What oil should I use?

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DanOnTheBoat

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So... looking to change my boat engine oil this year before winterizing it. What oil should I use? I have a 4 cylinder 2.5, 120hp merc inboard/outboard engine. Its an 87. It has an oil cap on it saying 10W-30. I looked online to see what comes up, I found few online a Quicksilver to be specific its a 10W-30 the thing is it says that its for us in 4-cycle outboard engines. Would I be able to use that in my engine? It seems like all of these oils say outboard and none for inboard. Although, there is a 25W-40 oil that is for us in outboards and inboard engines(still Quicksilver) Would there be a problem if I use that oil in my engine? Where would i buy my oil from to make sure its compatible with my I/O?(Canada) Also I heard that full synthetic isnt really good for cast iron blocks, is that true?
 
Bondo

Bondo

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Ayuh,..... I run Rotella 15W-40 in everything I've got,.....
You can run any oil you'd like,..... just don't over-think it,.....
 
Lou C

Lou C

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Just not an automotive 5/30 that will thin out with sustained high rpm use. 15/40 or 20/50 are good and much cheaper than the marine oils.
 
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DanOnTheBoat

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Sounds good Ill go with the 25W-40 that I found online. Rated for inboards and outboards.

Would any harm be done if I run regular full synthetic car oil in my inboard? Or are they different oils?
 
JASinIL2006

JASinIL2006

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Full synthetic will be fine. I run it in my boat engine. Honestly, any oil will be fine as long as you use the right viscosity and change it after every season.
 
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paulswagelock

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Keep it simple. Run Delvac, Delo or Rotella 15w40 in it. if you want, use their semi synthetic blend versions but not even necessary. These 3 are available everywhere and inexpensive.
 
Bondo

Bondo

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DanOnTheBoat said:
Rotella makes marine oils? Or are all of those brands for cars? Found Rotella 15w-40 T5 oil. Would that work for a 87 I/O 120hp merc motor?
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Ayuh,...... As it says right on yer oil cap,...... Engine oil,....
Rotella makes fantastic Engine oils,.... it'll work perfectly for yer motor,.....
 
Lou C

Lou C

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that label is a GM label for an automotive application no doubt
Merc never recommended an oil of that viscosity in their inboards (they recommended straight 30, 40, 20/40, 20/50 or their 25/40).
if you don't want to use high priced "marine" oils another option is
Valvoline VR-1 20/50, this probably has even more zinc than Rotella or Delo, by a large margin. Also cheaper than the "marine" oils as well.
 
Scott06

Scott06

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DanOnTheBoat said:
Rotella makes marine oils? Or are all of those brands for cars? Found Rotella 15w-40 T5 oil. Would that work for a 87 I/O 120hp merc motor?

Found this:

View attachment 401979
Click to expand...
Use the T4 conventional rotella . It has enough zinc for flat tapped cams And is an excellent value
 
Scott Danforth

Scott Danforth

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dont overthink it. you need zinc in the flat tappet motor you have.

as stated. get the rotella T4 15w-40 diesel motor oil.
 
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airshot

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Very very few engine issues are oil related, most are from lack of or improper maintenence !!
 
jimmbo

jimmbo

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DanOnTheBoat said:
So... looking to change my boat engine oil this year before winterizing it. What oil should I use? I have a 4 cylinder 2.5, 120hp merc inboard/outboard engine. Its an 87. It has an oil cap on it saying 10W-30. I looked online to see what comes up, I found few online a Quicksilver to be specific its a 10W-30 the thing is it says that its for us in 4-cycle outboard engines.Would I be able to use that in my engine? It seems like all of these oils say o utboard and none for inboard. Although, there is a 25W-40 oil that is for us in outboards and inboard engines(still Quicksilver) Would there be a problem if I use that oil in my engine? Where would i buy my oil from to make sure its compatible with my I/O?(Canada) Also I heard that full synthetic isnt really good for cast iron blocks, is that true?
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Mercury/Quicksilver offer more than one 10-30 Oil, some are labelled for Outboards, some aren't. The Engine Manufacturers know their Engines and what they require to avoid a Horrible Twitching Death. I know there are some here that will insist that there is No Difference between a Auto/Truck Engine and a Marine Engine... Well a Marine Engine works-runs under an entirely difference set of Parameters, and thereby subject to different Demands, and that can place different demands on Lubricants, and might need a different Formulation/Additive Package more suited to the Marine Operational Environment. But to some Oil is Oil...
 
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KJM

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I would just use whats called for on the cap. 10w30 regular engine oil.
 
Lou C

Lou C

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That’s there because the oil cap is put there by GM for automotive applications but that’s not good for marine use running at 3500-4000 rpm all day….
Merc says 25/40 and you can use 15/40 or 20/50.
 
Scott06

Scott06

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Lou C said:
That’s there because the oil cap is put there by GM for automotive applications but that’s not good for marine use running at 3500-4000 rpm all day….
Merc says 25/40 and you can use 15/40 or 20/50.
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Exactly my similar vintage 3.0 had same cap on valve cover but merc documentation recommended straight 30 w or 40 w depending on ambient temps
 
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crazy charlie

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JASinIL2006 said:
Full synthetic will be fine. I run it in my boat engine. Honestly, any oil will be fine as long as you use the right viscosity and change it after every season.
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WRONG!!! WRONG!!! DONT DO IT!! Switching from a conventional oil to a synthetic in an older motor will result in oil leaks.Everywhere that your engine seals have benefitted from the additives in conventional oil to keep your seals plumped up will result in an oil leak.Synthetic oil does not have the same qualities as conventional oil to keep the seals from seeping and leaking.NEVER EVER switch to synthetic oil in a motor that has had conventional oil in it for a number of years.NEVER. Been there....done that.... and will never do it again.No need to dispute this.Charlie
 
jimmbo

jimmbo

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crazy charlie said:
WRONG!!! WRONG!!! DONT DO IT!! Switching from a conventional oil to a synthetic in an older motor will result in oil leaks.Everywhere that your engine seals have benefitted from the additives in conventional oil to keep your seals plumped up will result in an oil leak.Synthetic oil does not have the same qualities as conventional oil to keep the seals from seeping and leaking.NEVER EVER switch to synthetic oil in a motor that has had conventional oil in it for a number of years.NEVER. Been there....done that.... and will never do it again.No need to dispute this.Charlie
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Poppycock. I switched, from Dino Oil to Synthetic on an Engine with 110,000 miles on it, and it didn't leak, or burn it any faster. It now has over 250,000 miles on it and still No Difference.
 
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