I don’t really understand the alphanumeric specification system of motor oils. The manual on my engine calls for 15W-40 SJ/CG-4 (or better). The only oil I could find that was similar is labeled “CJ-4 Plus”.
Can anyone tell me: a) what this means, or b) if it’s safe for my engine?
If it matters, the engine is an Indmar 5.7L
I guess each new specification is an improvement. I think the CJ-4 is just a newer specification than the CG-4. My old truck calls for SE 10W-30. I am running SM 0W-30 synthetic in it.
the “SJ” part means its API certified for spark ignition (i.e. gasoline) engines. the “CG” part means it is certified for compression ignition (i.e. diesel) engines. if your engine requires an SJ certified oil then one with only a CG rating shouldn’t be used. many oils can and are certified for both S and C.
I would be stunned if that marine engine didn’t call for synthetic, which would surpass all ratings, etc.
Oh… nice engine! I’m getting my 8.2 liter Mercruiser rebuilt… and in the process, I’ve discovered much love for Indmar marine engines.
ETA: No debates about synthetic vs. conventional oil, please! My comment is about the typical advice in the marine world, which is almost always synthetic.
Yes, I am only a recent convert to synthetic. I am getting beat up for it on an auto forum. Somebody there made the informative, factual post ‘‘Mobil 1 sucks’’. I enjoy not seeing that sort of thing here.
This may mean I need to drain and refill with a CG certified oil. I’m still unsure what “CJ” refers to. (I changed the oil already, but haven’t started the engine.)
S, like in SJ, means “spark”- gas engine. C, like in CJ, means “compression”- diesel engine. The second letter is a quality letter that changes when the oil is improved: SJ is better than SH, CJ is better than CH, and so on. I think it’s up to SN on some brands now. For example, it’s fine to use SN oil if SH is called for, but not to use SH if SN is called for. Same with the C ratings.
Motor oil/additive packages are tweaked frequently for any number of reasons, more recently some of the changes are to modify or reduce additives that have a negative impact on modern emissions control systems; not sure how much of that is applicable to a marine engine.
but as california jobcase said, it’s fine to use a newer revision of oil than your engine calls for, but you really want to make sure it has the right certifications. the problem you’re running into is that 15W40 is a common viscosity for older diesel engines, but not so common for gas engines. The older oils I used in my diesel trucks were dual rated for gas and diesel engines (back then the standards were SF/CD.) but with the complexity of modern diesel emissions controls, I think that there are more commonly separate oils with no S* rating but only a C* rating.
you might have to track down a “marine” motor oil to get what you need, and pay through the nose for it.
I dug out the container. Here’s the actual wording on the back:
“Compatible with API Service classifications:CJ-4, CI-4 PLUS, CI-4, CH-4, CG-4, CF/SM” (bolding mine).
Is the SM referring to a Spark-ignition classification? Or something else? I’m assuming SM is a couple of steps up from SJ.
BTW: Thanks everyone for your help.
yes. you should be good to go.
it’s “newer,” not necessarily “better” unless your engine requires the newer standard.
No the oil you found is the wrong oil for your engine.
When dealing with API certifications S means a spark engine, according to your link this is what you have.
C on the other hand refers to a compression ignition engine.
Assuming the certification on the bottle is only CJ-4 plus, it is not certified for gas engine use. While it might work, it is not certified for that use.
In general, the later certifications are just fine for use in older engines. However there is one huge exception, new oils have lower levels of Zinc and Phosphorus in the additive package. This is to prolong the life of the catalytic converters on modern cars. Unfortunately, there are some old classic car engines with flat tappets that require this in the oil or the camshafts will be damaged in short order Owners of these vehicles are running either either Diesel engine oil or adding an additive called ZDDP to prevent damage to their classics.
Google ZDDP for more info about this.
Oh and just so you know, Mobil 1 doesn’t suck. Might not be the best oil out there, but it doesn’t suck. 
ETA: Go here and click on “Engine oil guide” for a complete rundown on engine oils
Rick, he said it’s labeled “CF/SM.”
Didn’t the specs say roller tappets?
Missed that in the second post. OK, the oil is fine for that engine. SM is just fine as a replacement for SJ. It is only when replacing SC, or SD oil that issues occur.
And yes the engine has roller tappets according to the specs.