Preferred engine oil?

[Scotto97]

I'd like to ask members what oil they typically use in their Mercruiser engines

Synthetic?

Mercruiser 25-40?

Another brand, grade?

Thanks

 

[skolbe]

What it says in the manual Synthetic Blend - Merc oil.

 

[Southpaw II]

Mercruiser 25-40

 

[tdappleman]

I was using the Mercruiser 25w40 and Merc filters and switched to Amsoil 10w40 Marine oil in the spring. Motors are running great - oil pressure is up slightly and more consistent across both motors. An interesting thing is the oil is a lot cleaner than when I ran the Merc oil. I have about 55 hours on this oil and it's a dark amber but not almost black like previously. I'm also using Amsoil Ea filters which may be helping me as well. If you are still under warranty I'd only use the Merc blend - out of warranty use the oil you like which is TC-W rated.

 

[northern]

We have twin 454s and use SAE 40. In the owners manual it provided several options based on temperature and 40 works for us. Change oil every 250 hours that is usually once a season. Used to change it every 100 hours until other people told me they ran 250 hours between changes. We use 10-30 in the quicksilver 8KW generator. Change this oil every time I change the main engine oil that is about 100 hours of generator run time.

 

[BarryCF]

250 hour between changes? You're killing your engine this way. Thats the equivalent of approximately 10K miles in a car. A car that is not even close to the engine load of a boat. There is a reason for the factory reccomended interval...

And it's not that they are partnered with "big oil".

 

[BahamasBlair]

I use nothing but Merc 25W40 Synthetic blend. It gets changed every 100 hours religously. I have 450 hours on my 8.1s and they run better than new.
Don't try to save bucks on oil - it's not worth it.

I can't confirm the validity of Merc's claim, but they say on their website that the inboard version of their 25W40 has extra rust protection added to the blend. It's a bit more expensive but what the heck.....
Enjoy the boat.

 

[PMC]

I use nothing but Merc 25W40 Synthetic blend. It gets changed every 100 hours religously.

+1:thumbsup:

Don't try to save bucks on oil - it's not worth it.

+1000:thumbsup::thumbsup::thumbsup:

Oil is not an expensive maintenance cost. I have no problem spending a few extra bucks on this.
My approach as a DIY kind of guy, is spend the most on materials. Work with the best, and still come out ahead saving on labor.

 

[300 Ray]

I have an '86 300 with twin 350IB's I use Pennz HD 15w40 with one quart of synthetic. I might be weird but have always had good luck with this. Change every fall no matter what hours i turn.(never 250 though) More like 60 - 70 here in upstate NY where it rains every weekend! LOL. Gen gets 30w synthetic.

 

[Alex D]

I run Castrol GTX High Mileage 20W-50 in my engines and Chevron DELO 400 15W-40 HDEO in the genny.
The Castrol HM is an extremely good engine oil. One of my slip neighbors ran regular GTX 20W-50 in his Skater cat with twin 1050 hp Mercruiser supercharged 502 cid race engines (that boat ran 140 mph on our lake ... clocked by radar). GTX HM has an extra stout additive package for wear protection and is as loaded and break down resistant as marine oils. I also change my oil twice a year so about every 30 hours since we only put about 60 hours a year on the boat.

BTW you can look up oil analysis of the Merc 25-40 oil on www.bobistheoilguy.com forums. It has no secret, special additive package and is quite avarage from that perspective. Only thing special with the Merc oil is that it contains no viscosity improvers like most multi viscosity oils. It is simply a mix of low and higher viscosity oils. Viscosity improvers are prone to breakdown over time and especially in high rpm/load situations which then leads to sludge. SLudge in many ways are the broken down viscosity improvers of overstressed oil.

 

[fc3]

Correct URL http://www.bobistheoilguy.com/

 

[JOHN R.316]

I only use Amsoil
Synthetic Heavy-Duty Diesel & Marine Motor Oil SAE 15W-40 (AME)

 

[glenn5]

have 1988 merc 350 blue water inboards and run 20w-50 Valvoline synthetic. previuos owner ran a 15w-50 Mobil synthetic. I couldn't seem to find the mobil 15w-50, so that is why I switched to 20w-50 valvoline synthetic. no problems yet

later

 

[sr330daguy]

Straight SAE 40 ,never a problem,I'm not a fan of muli viscosity oils in an engine that is always under load.

 

[Theresamarie11]

Straight SAE 40 ,never a problem,I'm not a fan of muli viscosity oils in an engine that is always under load.

Here in the northeast, our mechanic says the same but they only use straight SAE 30 (doesn't get all that hot here).


Terri