what oil to use?

[RWS]

Needing input on what oil to use. We have an 1987 3607 with Merc gas engines with 340 hp which have about 1600 hours on them. We have only had this boat for a year. The previous owner had the boat for 7 years and in his last year he used a high mileage Mobile one auto oil for the yearly oil change. I used a diesel and gas marine grade oil, 15- 30 weight I believe . I have thought for years that using a synthetic oil in older engines could lead to oil leaks.What would you recommend we use? Compression check when we bought the boat showed 140-150 on all cylinders on both engines. What should we do for oil this season?

[tomschauer]

I use mobile 1 in all my gas engines, including of course my merc 7.4's.
Many other on this site will swear by the shell rotella.
I have stated on other posts, that I believe any good quality oil, changed at regular intervals will be fine for recreational marine use. The Mobile 1 or any synthetic oil, will not cause leaks. Time and operating, or sometimes more so, non operating conditions (gaskets and seals drying out from lack of use) cause leaks, not the oil itself.

[RGrew176]

I have an 81 3007. My mechanic uses a synthetic blend oil. So far no issues.

[Tireless]

I use Shell Rotella (T4-15W40) in everything, including the gas burners.

[SplashyLady]

X2 for the Rotella 15-40. I think the 40W high-end helps with engines that are over 500-600 hours - especially big blocks.

[g36]

Another shell rotella user here

[ColRon]

For me it's either Rotella or Mobile one. Used Rotella in my classic Corvette after an engine rebuilt and Mobile one is the factory fill in both the admirals and my daily driver. I also use Mobile One in Escape Plan's 454 crusaders.

[bud37]

Source of the post Needing input on what oil to use. We have an 1987 3607 with Merc gas engines with 340 hp which have about 1600 hours on them. We have only had this boat for a year. The previous owner had the boat for 7 years and in his last year he used a high mileage Mobile one auto oil for the yearly oil change. I used a diesel and gas marine grade oil, 15- 30 weight I believe . I have thought for years that using a synthetic oil in older engines could lead to oil leaks.What would you recommend we use? Compression check when we bought the boat showed 140-150 on all cylinders on both engines. What should we do for oil this season?

In general, oils specified as " high mileage "....may have seal conditioners etc to cut down on oil leakage on older engines. There are lots of good choices, but if you change ,keep and eye out for leakage , considering why the previous owner used high mileage oil.

[throwback2]

Rotella and mobil 1 filters

[Midnightsun]

Rotella T4 15w 40 in all my previous gas boats, my Carver, my ragtop summer only car and the PWC. Always buy it when goes on sale for the 5 gallon pail as I go through 15 gallons a year.