Replacement recommendation for Mercruiser 25-40

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Looking for a synthetic to replace Merc's 25-40. I have currently narrowed down my list to these oils:

-Mobil Delvac 15-40
-Mobil 1 15-50
-Mobil 1 0-40
-Amsoil 15-40 Marine/Diesel
-Shell Rotella T Synthetic 5-40

Anyone have a favorite for Mercruiser I/O application -- either V6 or V8? The M1 15-50 would certainly be the easiest to get.

I have a 2700 lb boat with a 220 HP Mercruiser 4.3L EFI V6 that works pretty hard. WOT gives 4800 rpm. I stay under 100 hours per season.

Gitw
 
Schaeffers 7000 blend 15w-40 is a good add match for that oil spec and will exceed the need and the poor quality of the merc oil.

Redline 10w-40 for a full syn application.
 
I can only comment about the Amsoil 15w-40 ....

I have customers running this oil in the 5.0L and 7.4L Mercruiser inboards. It holds up very well. My 37' SeaRay customer with the twin, 454 inboards is running 150 hour/1 year change intervals and still seeing TBN's in the 9-12 range.

My second choice would be delvac 1, from AVLube - one of the site sponsors.

Ted
 
The oil works fine, but it's 100% more expensive than it should be ...You can buy a 5w-40, GP III synlube for $3.00/qt, at least in Canada ....

Tooslick
Dixie Synthetics
 
Shell tried marketing a marine 25W40 and it fell on it's face. I still have some of it around only because it was cheap and on sale.
Delo 5W40, or one of the many HDMO XXW40s including Rotella, would be a much better choice than the Merc 25W40 if its anything like the Shell stuff was.
 
I have decided to try Amsoil Series 3000 5W30 HDD. I have been using Amsoil 15W40, but the oil pressure runs on the high side, which makes me nervous. My boat is run mostly on the weekends, and sees more idle than cruise, so I think I am better served by the 5W30. As an added bonus, I can also run this oil in my car year round, so I only need to stock up on one oil.
 
This is an interesting thread.

You ask for input, got plenty of good advice, and then made the decision to use an oil completly out of spec and one that wasn`t even mentioned at the beginning, but probably will be fine the way you use your boat.

I would still use the Amsoil 15W-40 if it were me, If not a synthetic, the Dellow 15W-40 would be my next choice.
 
quote:

Originally posted by Hasbeen:
This is an interesting thread.

You ask for input, got plenty of good advice, and then made the decision to use an oil completly out of spec and one that wasn`t even mentioned at the beginning, but probably will be fine the way you use your boat.

I would still use the Amsoil 15W-40 if it were me, If not a synthetic, the Dellow 15W-40 would be my next choice.


Hasbeen - Who are referring to?
 
I'm pretty happy with the Pennz. 15W-40 LL. Idle and WOT are all around 40 psi. Oil has only about 5 hours on it so far, see how it holds up by the end of the season. I wish I could say the same for my Comp Prop that got the be-jesus beaten out of it Saturday afternoon....
frown.gif
 
I should point out that my motors (Volvo Penta 5.0) calls for 30 Wt synthetic. Thus, I am not far from spec. Although this engine is the same basic GM motor that Merc uses, I am wondering if there is something different in the oil system as a 15W40 oil results in 70 PSI on the oil gauge while 30Wt results in a much more reasonable 40-60 readings.
 
quote:

Originally posted by DockHoliday:
I should point out that my motors (Volvo Penta 5.0) calls for 30 Wt synthetic. Thus, I am not far from spec. Although this engine is the same basic GM motor that Merc uses, I am wondering if there is something different in the oil system as a 15W40 oil results in 70 PSI on the oil gauge while 30Wt results in a much more reasonable 40-60 readings.

What are your pressures when hot? I would think the 30w is more stable and not fluctuate as much.
 
The pressures with the hot 15W40 is around 70 PSI (gauge is hard to read to get an exact numeric reading). The 30W runs noticably lower when hot. Could just be that Amsoil tends to be on the upper end of each Viscosity rating.
 
'94 4.3LX: I have used M1 15w-50 for 10 years (1.5 seasons in storage). Easy 100+ hours season. No problems, no sludge, clean motor. Air temp here in mid-high 90s typically and water in mid 80s. Oil pressure between 43-60ish psi at any rpm above 2000 on hot engine.

I do get some drop in pressure in bumpy water or start/stop (this is the 43 psi min from maybe 5 or 7 psi higher). This could be due to the oil getting aerated a bit. You could look for an oil with anti foaming additives. Perhaps Amsoil 15w-40 Marine has an additive (silicon?). The local marine dealers sell it here.

My goal would be to put an oil in there with no viscosity improvers so you don't get sludge/varnish on the hard working marine engine or worry about shear over time..don't know if this is true for M1 15w-50, but results appear to bear this out.

I'll get an analysis done at end of season and post.
 
Powerboat magazine had a question about thick or thin oils in the August issue. The reply was to use a straight 30 weight oil or a 25w-40. That a multi-grade would lead to sticky rings. Also, raw fuel enters the crancases in boats and dilutes the multi-grade oil, but not a straight weight oil. How would this lead to sticking rings? I guess the fuel dilution makes sense.
 
Well, I drained the Merc oil from my boat yesterday and caught a sample that I will be sending off. It had 53 hours on it. I thought of going all season -- estimated to be 100 hours, but I couldn't do it
wink.gif
. The UOA will be interesting to me to see how this little engine beats up oil.

I was dropping used oil off at a local oil change spot called Oil Etc. They had Amsoil 15W40 Marine oil in stock for $6 a quart. So I bought 5 quarts.

I hate to use the good stuff for the remainder of the season. I may winterize with the Amsoil (to use all next season) and use a Chevron Delo 15W40 HDEO for the next ~50 hours.

Decisions, decisions.
 
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