Engine Oil

Mar 18, 2014
12
Catalina 30 Vancouver
I'm getting some conflicting suggestions on replacing my engine oil.

My engine is a Universal M3-20. The manual suggests SAE 30 (in warm weather) or 10W40 (in hot or cold).

I had trouble finding 10W40 so I asked a diesel mechanic who said I should be using 15W40.

I later came across some 10W40 oil but was told by a store worker that it was not for diesel engines (the oil itself says nothing about being for gas engines only)
https://www.walmart.com/ip/Castrol-GTX-10W-40-Motor-Oil-5qt/17175670

Am I getting good advice? Should I ignore the suggestion of my manual and go with 15W40? I
 
Nov 18, 2013
171
Catalina 310 Campbell River
Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to deal with them. When you put this extra additive load in a gasoline engine, the effects can be devastating to performance. The detergent will work as it is designed and try to clean the cylinder walls. This can have an adverse effect on the seal between the rings and liner, resulting in lost compression and efficiency.
 
Oct 26, 2010
1,881
Hunter 40.5 Beaufort, SC
You can get Rotella T 15W-40 at about any auto parts store and at Walmart, etc. It is formulated for diesel engines (as are many other brands like Delron and others). I use it in all my diesels but then again, I live in South Carolina, not the frigid north. Maybe the 15W is too viscous for winter starting in Vancouver, but then again, I would think you wouldn't be sailing much in sub-freezing temperatures anyway. If you're starting and running your engine in water temperatures then the 15W should be fine. That's just my 2 cents, your mileage may vary.
 
Jan 5, 2017
2,263
Beneteau First 38 Lyall Harbour Saturna Island
I always used 15/40 in my 5411. If it's for diesels it will say so on the can. It's a modified Kubota tractor engine when you need spare parts. Diesel oils also have EP additives to withstand the higher compression ratio's
 
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
David

15W40 is going to be fine. You will not see motor use at temperatures so low that 10W gives you any help (the W= winter.)

Pay attention to the API designation - printed on every container. Use C rated oil - (CH CI CJ) . C designates use in compression ignited fuel (diesel motors) not S which designates oil for spark ignited fuel (gasoline motors.) No reason for full synthetic. Regular old dino is fine.

Charles
 
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May 20, 2016
3,014
Catalina 36 MK1 94 Everett, WA
I use Delo 400LE 15W-40 --- I pay enough in electricity that I'm not worried about the motor be extremely cold that it would require 10W. As with any detergent oil - If it going into an engine that has been running non-detergent be sure and do an accelerated oil change cycle following the change.
 
Oct 22, 2014
20,989
CAL 35 Cruiser #21 moored EVERETT WA
David. These writers hit it out of the ball park. You and they are in the Pac NW and they nailed it. GO forth and change your oil with confidence.
 
Aug 1, 2011
3,972
Catalina 270 255 Wabamun. Welcome to the marina
Put a load of Rotella in it, and enjoy how much better it runs. I run the stuff exclusively in my truck too, and although you guys have us beat for snow this year (ha ha) we still got you on cold.
 
Oct 22, 2014
20,989
CAL 35 Cruiser #21 moored EVERETT WA
Yes Meriachee... You can have your cold. And if you like take the snow as well. I can deal with rain... I can deal with snow.... But when all of it comes at the same time and decides to stay it can get to be to much.... Last winter like this was in 1970.
 
Jun 15, 2012
694
BAVARIA C57 Greenport, NY
Rotella also makes a synthetic rated at 5W-40. Might be just right for the cold weather starts. I use this oil in my engine and generator with no problem.
 
Jun 19, 2004
365
Island Packet IP 32 99 Forked River, NJ
Our engine: Universal M3-20. Using Rotella 15W-40 from Walmart. 800 hours and counting... no problems.
 
Nov 14, 2013
238
Catalina 30 MkI 1983 TRBS Westbrook, CT
Another vote for Rotella 15W-40 here. Used it for years with no issues.