what motor oil should I use

bruceb58

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Personally I like the 10-40 oil choice. The lighter cool temperature viscosity is now all the major motor manufacturers recommend since it ensure early oil delivery when you start your motor, they have mostly gone to 5-30. It will also suction out a lot easier than 25-40 using a vacuum unit.

I keep an eye out for the 1/2 price NAPA oil filter sales and buy a case of their NAPA Gold filters, made by WIX. The good stuff.

Volvo recommends not using 10-30 or 10-40 oils. Same exact engine blocks as Mercruiser uses. Use the viscosity that the manufacturer says to use....easy peasy.

volvo_oil-1.jpg
 

HT32BSX115

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And I do recall reading about some additive that diesel engines need for soot control, maybe not being good for gas engines. Who knows.
Yeah. I have "heard" that too. It's another old wives tale IMHO. All of the diesel "rated" fleet type oils also meet current gasoline engine API ratings. I know of no one that has EVER had an oil related failure in a gasoline engine from using and CD/CE/CF/CG/CH/.........etc oil that also was additionally rated at whatever the current gasoline rating was.
Additives that help to keep soot in suspension do not make the oil any more "detergent" than any other gasoline (only) rated oil.

And yes. NO ONE should EVER "flush" any old engine by diluting the oil with kerosene, diesel, gasoline, Marvel Mystery oil, ATF, Seafoam, Super Secret Owl Snot, or any other snake oil.

That could absolutely cause sludge to break off and clog the oil screen.

If it broke off AFTER the oil filter in an oil passage supplying a main, rod or cam bearing, you could starve that bearing and cause a bearing seizure.

As usual, (And I just LOVE oil threads!!!) these threads ALWAYS end up being: "Here's what I use and I have never had a problem........."

Back the OP's question......

what motor oil should I use

October 2nd, 2017, 06:40 PM


My 1996 4.3 l mercruiser calls for an SG grade oil.
If you do not want to use what Mercruiser currently suggests using, you can safely either use any oil on the the chart Bruce posted above........OR you can just about use any oil on the Autozone or Walmart shelf (near the correct viscosity as required)

Understand 0W30, 5W30, 10W30 synthetic oil IS SAE 30w oil at 100C............ 0W40, 5W40, 10W40, 15W40, 20W40 and 25W40 SYNTHETIC IS 40 wt oil @100C

Synthetic oils DO NOT thicken when cold like NON-synthetic straight wt oils do.....which is why you might want to use them in very cold temps all the way down to -30F.......although if it's -30F, your engine will start and run great......your boat will be literally FROZEN IN PLACE and if you're raw water cooled, the engine will over heat quickly......the raw water pump won't pump solid ice!!!!!


NON-synthetic 5W30, 10W30, 15W40, 20W50 etc...... ARE 5wt, 10wt, 15w and 20w oils (respectively) and use viscosity improvers to get to the higher visc at 100C

When the VI-improvers "wear out" the oil will become thinner. (because they ARE thinner without the VI-improvers)

Cheers,


RIck
 
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Jcris

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I appreciate all the conversation and experience here,
So after much reading and some learning I've concluded that using what the manual recommends is the best/safest choice. Shocking development there. Easy enough, or so I thought. The Mercruiser operation and maintenance manual for stern drives and inboards says I should use Quicksilver 4-cycle marine motor oil. It further recommends a straight 30 weight or a 20/40 multi viscosity, both with an SG rating. It says nothing about synthetic vs conventional formulations. Given this manual was written in 1995 and presumably motor oil formulations have changed since then I must ask. What is currently recommended? Is the Quicksilver marine oil a blend? And does that mean it incorporates synthetic as well as conventional oils? I'm trying to determine the best choice for a motor that has less than 1500 hours on it and is currently using 10w/40 Valvoline automotive, detergent type oil. I change the oil and filter once a season, so cost is not the most important issue.
 

Lou C

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The Merc oil is available in a conventional version and a syn blend version. Either will work well in your engine. The advantage to me is that:
​1) no VI-improvers are used, so it will not lose viscosity
​2) meets the NMMA corrosion resistance test

​Yes it costs a bit more than Delo or Rotella 15w/40.
​Just as a data point here is a brief summary of 2 oil analyses I did with Blackstone Labs:

Merc 25/40, sampled at end of season '15:
​SUS viscosity 81.1 Should be between 68-78
​cSt viscosity 15.79 Should be 12.4-15.3

Chevron Delo 400 monograde 40 sampled end of season '11
SUS vis: 67.0
cSt vis: 12.16



​People like to debate oils all the time, very few actually test one against the other. And this is why, I use the Merc oil; you can see, it held up even better than a diesel rated straight weigh. OK the nay-sayers can line up, just provide your test results please, lol.....
 

