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ALF1

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I have a simple question to ask. What is the benifit of using marine engine oil over regular car engine oil for my 5.7 Mercruiser engine?
 
My opinion - not a lot to speak of. A good HD multi-viscosity auto motor oil worked fine in my Crusader's over may years. Just change the oil and filter IAW the maintenance schedule. In my current Honda 225 outboard, I use Penzoil 10W-30. Oil is changed every 100 hours.

However, I'm certain others will disagree because of the unique marine environment. A good discussion can be found at
http://blog.boattrader.com/2012/07/marine-engine-oil-avoiding-viscosity-breakdown.html
 
ALF1 said:
I have a simple question to ask. What is the benifit of using marine engine oil over regular car engine oil for my 5.7 Mercruiser engine?
Click to expand...
because it is tested to ensure quality, but even Mercruiser says you can use automotive oil, but it's their "5th best" option in the manuals.

http://www.mercurymarine.com/serviceandwarranty/mercruiserfaqs/fueloil.php
What type of oil should I use? Can I use synthetic oil?

Engine Oil

To help obtain optimum engine performance and to provide maximum protection, we strongly recommend the use of the following oils listed in the order of recommendation:

1. MerCruiser / Quicksilver Synthetic Blend, NMMA FC-W rated, 4 cycle oil.
2. MerCruiser / Quicksilver 25W40 NMMA FC-W rated oil.
3. A NMMA FC-W rated oil.
4. MerCruiser / Quicksilver 4-cycle 25W40, non FC-W rated oil.
5. A good grade straight weight detergent automotive oil per the operating chart below.
faqs_temp.gif


NOTE: The use of non-detergent oils, multi-viscosity oils (other than as specified), non-FC-W rated synthetic oils, low quality oils or oils that contain solid additives are specifically not recommended.

http://www.nmma.org/certification/programs/oils/registeredoil.asp?y=FC-W2008
 
hYSTA, THANKS FOR THE POSTING OF THE RECOMENDED OIL VELOCITY. i AM SHOCKED AT THE NUMBER OF FOLKS WHO NEVER READ THEIR MANUALS OR USE WHAT i CALL cAR GRADE multi oils. 5-30 10-30/40 or the like.
Running a boat on water is like drive a car constantly up a mountain. My first new boat in 93 I changed the oil after the 10 hr break in. Out skiing on Lake Erie in the Sandusky Bay I noticed my oil pressure drop when I would loose a skiier, drop the throttle and turn back. Turns out it was the multi grade oil in the baor from the oil change. Since I use 40 weight Wolf's Head. Best ever, cheaper and has more anti foaming agents.
Mercruiser said "NEVER use multi Grade oil. Use it on all of my boats.
Gator
 
Automotive grade oil has additives in it to keep it from breaking down during normal use. This is how they can take a low grade oil and make it usable in cars.

Your boats engine does not see normal use, it sees severe use. During severe use the additives in Automotive grade oil break down allowing the oil to break down.

Quick Silver 25/w40 marine engine oil, does not have any additives in it, hence it does not break down.

Now people will argue with me on this, But, is it really worth the $10 you will save on Cheaper Automotive grade oil?

I use QS 25/40 in my Cummins. Engine is clean as a whistle inside.
 
Well folks, this is probably about the tenth thread on marine oil that I have participated in over the last several years. As I posted earlier, there are many different perspectives. In this case, we are talking about a marine inboard engine. I'll stick to my original post -a good HD multi-viscosity auto motor oil will typically work fine - just change the oil and filter IAW the maintenance schedule. An outboard generally works harder than an inboard in terms of rpm's, operating ranges, and stress. So in my Honda 225 I use Pennzoil 10W-30 with an API certification of SG or higher, as recommended by Honda. I also religiously change the oil at the recommended every 100 hours. For me, that means about three oil changes every year.

The more important issues include (1) making sure your engine gets up to a sustained operating temperatures at each usage and to keep the engine decarbonized as much as possible. That includes using fuels that are pre-treated with a decarbonizer like Valvtect Carbon Free, or adding a decarbonizer at regular intervals like SeaFoam or YamaLube Ring Free, or similar; (2) using clean fresh fuel; and (3) using an inline fuel-water seperator, which should be drained every 100 hours and changed every 400 hours. Also, thermostats should be checked on a regular basis. The easiest way to do that is to install temperature gauges which will allow you to constantly monitor operating temperatures. When t-stats fail, they most often fail in the open position. That will keep your engine running too cool, and will allow water condensation to mix with your oil, greatly depreciating its effectiveness.
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