Best Oil for John Deere?

[TrawlerDavid]

I have a 1976 GB 36 with twin John Deere 6404 diesel engines. The engine manual specifies SAE 30 oil. The mechanic who did the oil change when I purchased the boat used DELO 15-40 and recommended it as superior to the SAE 30 for the John Deere engines. Any concerns about not following the manual specs for SAE 30 and using DELO 15-40 instead?

 

[rslifkin]

Outside of an old Detroit 2 stroke that has specific oil requirements, I personally wouldn't use a straight weight oil in anything without good reason at this point. Modern multi-viscosity oils aren't even close to the poor performing, shear-prone ones that the manufacturers were shying away from 50 years ago.

I can't think of a good reason why a good quality 15W-40 wouldn't be a suitable oil for those engines. A 10W-30 HDEO would also likely be fine, as the engines were originally expected to run on a 30 weight oil.

 

[TrawlerDavid]

Outside of an old Detroit 2 stroke that has specific oil requirements, I personally wouldn't use a straight weight oil in anything without good reason at this point. Modern multi-viscosity oils aren't even close to the poor performing, shear-prone ones that the manufacturers were shying away from 50 years ago.

I can't think of a good reason why a good quality 15W-40 wouldn't be a suitable oil for those engines. A 10W-30 HDEO would also likely be fine, as the engines were originally expected to run on a 30 weight oil.

Thanks! That was pretty much my conclusion and appreciate the shared wisdom. I was a sailor for 50 years and am finding I am very much enjoying the new adventures with the GB 36.

 

[High Wire]

Where do you keep the boat? Ambient air temperature for startups matters.

 

[tiltrider1]

I am sure he used Delo 400 15-40. Delo 100 15-40 is formulated for 2 stroke diesels such as the old DD-671, where Delo 400 is formulated for 4 stroke engines.

 

[TrawlerDavid]

Where do you keep the boat? Ambient air temperature for startups matters.

In Seattle on the Sound. Temps spring through summer when we use the boat are rarely below 32 degrees. I had a Pearson 33 on the Bohemia River from 2014-2023 when we liven in Philadelphia, and after a lifetime on the West coast it was an education to have have to pull the boat every winter.

 

[Comodave]

I run 14-40 Rotella. Never had any issuwith it. The laot boat we had speced 30 weight oil but the PO had been running 14-40 for over 15 years so I stuck with it.

 

[Crux]

Check JD Service Bulletins.....just call a JD service dept and they'll email it....
I would trust their authority above all others

 

[mvweebles]

@rslifkin is spot on. The modern multi-vis oils are far superior to the old school single weights. A good friend worked at Deere Marine for a while before joining Alaska Diesel 20 years ago. I forget the grade certifications but as long as they are on the label, you're good (all reputable diesel rated oils meet the requirements). I run Rotella T-5 in my ancient Perkins 4.236. You could run T-4 if you want to go old school pure dinosaur blend. Honestly, your engine won't care even if you run a slightly offbeat oil - something else will kill it long before an oil grade related issue (within reason).

Don't overthink this.

Peter

 

[TrawlerDavid]

@rslifkin is spot on. The modern multi-vis oils are far superior to the old school single weights. A good friend worked at Deere Marine for a while before joining Alaska Diesel 20 years ago. I forget the grade certifications but as long as they are on the label, you're good (all reputable diesel rated oils meet the requirements). I run Rotella T-5 in my ancient Perkins 4.236. You could run T-4 if you want to go old school pure dinosaur blend. Honestly, your engine won't care even if you run a slightly offbeat oil - something else will kill it long before an oil grade related issue (within reason).

Don't overthink this.

Peter

Thanks, Peter. Sound advice. My JD 6404's only have about 2500 hours on them, and have had consistent maintenance by the prior owners, so I'm hoping that with continuing and conscientious care they will be good for another 2500 before I need to worry about anything serious. They'll likely outlast me.