15W-40 Royal Purple Synthetic diesel oil question.

[SJ30]

I have decided to service my boat myself. The previous owner said he used the 15W-40 Royal Purple Synthetic oil. The only Royal Purple 15W-40 I can find says it is for diesels. Should I stay with the Royal Purple or change to another brand?

[jmo]

Many 15w-40 weight oils target the diesel truck segment but many are compatible with both diesel and conventional engines - just make sure the oil has the proper SAE certification on it that your engine calls for - "SN" is the most recent. In regards to synthetic oil, I personally think it's waste of $$ as we all change the oil at the end of the season anyways, so it's never going to allow you to extend the interval period - which Nautique does not recommend anyways even if you are fortunate enough to live somewhere where you can go year round.

Of interest, the info on the 15w-40 RP says it has the zinc additives needed by flat tapper motors - but given you have an 2008 I highly doubt that is applicable for your engine.

I personally now run Shell Rotella 15w-40 conventional oil in my Excalibur engine, which is also labeled on the front for Diesel engines but can be used in gas engines as well.

[swatguy]

Not to start an oil war, but I echo everything said above. Shell Rotella in all my boat engines. Two of those engines went well past 1300 hrs with nothing but fluids and general maintainence. I know the new owners of those boats went well beyond that as well.

If you're more comfortable running the Syn by all means go head.

[vvfdfirefighter]

IMO Shell Rotella is about the best oil you can ever use. I run it in everything; Truck, Boat, ATV, Tractor etc. Sadly my engine in my truck had an internal failure last year. When I dug into the motor it was obvious a rocker retaining clip had broke; sending the rocker all over in the valve cover. To my surprise, after tearing the motor all the way down, it was very, very clean inside. The shop that re-worked my engine even asked me what oil I ran in it because it was the cleanest engine they've seen.

Shell Rotella uses actual cleaning agents and real lubes.

[nyryan2001]

So Indmar did a test a few years back.

350s start to burn/ destroy oil just over the 40hr mark.

I don't have the test.... Guys over in the MalibuCrew have it, but I've seen it.

No conjecture... Fact.

So I wouldn't say synthetic is a waste of money. If you run regular oil... Change it every 40-45hrs.

[Nautiquehunter]

Rotella was preferred because of its high ZDDP content its my understanding they has cut the level back on today's product. ZDDP is required on older flat tappet engines today's engines are all roller lifter . I use Mobil 1 in all my engines. The boats use 15w50 witch have all the additive required for both older and newer engines. The 15W50 is the only weight that has all the additives. If you are going to use any other brand or weight I suggest you contact the manufacture for their recommendation.

[SJ30]

Guys, thanks of your input. It is good to hear from folks with more experience than me.

[swc5150]

I don't want to start an oil war either, as everyone is entitled to whatever they want to use. However, PM Jody Seal or search some of his threads here if you're interested in his proven engine performance increases using RP in his 200's. If you're ever going to trust anyone when it comes to PCM engines, it would be Jody.

[jmo]

I don't want to start an oil war either, as everyone is entitled to whatever they want to use. However, PM Jody Seal or search some of his threads here if you're interested in his proven engine performance increases using RP in his 200's. If you're ever going to trust anyone when it comes to PCM engines, it would be Jody.

It would be cool to see this data - maybe we need an official oil sticky thread given these questions come up so frequently...

[doxalubes]

I have decided to service my boat myself. The previous owner said he used the 15W-40 Royal Purple Synthetic oil. The only Royal Purple 15W-40 I can find says it is for diesels. Should I stay with the Royal Purple or change to another brand?

It's great to hear that you've decided to service your boat yourself. Regarding the oil, the Royal Purple 15W-40 Synthetic oil used by the previous owner is a high-quality product, even if it is labeled for diesels. Diesel oils typically contain higher levels of detergents and anti-wear additives, which can be beneficial for many engines, including those in boats.

Sticking with Royal Purple can be a good choice if you’ve been satisfied with its performance. However, if you’re considering switching, there are other excellent options available. Fully synthetic 15W-40 diesel oils are designed to offer superior protection and performance, particularly in demanding conditions. Brands like Shell Rotella, Mobil 1, and Castrol all offer fully synthetic 15W-40 diesel oils that are highly regarded.

Fully synthetic oils provide better protection against wear, higher resistance to thermal breakdown, and improved performance in extreme temperatures, making them suitable for both diesel and some gasoline engines. Just ensure that any oil you choose meets the specifications and requirements of your boat’s engine.

Ultimately, whether you stick with Royal Purple or switch to another brand, the key is to use a high-quality, fully synthetic 15W-40 diesel oil to keep your engine running smoothly and efficiently.

Hope this helps, and happy boating!