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Thread: oil
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09-27-2022 04:53 AM #11Senior Member
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- Jun 2007
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- 5,003
Re: oil
FTFD... i drive a slow 1968 41c381
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09-27-2022 07:24 AM #13
Re: oil
Well, yes. Everybody thinks of Detroits as sloppy engines because they were still doing weird stuff like using cork seals for some things into the 2000’s with inevitable oil leaks to follow. They also get a bad rep because of the sportfish guys in every marina with 15,000 hours but won’t do an overhaul who kill every mosquito in a 2 mile radius when they start them up. When properly maintained they’re wonderful engines. I don’t think the modern stuff will give you the same service life. I just overhauled mine, zero smoke, zero leaks. Their internals have very precise and tight clearances. But to your question. I think the real issue is probably the +/- 90 degree angle between piston rings and those air grates in the side of the liners that detroits use as intake valves that’s tough on oils. The factory did a lot of testing and put out a TSB prohibiting the use of multigrade oils.
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Re: oil
The instruction to use particular single-grade oils in 2-cycle DDs has been around since I got into boating, which was in the 1980s. I would imagine that the factory, having more experience with the engines they built, would know better than any other source what oils to run in their engines, and, more importantly, what oils to avoid.
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Re: oil
There is a lot of stuff in CF2 oil that is a must for Detroit 2 stroke engines. So no regular 40w oil will do,
Remember to find that API spec with the rating of CF2.
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09-27-2022 10:56 AM #16Senior Member
- Join Date
- Jul 2013
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- 1,188
Re: oil
As others have said: No multi-weight oil in 2 cycle detroits. It is bad news and will lead to cylinder wall scoring pretty quickly.
Napa has been my source since delo 100 40wt has become all but unavailable in my area.
75118 is the CF2, 5 gal from napa, can't beat the price either, it's significantly cheaper than I was paying for delo 100.
Seems like most coastal napas carry a few buckets of this stock, but they can all seem to get whatever you need in a day or two.
I also use NAPA filters for oil, trans and coolant. So it's nice to be able to get everything from one place.SOUTHPAWS
1986 52C Hull #391 8v92TI
PENSACOLA, FL
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09-27-2022 11:56 AM #17Senior Member
- Join Date
- Aug 2007
- Posts
- 249
Re: oil
Thank you was able to find at Napa much apricated !!
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09-27-2022 12:50 PM #18
Re: oil
I have been buying Delvac 1240 from Summit since 2019, and it has always been a decent price and free shipping.
They seem to be out of stock right now, which I somewhat anticipated, so I stocked up a little bit this summer and have 40 gallons on hand currently.Brett Portzer 1972 Hatteras 43DC331
2019- SUPERNOVA Waterford, NY
1977-2019 CAROL-SUE Baltimore, MD
1972-1977 C.VALPRISANN IV Boston, MA
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09-28-2022 09:52 AM #19Senior Member
- Join Date
- Jun 2007
- Posts
- 5,003
Re: oil
FTFD... i drive a slow 1968 41c381
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Re: oil
It may not be. What's clear to me is that experimenting with boat engines could end up with you needing a very expensive overhaul. Why would you take the risk?
Full disclosure: I have been running a synthetic Mobil in my Cummins marine engines- but that was after a West Coast Cummins shop advised me they had been doing it for years. I would not do it on my own without someone I trusted endorsing it.
Detroit Diesel no longer makes 2 cycle diesels, as far as I know, so my guess is that there isn't any research activity in figuring out which modern oils can safely be used in DDs. If I were running DDs, I'd stick to what most closely matched the specs they originally published. Boat engines give enough trouble and require enough maintenance as is, without deliberately running a non-approved oil.