Oil recommendation 2007 Mercruiser 350 MAG

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So here is the background info:
2007 28 foot cruiser, single 350 MAG engine by Mercruiser.
Used 5 months per year, averaging 50 hours per season. 145 hours total on engine. Temperatures are 65-90 degrees F during the season.

I have used the Mercruiser 25w40 since new to avoid warranty arguements. Now that the warranty has expired, I am condering a different oil.

I have poured through this site for a few months now - thanks to all that posted. There is an amazing amount of information.

My thoughts on the oil is to choose an HDEO for the boat, based on the info I have gathered here. But I have a few questions. Shell Rotella seems to be a popular choice, and there are some good UOAs posted from it. So, would the Rotella T 15W40 or their T6 5W40 be the better choice? The dino seems to have more Z and P, closer to the Mercruiser spec, so I was leaning that way. But, as a process control engineer, I have seen raw crude at the refineries I have worked at, and the more processing to remove the waxes and impurities the better. I believe the T6 is a group 3 synthetic, so severely hydrotreated. I am ok with that as I am worried Esters in a PAO based oil would not hold up as well to contaminants and dilution (personal theory). The T6 does have a lower Vis at 100deg, lower than the Mercruiser by more than 10%. Both have a TBN much higher than the OEM, which I feel beeter about with all the sitting the boat does, low operating temps, etc.

I am posting the VOAs for the three oils so you do not need to go look them up to offere your opinions. Sorry for the long post, but the posts always say the more info provided, the better.

Mercruiser VOA
Moly Mag 1063
Calcium 422
Phos 1362
Zinc 1546
Titanium Silver Copper Lead Tin Aluminum Nickel Iron 2
Chrom Sodium Boron 196
Silicon 7
SAE/ISO Grade 2540
TBN 6.50
VIS @ 100C Cst 15.14

Rotella T 15W40
Iron 1ppm
Chromium 0ppm
Lead 0ppm
Copper 0ppm
Tin 0ppm
Aluminum 0ppm
Nickle 0ppm
Silver 0ppm
Silicon 2ppm
Boron 0ppm
Sodium 0ppm
Magnenesium 20ppm
Calcium 3322 ppm
Barium 0ppm
Phosphorous 1326ppm
Zinc 1499ppm
Molybdenum 0ppm
Titanium 0ppm
Vanadium 0ppm
Potassium 0ppm
VIS@100C 15.12cSt
Tbn 10.36

T6 5W40
Iron 2ppm
Chromium 0ppm
Lead 6ppm
Copper 0ppm
Tin 3ppm
Aluminum 1ppm
Nickle 0ppm
Silver 1ppm
Silicon 3ppm
Boron 65ppm
Sodium 4ppm
Magnenesium 1197ppm
Calcium 751 ppm
Barium 0ppm
Phosphorous 1078ppm
Zinc 1268ppm
Molybdenum 63ppm
Titanium 0ppm
Vanadium 0ppm
Potassium 0ppm
VIS@100C 13.62cSt
Tbn 11.2
 
You really do not need more than a HDEO 15w-40. They are a winner in price and protection as compared to any oils on the market. Some people use M1 15w-50 and are happy with the results.
 
I personally use rotella t6 in my volvo penta 415hp 8.2L but I think you and me both could get away with standard rotella T. I just wanted a full synthetic because I run it in the winter also, sometimes below freezing.
 
Justinf89

Did you notice a drop in oil pressure with the thinner viscosity at operating temperatures?

With the $90k investment in a boat, $$ is not the motivator in oil selection. I would pay for synthetic oil if I thought it was a better choice.
 
I went from amsoil 10w-30 to rotella 5w-40. I've noticed a significant increase in pressure. I have yet to test it in colder weather.
 
Anyone have any thoughts on the amount of viscosity improvers needed in a group 3 synthetic to make a 5w40? Would they be excessive and more prone to sheer? I think 40-50 hrs on a boat engine is equivalent to 1500-2000 miles up a big hill in your car.
 
Just a thought: Volvo Penta recommends 20w50, merc 25w40.
Just want to indicate that the high temp visc is important and that low temp visc is not, according to manufacturers. Don't go with a high spread oil like a 5w-x. No reason and a thin-out risk.
If the cooling water is not frozen it is not really "cold" in the engine compartment.
You engine probably have an oil cooler too, so It may be less sensitive to high visc than the Volvo.
I use delvac MX 15-40 in my VP 5.0Gi and it seems to work fine with good pressure.
 
Royal Purple has a nice 15W-40 Marine oil with all the right additives for corrosion resistance and anti-wear...that with a K&N filter would be my choice.
 
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Surprised Merc. wants a 25W-40 in your area. I got the 3.0LX in my 19 footer and switched to Penn. LL 15W-40. Been good so far. I was really surprised what all the T6 had in it from your VOA posting. Wow. May have to jump ship to that stuff next season. That's some good looking oil and even has moly in it, which your starting not to see much anymore.
 
any 15w-40 HDEO. change at 50hrs. its better to use dino in a boat and change more often due to moisture and fuel dilution.
 
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