Engine Oil

dino

dino

Member
Feb 21, 2009
123
Boston MA
Boat Info
2002 380 Searay Sundancer
Engines
8.1s V-Drives
So figured I would get some opinions on changing engine oil. I change mine in the fall at the end of the season and again half way though the New England season in August. Some may say overkill I say for $150 it is worth it. I have been trying to get some info on switching to either Mercruiser synthetic blend or full synthetic from the regular 25-40 w I use now. Is it worth the money? Could I cut out that mid season oil change and just do it in the fall. Don't want to waste money on the other hand don't want to cheap out on caring for expensive engines
Hope everyone is enjoying the season
 
Seems like you might just hate money :):)

How many hours are you putting on the engines between changes? And what does your manual recommend? I assume it's non-synthetic? I'd stick with the MFG recommendation myself...and the MFG recommended interval.
 
I guess we all do if we own boats :)
I put about 75 - 100 hours on the boat a year Mecruiser manual says every 100 hours and to use the regular quicksilver 25-40w I did read that because the blend if fairly new they are recommending that as a better choice. Seems like the oil in the 8.1 gets dark and thinner halfway through the year so thought it wouldn't hurt to do the extra change
 
If it's dark and thin I'd do it. I'll change at 50 with VR-1 20 50 racing oil. $6/qt. Amazon. 15-50 Mobil 1 is good stuff and same price.
 
Switching to either the synthetic blend, or a full synthetic won’t change anything on whether you do midyear changes or not. Mercury stopped making the full synthetic oil, so if you find it, it is leftover old stock. As mentioned, changing midyear is likely overkill, but to your point, it is reasonably inexpensive compared to the rest of the cost of operating a boat.
The 8.1 motor is known for shearing oil. You want to use a very sheer stable engine oil in it. Merc oil is so so for that purpose. There are better choices.
 
I use Amsoil Synthetic oil in 100% of everything I own. It is full synthetic oil and I have had good luck with it since I started using it back in my teens. It is expensive so not for everyone but if you are looking for the best oil it is one of them.
I believe if I am going to take the time to do the oil change why not put the best oil in I can get. With a good quality full synthetic there is no reason to do a mid season oil change at 100hrs Of annual use unless you suspect contamination.
 
What you might consider doing is to start sampling your oil. That will tell you exactly what's going on with it and whether or not it makes sense to switch oil or do an early oil change. It'll cost about $20 per engine - whether it's through an online place like Blackstone Labs or find a local CAT dealer. It'll take at least 2 sample timeframes to get a good baseline, but it can be very helpful.
 
I've been a mechanic pretty much since eleven years of age working on everything from Ford 8n and Caterpillar D2 tractors to Cessna 414s and oil change intervals is always a huge topic of discussion. It seems that the one big variable that dictates the wisdom of not only spending the money but also contributing to the waste on a macro scale is regular use of the equipment. The Viscosity and lubricating properties of the oil is not compromised after even 100 hrs of normal operation. The real enemy to the internals of the engine is the caustic by-products of combustion and moisture that condenses in the block and cylinders. If the engine is used regularly and brought to operating temps each time it is run then the oil will last easily an entire season and it is a waste of resources and time to change mid season. The other thing that should be considered in over-maintaining engines is, every time service is performed by a human being, human error can be introduced.
Changing oil once a year, every year is good practice and it removes the nasty corrosive by-products of combustion and it is especially important for those of us that boat seasonally and put the boats away for a long winter layup.
A couple of hundred bucks is no big deal in the grand scheme of what we spend to own and operate these sport yachts by a long shot, but I think its just burning perfectly good money needlessly unless there is a good tangible reason otherwise. Oil analysis is a great way to get that information, especially if the engine is high time and showing some indication of wear.
Just my .02
Carpe Diem
 
