Why no synthetic oil for marine engines?

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Hello guys. First wanted to say that I own a 1995 Four Winns Sundowner, powered by a Volvo-Penta (slash OMC) 302 Fuel Injected Ford Engine. I purchased it from the original owner, and he had run Penzoil straight 30 oil in since he owned it. Once I purchased it I swapped over the 15w40 Amsoil Diesel/Marine oil for a couple seasons until they came out with their 10w30 Synthetic Marine Oil. I know that the engine calls for 30w oil. After looking through my Volvo manual, it says use 30w oil. Do not use synthetic oil. My question is why not? I have been running the Amsoil in it with great success. Last year I had a riser gasket go on one of the manifolds, so the engine was pretty full of water. I ran the engine quite a bit without knowing there was a problem until I went to change the oil and saw all the water in it. Fixed that, flushed it, back to the Amsoil. The engine ran for several hours towards the end of the season with a ton of water in it, and I never (knock on wood) had a mechanical problem. But back to the original question, people say don't use multiweights in the marine engines because of the unburnt fuel and water that builds in the oil. Yet Mercruiser says use 5w40 oil in their engines. And again, why would the recommend not using synthetic oils? Volvo currently offers synthetic marine oil, and I am wondering that if they were simply behind the ball with oil technology. The engine is 14years old, synthetics were not as common or popular then. Plus, who knows when the first edition of that engine manual was even written.
 
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 Originally Posted By: Jdblya
Yet Mercruiser says use 5w40 oil in their engines. And again, why would the recommend not using synthetic oils?
Where does Mercury Marine say THAT? I haven't seen their latest I/O service books, but last I checked they specified their 25w-40 or a straight 30 for their inboards. The reason Mercury, and many very experienced boaters, don't use synthetics or wide multivis oils in other than newer outboards is that most of the time, you don't need what a synthetic offers, and you don't want a lot of VIIs around. The synthetic oil salespeople may not like to hear that. But that's the truth. FWIW, synthetics have been around since the early 70s, and there were a few trying them on the water even then, with mixed results. Most of us run conventional HDEOs or racing blends, and enjoy gas engine lives of many thousands of hours. These engines run cold, wet and rich. Perhaps in a competition environment or with newbies you'll see full synthetics. Or in a newer outboard or Volvo still under warranty. But that's about it. But if I were you, I wouldn't be focusing on what wide viscosity synthetic oil to use in that Ford 5 liter. I'd be getting compression and leakdown tests and setting aside some repair funds after pumping water for that long. A blown riser gasket is usually very bad news. I'm very surprised you didn't hydrolock it outright. BTW, VP doesn't belong in the same bucket as OMC. The former is a cut above both OMC and Mercury in the I/O hierarchy.
 

Johnny248

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 Originally Posted By: Volvohead
 Originally Posted By: Jdblya
Yet Mercruiser says use 5w40 oil in their engines. And again, why would the recommend not using synthetic oils?
Where does Mercury Marine say THAT? I haven't seen their latest I/O service books, but last I checked they specified their 25w-40 or a straight 30 for their inboards. The reason Mercury, and many very experienced boaters, don't use synthetics or wide multivis oils in other than newer outboards is that most of the time, you don't need what a synthetic offers, and you don't want a lot of VIIs around. The synthetic oil salespeople may not like to hear that. But that's the truth. FWIW, synthetics have been around since the early 70s, and there were a few trying them on the water even then, with mixed results. Most of us run conventional HDEOs or racing blends, and enjoy gas engine lives of many thousands of hours. These engines run cold, wet and rich. Perhaps in a competition environment or with newbies you'll see full synthetics. Or in a newer outboard or Volvo still under warranty. But that's about it. But if I were you, I wouldn't be focusing on what wide viscosity synthetic oil to use in that Ford 5 liter. I'd be getting compression and leakdown tests and setting aside some repair funds after pumping water for that long. A blown riser gasket is usually very bad news. I'm very surprised you didn't hydrolock it outright. BTW, VP doesn't belong in the same bucket as OMC. The former is a cut above both OMC and Mercury in the I/O hierarchy.
I don't know why I said 5w40, I meant 25w40. What does VIIs mean? Are you saying that a synthetic oil would be worse ina cold wet and rich enviroment than a conventional oil? or just that a synthetic would not give you any benifets. And what about the wear protection of a synthetic over the conventional? Finally, I would think an oil that is NMMA FC-W approved would meet marine manufacturers specs for anti-rust and water saturation? I also Ran compression test, twice. Everything looks good. The problem is that I don't know exactly how long I was running the engine with the water in it. All I know is that it was in there.
 
