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Old 10-09-2019, 04:25 PM   #5
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City: Rochester, NY
Country: USA
Vessel Name: Hour Glass
Vessel Model: Chris Craft Catalina 381
Join Date: Aug 2019
Posts: 458
If you aren't planning to run long changes and the engines don't run super high oil temps or have other conditions known for being hard on oil, then synth probably isn't worth it.

But if you're going to do oil analysis to see how long you can run, a good synth will usually last longer. And if you have engines that are hard on oil, it can make a bigger difference.

The other factor is cold weather. Personally, my gas engines get Rotella 15W-40 (non synth), as they don't get started in particularly cold weather (under 50* F is very rare), they're not hard on oil and I usually don't put enough hours on in a season to benefit from synth. However, if I were boating in the winter and starting them in colder conditions regularly, I'd go to a synth 5W-40 for better cold start flow (without having to sacrifice hot viscosity to get it).
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