using Mobil 1 for extended miles in many vehicles for a lot of years. With that kind of experience comes trust.

I especially like it in my Merc 40 because the pontoon is in the water all summer so one oil change sees a lot of service. I’ve been running that 40 up and down my flowage weekend after weekend at full speed for 8 seasons now and it still runs like new.