What Oil should I use for '87 Mercruiser 2.5L I/O

[AxeOnDaBoat]

Hi guys new here. So its winterization time is approaching and Im looking to service my boat, meaning change fluids etc. The problem Im facing is what oil should I use for my boat? Its an 87 Mercruiser 2.5L 120HP inboard/outboard engine, has a cast iron block. GM Chevy block. The oil cap says to use 10W-30 SAE oil. Problem is Im having a hard time finding that specific oil for my engine. I was recomended to use 25W-40 full synthetic oil in it. Would that be okay? Would that cause any harm to the engine? Any additional oils that I could use that are 'better' than 25W-40? (Located in Canada Ontario if that matteres maybe for temperature wise)

 

[factorytuned2012]

10w30 has got to be easier than getting your hands on 25w40. Im no boat guy but would suggest using the manufacturers suggested 10w30. There's nearly an endless supply on Google.

https://www.google.com/search?q=10w...x2SBwYyLjExLjGgB-BG&sclient=mobile-gws-wiz-hp

 

[userfriendly]

10w30 Duron would be my pick.
40C 80
100C 12
150C 3.5
P 1,200
Zn 1,300

 

[AxeOnDaBoat]

Okay ill stick to finding 10w-30. Do you guys think outboard oil can be used in inboard engines? I found 10w-30 but it states on the bottle that it's for use in outboard engines. It's the quicksilver 4 stroke.

https://www.canadiantire.ca/en/pdp/quicksilver-4-stroke-marine-engine-oil-10w30-4-l-0281741p.html

 

[JavierH19]

Just about everyone uses 15w-40 in these. It's what I'd use.

 

[alarmguy]

^^ Personally I also would go to 15/40.

 

[AxeOnDaBoat]

Found this would this work? It says diesel on it. Would it matter if it's a T5 oil and not T4?

 

[alarmguy]

Found this would this work? It says diesel on it. Would it matter if it's a T5 oil and not T4?


View attachment 243145

It's fine, diesel will have more corrosion control. I use 15/50 diesel semi/syn in a similar engine, I wont mention it because you wont find it anywhere, well ok. Mystic 15w50. Haven't checked recently but may have a reference to a gasoline rating. I dont think I would put it in an engine calling for a 30 though and you are in a cooler climate too. I also at times use it in my motorcycle.

If it bothers you not having a gas rating than get the T4 as it carries an SN in addition to the diesel C ratings.

 

[Allaneddie]

I always went ahead and used the Quicksilver/Mercruiser 25w-40 when I had an I/O.

 

[AxeOnDaBoat]

Yeah true. Found the oil that I need the 10w-30 but it's conventional oil. Heres a picture. Not sure if it's any good.

 

[Donald]

Found this would this work? It says diesel on it. Would it matter if it's a T5 oil and not T4?


View attachment 243145

+1

 

[dadto2]

I'm pretty sure I've seen the Quicksilver/Mercruiser 25w40 at Canadian Tire. I source it from Walmart. It's a little pricier than the other choices, but I figure the $15/year extra is worth the peace of mind.

 

[Kalle.J]

I see only wrong answers.

 

[repairman54]

I ran 10-30w in my old '85 2.5 OMC for years, gave the boat away due to wood rot, engine was perfect, outdrive not so much.

 

[hemitom]

I had the same engine in one of my boats.
I ran mono grade 30 '
10w30 - 15w40 and the quick silver 25w40.
When running the engine hard the oil pressure would drop quite a bit at high rpm and idle . When hot if i pulled the dipstick the oil would run like water off of it when using 30 or 10w30.
Under the same conditions oil pressure was much better on 15w40-25w40 between the two hot pressure was about the same and the engine was quieter really a lot less mechanical noise.
Because it was cheaper and easier to get i ran 15w40 .