Rick Stephens

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The Merc oil is available in a conventional version and a syn blend version. Either will work well in your engine. The advantage to me is that:
​1) no VI-improvers are used, so it will not lose viscosity
​2) meets the NMMA corrosion resistance test

​Yes it costs a bit more than Delo or Rotella 15w/40.
​Just as a data point here is a brief summary of 2 oil analyses I did with Blackstone Labs:

Merc 25/40, sampled at end of season '15:
​SUS viscosity 81.1 Should be between 68-78
​cSt viscosity 15.79 Should be 12.4-15.3

Chevron Delo 400 monograde 40 sampled end of season '11
SUS vis: 67.0
cSt vis: 12.16



​People like to debate oils all the time, very few actually test one against the other. And this is why, I use the Merc oil; you can see, it held up even better than a diesel rated straight weigh. OK the nay-sayers can line up, just provide your test results please, lol.....

Hard to argue with that. Dang it..... thought these oil threads were supposed to be a war zone or sumthin.
 

alldodge

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I would like to know of anyone which has done regular oil change maintenance (not oil specific) which has had an oil related failure
 
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I would recommend 10W30 if you are planning on going during the colder months, synthetic is always the better oil but you usually want to use the same oil you have used previously.
 

Jcris

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A valid point AllDodge,
Just regular maintenance "should" eliminate a lot of problems and probably goes a long way toward reducing the differences between premium oils.
 

QBhoy

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I'm confused. I thought the manual called for 25w-40 ? Where did 20w-40 and 20w-50 come from ?
Who doesn't love a good oil thread ! Haha.
 

HT32BSX115

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Even if you use the most expensive stuff, it's not all that expensive on a per year (or per hour basis) when compared to the gasoline you put in your boat for an entire year.

My last boat ( 66 Mercruiser 150) went 39 years getting the oil changed every year (or in some cases every other year). The hour meter failed in the 80's at about 1500hrs...... I sold it in 2005. It still ran pretty good! It got a different oil every time it was changed.

I think we all may worry about oil a bit too much. Just check the level regularly and change it and the filter before winter layup with whatever makes you happy. There's a LOT of other things that one should worry about :thumb:
 

QBhoy

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The Merc oil is available in a conventional version and a syn blend version. Either will work well in your engine. The advantage to me is that:
​1) no VI-improvers are used, so it will not lose viscosity
​2) meets the NMMA corrosion resistance test

​Yes it costs a bit more than Delo or Rotella 15w/40.
​Just as a data point here is a brief summary of 2 oil analyses I did with Blackstone Labs:

Merc 25/40, sampled at end of season '15:
​SUS viscosity 81.1 Should be between 68-78
​cSt viscosity 15.79 Should be 12.4-15.3

Chevron Delo 400 monograde 40 sampled end of season '11
SUS vis: 67.0
cSt vis: 12.16



​People like to debate oils all the time, very few actually test one against the other. And this is why, I use the Merc oil; you can see, it held up even better than a diesel rated straight weigh. OK the nay-sayers can line up, just provide your test results please, lol.....

Lou....hard to argue. Excellent stuff, but was the 25w-40 Merc quicksilver oil the newer synthetic blend ? I hear this hold up well on testing.....but the older 25w-40 does not. There is a similar post somewhere on here showing huge detriment and deterioration after end of season testing.
 

Lou C

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Nope the Merc stuff I used was the basic 25/40. If someone had different results, maybe we didn't get the whole story.
There are other factors that will be associated with the oil not holding up well. As in: running too hot, getting water in the oil, running wide open for long periods of time, using poor quality or low octane gas, or fuel dilution of the oil. All those things can affect oil life. One rule of science, is you keep all other factors constant and only vary the factor you are trying to measure. So my tests are same engine, same operating conditions, same temp, grade of gas, etc.
 

Lou C

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Oh and what adds to the confusion; when Volvo recommends 10/40, it is a SYN oil not conventional. A Syn oil can span that range with no VI improvers, conventional cannot. It's the VI improvers that eventually cause trouble....
 

khe

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I sent a sample of Rotella 15W-40 oil from my boat engine with 55 hours on the oil to Blackstone Labs for analysis. They reported back that the TBN value was 3.8 which needs to be greater than 1.0. A search on Rotella 15W-40 oil turned up the base value was 10.1 so there was plenty of antiwear additive left. The metals content of the oil was below the average for my type of engine.