Carpediem44DB said:
I've been a mechanic pretty much since eleven years of age working on everything from Ford 8n and Caterpillar D2 tractors to Cessna 414s and oil change intervals is always a huge topic of discussion. It seems that the one big variable that dictates the wisdom of not only spending the money but also contributing to the waste on a macro scale is regular use of the equipment. The Viscosity and lubricating properties of the oil is not compromised after even 100 hrs of normal operation. The real enemy to the internals of the engine is the caustic by-products of combustion and moisture that condenses in the block and cylinders. If the engine is used regularly and brought to operating temps each time it is run then the oil will last easily an entire season and it is a waste of resources and time to change mid season. The other thing that should be considered in over-maintaining engines is, every time service is performed by a human being, human error can be introduced.
Changing oil once a year, every year is good practice and it removes the nasty corrosive by-products of combustion and it is especially important for those of us that boat seasonally and put the boats away for a long winter layup.
A couple of hundred bucks is no big deal in the grand scheme of what we spend to own and operate these sport yachts by a long shot, but I think its just burning perfectly good money needlessly unless there is a good tangible reason otherwise. Oil analysis is a great way to get that information, especially if the engine is high time and showing some indication of wear.
Just my .02
Carpe Diem
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Well explained. I change oil every 100 hours or so some times it goes to 130 depending on where we are. WE put on 200+ hours a year.We have 3,300 hours on our 454s and the seem fine. Speed is as it was when we got boat at 650 hours. I have found different oils give different results. Do not remember brand but one oil I used 1/2 to 1 QT every 100 hours I switched to Shell #40 strait weight and oil consumption stopped. We run at 1,400 to 1,600 RPM most of time.
 
Im no expert, but I like Rotalla. I use it in all my other engines, including Cummings, Yanmar, Honda, Kawasaki, GM, Ford, John Deere, etc.
upload_2020-8-5_11-21-18.jpeg
 
What year is the engine? Pre roller lifters the engine needs oil with zinc and an oil formulated for diesels is zinc rich.

If it has roller lifters Mobil one is good as is most synthetics, high heat tolerance.
 
Wanderer 290 said:
What year is the engine? Pre roller lifters the engine needs oil with zinc and an oil formulated for diesels is zinc rich.

If it has roller lifters Mobil one is good as is most synthetics, high heat tolerance.
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The engines are original 2002 8.1s.....Thanks
 
Mercruiser switched to the the synthetic blend to help with rust in engines that site a-lot. . Group 4 base stocks which
are most of the standard synthetics are non-polar, meaning they don't cling to metal when not inservice. Group 3 base stocks tend to be polar and cling better. If you think about the marine engine, it gets run hard for extended times so the added load barring capability of synthetics makes sense. The extended drain interval can only be achieved using oil analysis as every motor is different, in different state of wear and can get fouled earlier than expected. As the TBN (total Base Number) changes the oil has less ability to consume the acids created during combustion. This is part of the additive package in the oil. Once it's gone the oil becomes acidic and can cause rust and corrosion. Mercuriser also has their special viscosity 25W-40. Its an all around oil they built for both 4 store outboard and inboards. The reason they do this is that the wider the range ie 15w-50, 10w 40...ect. the more viscosity builder they need. These polymers act like sponges and make the oil act thicker as it heats up. The problem is that they are shear sensitive and break down over time. So the less you need the longer they oil will stay at its design weight. So why do we need multigrade oils in boats?
Great question..... Out climate is pretty stable unless you boat in Alaska. So I use a full synthetic and change it once i hit 100 hours. I typically run 150 hours per season.
 
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Mobi; 1 has lots of Zinc

15W‐50 1200PPM Phosphorus -1300 PPM Zinc
 
Haden said:
Im no expert, but I like Rotalla. I use it in all my other engines, including Cummings, Yanmar, Honda, Kawasaki, GM, Ford, John Deere, etc.
View attachment 89699
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Except its for Diesel Engines !
Shell Rotella 4 Triple Protection® oils use a proprietary formula exclusive to Shell. They are designed to protect under the most severe engine conditions found in modern low-emission and older, hard working diesel engines
Shell Rotella T4 NG Plus 15W-40 meets the specifications for natural gas, diesel and gasoline engines, making it a true multi-vehicle engine oil.

Gasoline combustion creates different by-products than diesel. They may not be removed by the diesel engine additives. Diesel oils are designed to keep soot particle in suspension to be removed by the filter. I don't know if this could be a problem or not long term. I would use a gasoline rate oil (API) or the one above that built for both. Just my opinion. Shell Rotella is a well known proven product.
 
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