What Motor Oil??????

Dmaxx85

Petty Officer 2nd Class
Joined
Jun 16, 2011
Messages
117
Hello there I'm sure this question has been asked and answered before but I want to ask for myself.
I'm very curious as to what everyone is running for a motor oil in their Mercruiser's???? About to change the oil in my 98 4.3 merc and would like to hear what everyone is running and what they recommend!? Also I do hear of guys running 15w40 oil for diesel motors? Curious about this also! And does anyone recommend running synthetic motor oil????
Thanks for you time!
 

Silly Seville

Senior Chief Petty Officer
Joined
Dec 5, 2009
Messages
798
Re: What Motor Oil??????

Hello there I'm sure this question has been asked and answered before but I want to ask for myself.
I'm very curious as to what everyone is running for a motor oil in their Mercruiser's???? About to change the oil in my 98 4.3 merc and would like to hear what everyone is running and what they recommend!? Also I do hear of guys running 15w40 oil for diesel motors? Curious about this also! And does anyone recommend running synthetic motor oil????
Thanks for you time!

Please, pretty please...just do a search for "oil" with the provided search function. There are thousands of opinions already given on this subject...seriously! :facepalm:
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Re: What Motor Oil??????

Hello there I'm sure this question has been asked and answered before but I want to ask for myself.
I'm very curious as to what everyone is running for a motor oil in their Mercruiser's???? About to change the oil in my 98 4.3 merc and would like to hear what everyone is running and what they recommend!? Also I do hear of guys running 15w40 oil for diesel motors? Curious about this also! And does anyone recommend running synthetic motor oil????
Thanks for you time!

Ayuh,..... Yes,......

I maintain a fleet of barges, that all get 15W-40 Rotella T motor oil,...
My personal barge, with a 4.3LX gets Mobil 1, 15W-50,....
 

Starcraft5834

Lieutenant Commander
Joined
Jun 2, 2013
Messages
1,677
Re: What Motor Oil??????

DM I went to walmart and bought 20-40.. it works just fine.. if you feel better buying synthetic, go for it.. not necessary.. MHO
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,583
Re: What Motor Oil??????

Engines stopped failing many years ago from oil. They all fail due to manufactures defect and lack of maintenance, lack of maintenance is number one. What ever you use, changing it regularly
 

Lager

Petty Officer 2nd Class
Joined
Jan 19, 2014
Messages
120
Re: What Motor Oil??????

Diesel motor oil uses a molecular base very similar to synthetic oils plus it has an additional amount of additives like anti wear, anti foaming, extreme pressure and increased detergents (sludge depressants) and it cost less then synthetic IF cost is an issue for you.
Diesel oil is formulated to survive in increased pressures and mileage their engines are required of. Its fine for a boat but not so good for car or truck engines that have cat converters because its high sulfur content that will harm the catalyst.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Re: What Motor Oil??????

You have many good choices....and a few to avoid....what I'd NOT use is any automotive based 5w/30, 10w/30 or 10w/40...
here are some good ones...
Merc 25/40, straight 30 or 40, or 20w/50, or the 15/w/40 that is both gas and diesel certified.
 

agallant80

Commander
Joined
Oct 25, 2010
Messages
2,328
Re: What Motor Oil??????

Engines stopped failing many years ago from oil. They all fail due to manufactures defect and lack of maintenance, lack of maintenance is number one. What ever you use, changing it regularly

Yup. I have never heard of a motor blowing up from the wrong oil.
 

Lager

Petty Officer 2nd Class
Joined
Jan 19, 2014
Messages
120
Re: What Motor Oil??????

yeah, me neither, but i still pay the extra $ for the good stuff.
Still cant figure out why member Lou C says we cant use automotive based oil like a good quality 10W-40 ?
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: What Motor Oil??????

On my Sunrunner I didn't use anything special because we only got about 15 hours a season. I kind of used Bondo's grease rule for oil.
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
Re: What Motor Oil??????

Car oil is not formulated correctly for the work a boat engine has to withstand. I'm sure you don't drive you car around at WOT all through town like you do your boat on the lake. If you do I'm sure your car is a pile and you no longer have a drivers license. :heh:

Stick with the quicksilver oil.
 
Last edited:

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Re: What Motor Oil??????

Because its going to shear down in use and then you will be posting "after my boat came off plane the oil pressure gauge read 5 psi, why is that happening"
Car engines don't run at 3500-4000 rpms in normal use right? Well marine inboards do. So car based oil is inadequate. NOT one engine marinizer recommended car based oils. They all recommend something you would not be using in a car. Its good to question things sometimes but don't think you can out smart engineers. They specify what they do for a reason. Yeah, yeah I heard all the conspiracy theories about Merc and their special oil. Well the car companies do the same thing. Chrysler with their ATF+4 which was not in the aftermarket for a long time, the Japanese cars that all use some proprietary auto trans fluid, etc. I use what they say and guess what I have had minimal problems over the years.
 

WIMUSKY

Moderator
Staff member
Joined
Sep 26, 2009
Messages
19,790
Re: What Motor Oil??????

Gee, after reading some of these posts, I feel lucky my I/O didn't blow during all the years I owned it using 10w-40 motor oil......
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
Re: What Motor Oil??????

Gee, after reading some of these posts, I feel lucky my I/O didn't blow during all the years I owned it using 10w-40 motor oil......
Same here, especially with the 1983 120hp Merc I had. I would run that at WOT or close a lot with the same oil I put in my trucks.
 

Lager

Petty Officer 2nd Class
Joined
Jan 19, 2014
Messages
120
Re: What Motor Oil??????

Well this has been interesting.
Ive found two separate groups.
One uses only the best, recommended by the engine manufacturer and refuses to deviate because they think engine life will suffer.
The other group uses common oil and found it to work well also.
Think its interesting that no one has said anything about their engine life being degraded by using a cheaper oil and proved it by an oil diagnosis showing a loss of viscosity improvers or additive chem degradation due to marine loads or usage.:dejection:
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: What Motor Oil??????

Well this has been interesting.
Ive found two separate groups.
One uses only the best, recommended by the engine manufacturer and refuses to deviate because they think engine life will suffer.
The other group uses common oil and found it to work well also.
Think its interesting that no one has said anything about their engine life being degraded by using a cheaper oil and proved it by an oil diagnosis showing a loss of viscosity improvers or additive chem degradation due to marine loads or usage.:dejection:

There's a third "group".

You can use what I use.


It's in my "sig" (below)..............


Cheers,


Rick
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Re: What Motor Oil??????

That's because most people on these forums are not professional mechanics, do not take old engines apart, analyze wear patterns and failure modes. An engine can run fine while experiencing higher than typical levels of wear. The typical boat owner uses his engine maybe 50 hrs per year. Of course problems are going to take years to show up....
iI you have an oil pressure gauge, it will tell you that multi-vis car based oils thin out when run at 4000 rpms for extended time periods. You buy a $55K diesel truck and you use Chevron Delo, Rotella T or other diesel oil right? If people went on the diesel truck forums and continued to stubbornly insist that they know more than engineers they would be laughed off the forums. So with this its the same thing...
 
Top