I would conclude that the Rotella 15W-40 oil is doing a good job of protecting the engine. I plan to have it tested when this oil has 75 hours on it next season to see where the TBN value is.
 

Lou C

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Also post up the viscosity ratings as well, that would be interesting to see. If they are good, then that proves it is a valid choice if you don't want to spend the extra few bucks for a gallon of the Merc oil.....
 

Jcris

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Interesting post,
I'm curious weather or not going to a full synthetic is a good choice? I don't know the maintenance history. All I can say for sure is the oil used last time was 10/40 conventional Valvoline. It does not use oil and there are no leaks anywhere. But, I've only had this boat for 2 seasons which all told equals less than 50 hours. My main concern is that the last two times I've noticed some smoking on cold start. Not a lot but enough that I thought an oil change would be prudent. Since the maintenance history is clouded, do you think I should have an oil analysis done? If so who is the lab of choice?
I just checked out Blackstone labs online and ordered one of their kits. I'd like to send off a sample right away not using their sample bottle. What are you guy's using?
 
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Rick Stephens

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Hard for me to believe anyone sweats this. Good oil, within the designed operating range of the motor, will lubricate it and do a very nice job of it. Synthetics bring interesting benefits to many engine applications, but one of the biggest is oil life, and we don't run boat motors long enough in a years time, with an annual oil change in the plan, to benefit at all from that. Nor from higher temperature resistance of synthetics, since boat motors have virtually unlimited cooling and run on the cool side anyway with most of them being open systems with no pressure.

I tend to use a multi viscosity Valvoline motor oil and expect I get as much service life from the motor as I would using highest end synthetics or Quicksilver oils. Lots of valuable argument goes opposed to that, and I freely admit many people here know a lot more than I. But for the money, I believe I'm getting good service this way.
 

Lou C

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While boat engines run cooler in terms of water temp (160 vs 190 for vehicles) oil temp can be much higher due to the fact that the motor oil is circulated much faster because of high rpm use. The cooling water is circulated faster too but it's being replaced by a constant stream of cool water. The oil is the same oil potentially getting sheared down. Look at the difference between your cold idle oil pressure (40-50 psi in most cases) and your hot slow idle oil pressure after running on plane (20 in most cases), if it's lower than that, I'd say the oil may not be up to the task.
I would tell anyone do as I did and do an oil analysis, using your favorite oil. Then you will see after your typical season in your own boat, if it stays in grade. The problem with do it yourselfers is we are not engineers and we tend to go by opinion and not fact. As in, well its nothing special only a small block Chevy, why should I use that expensive NMMA motor oil? Well, you have a small block Chevy, but its not being used in automotive parameters, where the engine is rarely over 2,000 rpm for any length of time. Back in the old days one of my cousins had a '69 Chevelle SS 396 that had 4.56:1 gears. On highway trips this engine ran at between 3000-3600 rpm constantly. He used racing 20w/50 motor oil because that was the best we had back then. That is the use your boat gets, every day you use it. Wear due to inadequate oil viscosity happens gradually, then one day it becomes obvious in oil consumption, or lower than normal oil pressure readings, or wear on the cam/lifters especially in flat tappet engines.
​So after you render your opinions, post up some oil analyses so we have some real facts, not just opinions.

​Also keep in mind that the better marinizers, like Crusader, use engine oil coolers more so than Merc and Volvo. There is a reason why they are doing so...high oil temps....
 
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Lou C

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I sent a sample of Rotella 15W-40 oil from my boat engine with 55 hours on the oil to Blackstone Labs for analysis. They reported back that the TBN value was 3.8 which needs to be greater than 1.0. A search on Rotella 15W-40 oil turned up the base value was 10.1 so there was plenty of antiwear additive left. The metals content of the oil was below the average for my type of engine.

I would conclude that the Rotella 15W-40 oil is doing a good job of protecting the engine. I plan to have it tested when this oil has 75 hours on it next season to see where the TBN value is.

​I checked back to my '15 Blackstone report and the TBN on the Merc oil was 6.6. So it would be interesting to see what the SUS Vis @ 210*F and the cSt vis at 100*C was for the Rotella.
 
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