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The typical automotive benefits of a synthetic (such as long drain intervals, improved winter pumpability and high thermal stability) are not as pronounced in marine applications. Chemical stability under high dilution rates is the litmus test for a good marine oil, and more complex automotive synthetics are not necessarily superior in this respect. Esters in particular don't hold up well once you start dumping fuel and water into them. Marine inboards tend to do exactly that. It's been discussed elsewhere, but at moderate OCIs, a good conventional offers no worse wear protection than a synthetic. And there are ample UOAs to support that conclusion. VIIs are viscosity index improvers - polymer additives. Some degrade badly when mixed with fuel and water. That is why straight weights have continued popularity in many marinas. Some marine diesels won't run right on other than a straight weight. The only distinguishing feature of the FC-W approval is a modest salt fog test - not that big a deal. HDEOs have been proven in commercial offshore marine duty, both gas and diesel, for decades. I'll take that over a brief salt fog test. Oils like Delo and Rotella still rule the roost in many working boatyards. I'm glad you didn't nuke your engine.
 

Johnny248

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That is some good information. I really appreciate your knowledge there. I think I may start looking for a new oil to run. So is there any problem with running something like Delvac or Rotella even though it is a 15w40?
 
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An HDEO 15w-40 should be acceptable for your engine. It may lighten the load on the starter at the fringes of the season. But unless it's really getting chilly, a straight 30 will crank over just fine. FWIW, Mercury claims their 25w-40 to be a mix of straight 25 and 40 weights w/o VIIs. I don't use it, but it's an option some like. Other choices are the 20w-50 racing weights, which are more popular with the go-fast crowd. But I don't think you need heavier than a 30 in that engine. I presume you're under 24 feet, so it's probably not working too hard. I think the former owner was doing the right thing, and the engine got to you just fine after quite a few seasons. Why mess with success? If it makes you feel better, sticking with a modern 30 weight is still using a better oil than the last owner did.
 

Johnny248

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 Originally Posted By: Steve S
The 15w-40 Amsoil is one well proven oil. If you are happy with its perfo rmance why change.
The last few seasons I've been using Amsoil 10w30 4stroke marine. I used the 15w40 Amsoil the first 2 years I think that I owned it.
 
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 Originally Posted By: Jdblya
What about Exxon XD3 30w? Is it the same as Delvac oil?
I can't say if it's the same formula as Delvac, but it looks good. It has an API-SF rating, not quite as current as Rotella in a straight weight.
 
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I use synthetics in everything I own except my marine engine (do use in outdrive) My reasoning for this is change interval. I change mine 2 or 3 times a year depending on the use. In my cars and truck I don't mind extending my oil change schedules, but on my marine engine I like to drain and refill more often. Gives me a chance to check out what is going on inside the engine.
 

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 Originally Posted By: rmattingley
I use synthetics in everything I own except my marine engine (do use in outdrive) My reasoning for this is change interval. I change mine 2 or 3 times a year depending on the use. In my cars and truck I don't mind extending my oil change schedules, but on my marine engine I like to drain and refill more often. Gives me a chance to check out what is going on inside the engine.
That makes sense. It is just more of a hassle to change boat oil that car oil =) I know several people who run their oil change in their boats for 2-3 even 4 years at a time.....
 

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Most Walmarts carry Rotella or Delo 30w. If they don't then West Marine does along with the Merc 25w40 which is what I run. The HDEO 30w will give you superb protection and great corrosion resistance as will the Merc oil. The Amsoil ASD 30w is the only synthetic I would consider as it is also a proven performer. Lots of easy choices in a 30w oil. I had a Sunrunner with the Volvo engine and used only Delo 30w in it. Never a problem.
 
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PT1

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 Originally Posted By: Jdblya
It is just more of a hassle to change boat oil that car oil =) I know several people who run their oil change in their boats for 2-3 even 4 years at a time.....
tell them to try a UOA at the beginning of year 2. Then have them get a fluid extractor for $30 and all is good.
 
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90% of my outboard( Mercury 40HP 4-stroke )use is from October to February during waterfowl season. Condensation is a big cocnern of mine. Running in the summer you heat the engine up enough to burn it off. In the middle of January that water can be 28-30 degrees( saltwater use - freezes at a lower temp than fresh )which does not help your condensation issue. I am trying the Amsoil 10W-30 4-stroke oil for the 1st time. I actually want it for the improved cold temperature flow. I change the oil once every year. Actually, the deal Pablo got me on the oil is about what I pay for the Mercury 10W-30 oil. Hopefully it will do well under the extreme conditions I use my motor in?
 
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Outboard engines don't get that hot. Most 2 cycle engines in outboards are set at 140º. The four cycle MAY be 160º. Corrosion is a major concern in ourboard engines, and the MFGs don't think synthetics are all that great at corrosion protection. My 2¢
 

Johnny248

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 Originally Posted By: PT1
The Amsoil ASD 30w is the only synthetic I would consider as it is also a proven performer.
I looked it up, it is actually ACD and it does look pretty good also.
 
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Mercruiser's 25W40 is a synthetic blend and today's (10 years old or so) Volvo engines come with Volvo synth in them right from the manufacturer. The Volvo branded oil that dealers use is also synthetic if it's in a 50 gallon drum or a quart container. It is required for warranty.
 
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