Engine oil question

[ShawnR]

With the variety of talents on this forum, I thought I might post this question.

I have a 1999 Indmar inboard marine engine, essentially, a Chevy 350 in a ski boat. It is seldom used, so I have not done many oil changes. The manual states a marine oil, which is not common here (in the recommended grade of 15W40). I probably did not use marine oil in the past but someone pointed out the other day that a marine engine is always under load versus a land vehicle and marine oil is slightly different in that it accounts for that. Interesting but true? Another knowledgeable person suggested using a "High detergent diesel engine oil in the proper grade of 15W40 would be better than using a 25W40 marine oil. Taking a better look at the manual, it gets away from the "marine" designation in one paragraph but states "Synthetic oil that meets our requirements of 15W40 and API SJ/CG4 is acceptable to use after 100 hours.....". Not sure if that means that non-marine oil is acceptable if using Synthetic...

Recommended " Pennzoil Marine Oil API Service SJ/CG4 15W40 or equivalent "

Readily available options
Use 25W40 Marine oil?
Use 15W40 Diesel oil (High detergent)
Use 15W40 Synthetic?

Since I am asking questions, when is detergent oil used versus non detergent oil? I could go google but answers here are always more interesting.

 

[Former Member]

I'm a fan of Synthetics, but......

Different brands can be at opposite ends of the extreme, good or bad. I can only relate to Auto applications because thats how I monitor, ie mileage, between oil changes does the mileage performance improve or decline. By viewing it over an oil change period it eliminates the fuel variations. Some cheap brands and no name brands out perform some highend recommend name brands.

Now here is a link to this exact question on a boat forum.

regular motor oil vs marine motor oil

what is the difference between the two. I always run marine oil and a friend of mine uses regular oil from auto parts stores.his motor is a mercruzer 5.0 inboard outboard. he also runs a fram oil filter from auto parts as well he says it the same as a 305 smallblock chevy .

forums.iboats.com

 

[Darren]

I'd run Shell Rotella 5w40 Synthetic. I run it in my big bore, race engine 880 Kawasaki Teryx for 13 years now, my motorcycle, and various other performance applications, and so do a lot of other people i know.

Detergent oils are used when there is a filtration system

 

[ShawnR]

Thanks @Degen

After posting, I found this which explains some of the designations well

https://www.api.org/~/media/files/certification/engine-oil-diesel/publications/mom_guide_english_2013.pdf

 

[Aliva]

I had a 140 Mercrusier inline 4 on my 20' Chaparral it was a GM marine engine. Always ran #30 engine oil never had n issue in over 12 years.
The only thing I did was avoid using gasoline with an ethanol mix, as ethanol has an affinity to absorb moisture from the air.

 

[Chip Maker]

Todays detergent motor oils are meant for roller cam engines. Any flat tappet cam engine such as 60's muscle cars (or most any pre mid eighties engine) need a high zinc non-detergent motor oil. Otherwise you can wipe a lobe off the cam quite quickly.

 

[ShawnR]

Thanks all

 

[Tom Kitta]

The way I understand this is:
detergent oil if you have oil filter as that oil carries dirt to the filter.
non detergent oil if you do not have oil filter - you do not want dirt to be in oil if nothing is filtering it out.

 

[ShawnR]

I ended up with Rotella 15W40 as the specs were met and recommendations as above and from others.

Thanks all.