Inboard Boat Oil

[Coach]

I have an boat with a mid engine 350 in it(about 300 hp). The last owner was using Delo 400 15 - 40 motor oil. I have always used a straight 30 weight in all my 4 cycle boat motors.
Any thoughts on staying with the Delo 400?
If I posted this in the wrong section please let me know. Thanks in advance
Coach

 

[BOBISTHEOILGUY]

you did good on picking the section, thanks.

As for what oil to use, Many/ most of my boaters use the straight 40wt down here in florida. The delo 15w40 will work fine as well. One thing to keep in mind is make sure you do proper consistant oil changes as the temp on an inboard engine can get pretty extreme sometimes due to lack of air flow. With some of the more higher grade oils such as mobil/amsoil and schaeffers, that's not near a problem.

The reason why most use straight weight oils was the problems with is the shear stability of the VI improvers that is with multivisocity oils such as the 15w40. Awhile back that would have been a big problem but with the newer oils today, the 15w40 is fine. Myself, I like the straight 40wt no reason particular but down here in florida, it's a good enough oil to hold up under the extreme temps it sees in the summer as well the fact there's only two speeds in most boat, stop and wide open.

 

[joee12]

Coach, welcome to the site. Have you considered running an analysis on the Delo that is currently in the engine to see how it is doing? -Joe

 

[Coach]

Bob, thanks for the advice. I'll give the Delo 400 a try.
As far as an analysis on the oil, I had not given it any thought. How would I go about getting that done?

 

[Drstressor]

That's good advice, Bob. Boat engines operate under the most severe conditions possible. Sort of a mix between the Indy 500 and a sled pull. Then there is the issue of standing idle in a humid environment for long periods of time. High viscosity HD oils are the way to go.

My question is: How do the additive packages compare between HD 15W-40 oils and straight weight 40? I assume you recommend a CH/I-4 diesel 40, right?

 

[joee12]

Coach, give Blackstone Labs a call at (260) 744-2380 and order a kit. One you get the kit, you put oil into the sample bottle and ship off to Blackstone. Do you have to siphon the oil, or do you have the drain tube?? Joe

 

[ghost]

I have a 1987 with twin 350 GM engines. I use straight 40wt in the engine that is orginal to maintain oil pressure at idle, but I use 15/40 Shell Rotella in the other engine that is a rebuilt and has a much higher oil pressure, probably due to new bearings. It seems to work just fine.

 

[Coach]

Joee12, thanks for the info. I have a drain line that comes off the oil pan.
I'll give Blackstone Labs a call and look into the kit
Thanks again for the info
Coach

 

[SCL]

I recently changed the oil in my 3 liter Mercruiser with the recommended Mercruiser Quicksilver 25-40 multivis. I have used 40 weight oils in the past as well. I am in South Carolina and have both Florida like weather and also run in cold weather at times. Any thoughts about which I should go with overall?

 

[joee12]

SCL, welcome to the forum!! I think that the Mercury oil you chose will do just fine.

How's the fishing in Charleston?? Last time I fished there(March 01) the red drum were hitting pretty good in front of FT Sumnter. -Joe

 

[SCL]

Joe, I didn't do too good fishing on 4/25/03 but was not at Fort Sumter. I was in the Folly River and off Kiawah. I just got my boat back from some minor repair that needed done, so have not fished much since last fall.

Thanks for your input on the oil. I assumed that Mercruiser knew what to recommend for their engine and it costs only a little more, so I went with it.

What about filters? Does that make any difference to a boat with it's harsher demands than my car engine? I have visited Bob's filter flow experiment page.

Ed

 

[joee12]

SCL, unfortunately, I never cut open any Boat filters to see who made which ones. I useMercury filters on my brother's 3.0 Mercruiser. I need to cut the next one open to see what it looks like inside. I need to spend more time researching them. -Joe

 

[1 FMF]

Joe, for the 3L merc 4cyl, you can use the AC delco PF35 filter as a replacement. The pf35 is a longer filter, I don't remember what the AC # was for the same length replacement.

I aquired a 2002 bayliner 19' end of last summer, it has the 4cyl 3L merc i/o. I did oil analysis on the factory oil, merc 25w40, using dyson analysis. I think you might still be able to find the report in the UOA section. The oil sheared right into a 30wt oil. But for what it's worth I do a lot of slalom skiing with the boat so the motor runs at 4k most of the time and it is also new so the shearing may also be attributed to break-in somewhat. I think I put somewheres around 10 hours on the engine when I got the boat before changing the oil, and I figure the previous owner put no more than 5 hrs on it from when he got it brand new.
I have a gallon of merc 25w40 my neighbor gave me so I hope to use that for part of this upcoming season then do another analysis on it.

On my 24' formula, 1976, I have a factory new ford 351 I dropped in back in 1993. I ran redline 10w40 synthetic in it last season from June to December here in CT. Oil analysis showed it held up excellent, low wear, stayed in viscosity, and had a good TBM report. That motor spends most of it's time at 3k rpms but sees occasional 3500-3700 from skiing, until I got the bayliner.

 

[joee12]

I FMF, thanks for the AC Delco number, I'll save a few bucks on that one. It is good to see some analysis on boat oil, thanks!! -Joe

 

[Schmoe]

AC/Delco PF 25 for the short
PF 35 for the long