40W for 260 Mercruiser

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350 Chevrolet flat tappet cam Boat is only used hot summer months and Mercruiser recommended straight 40W for ambient temps above 60 degrees F. I have fairly easy access to Rotella 40W, Delo 100 40W and Delo 400 40W. I heard that the Delo 100 has less ash than the 400, is less ash better for my use? Which of these oils has the most zinc and additive protection for the flat tappet cam? Which of these three oils would you run? Thanks.
 
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The engine will work at high rpm and load enough where any deposits should be blown out. I would use the Delo 400 or the Rotella . I used Delo 400 15w-40 when I had my boat because it was cheaper at Costco and Walmart at the time ,the oil worked great . Great results upon tear down inspection .
 
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 Originally Posted By: BUBBA0420
What's wrong with the Merc 25-40 Oil which is the first recommendation
Its an arm and a leg and not too easy to find. 40wt will be fine!
 

Duplex

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Thanks for the replies! Got a few gallons on Delo 400 40W now so will run that this summer. The boat is run pretty hard and it with the heat down here would really like to stay with a straight 40W as opposed to the 15W-40. The Mercruiser 25W-40 from what I understand is a half and half mixture of straight 25W and straight 40W so works out to only about a 32.5W. Can get the Rotella 40W at O'Reilly's for $13.99 per gallon so will probably end up running that. One more question, does the Rotella straight 40W have basically the same zinc and additive protections as the Rotella 15W-40? Thanks again.
 
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I run my boat hard. I flat out run 5200 RPM for 30 minutes to the crabbing grounds. Then, I work crabbing gear trolling for hours with quick high RPM runs back to the beginning of the gear. The motor never shuts off for 8 hours. That my friend is hard on an engine and engine oil. I think the DELO will serve you well.
 

PT1

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Any of the HDEO 40w will work. Pennzoil Marine 40w is available at many WalMarts as is the Quicksilver 25w40. All are under $5/qt.
 
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Mercruiser 25W-40 is a blend; as most marine MFGs don't suggest full synthetic. Reason being synthetic does't protect against corrosion as well as conventional oil does.(so they say). IT IS NOT a mix of straight 25 and straight 40. If you insist on going thicker; mix some 15W-40 with that straight 40. A 25W-40 is a 40 at operating temperature.
 
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I agree that any of the HDEO oils will be very close their marine formulas and will do a great job.
 

PT1

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 Originally Posted By: dwendt44
Mercruiser 25W-40 is a blend; as most marine MFGs don't suggest full synthetic. Reason being synthetic does't protect against corrosion as well as conventional oil does.(so they say).
From what I understand that is true. I do know the Merc 25w40 does cling on for a very loong time as when I start my boat at each Spring launch it doesn't knock at all. That really amazes me.
 
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What about the Sierra Marine 25w-40? Any info on that oil? Aimed to be a copy of merc 25w40 but is it good?
 

PT1

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 Originally Posted By: lars11
What about the Sierra Marine 25w-40? Any info on that oil? Aimed to be a copy of merc 25w40 but is it good?
Haven't see that anywhere.
 
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 Originally Posted By: dwendt44
Mercruiser 25W-40 is a blend; as most marine MFGs don't suggest full synthetic. Reason being synthetic does't protect against corrosion as well as conventional oil does.(so they say). IT IS NOT a mix of straight 25 and straight 40. If you insist on going thicker; mix some 15W-40 with that straight 40. A 25W-40 is a 40 at operating temperature.
M-1 20W-50 V-Twin and M-1 10W-40 4T Motorcycle oils are loaded with corrosion inhibitors. So is Amsoil's 15W-40 marine/diesel.
 
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The Delo 100 that you mentioned is not rated for a gasoline engine. I would not use it although I don't know if it would hurt anything. From the Delo site "The SAE 30 and 40 grades are also specifically recommended for use in two-stroke diesel engines requiring highly effective control of wear and deposits. Chevron Delo 100 Motor Oils: • meet API Service Categories — CF-2, CF, CD-II1, CD1 • comply with Detroit Diesel Corporation twostroke engine recommendations, including the 0.85% ash maximum limit for Series 149 engines."
 
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If you run a HDEO corrosion will be a non event. Commercial marine companies run HDEOS in the automotive marine diesels. That fact alone seperates the readers from the knowers.
 
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