engine oil change

S

srdancer90

Member
May 2, 2008
121
North East
Boat Info
340 Sundancer
Engines
8.1 496 Mercruiser inboard
I live in the north east, and have used Shell Rotella straight 40 weight oil. As this is difficult to obtain, I was told by a Shell tech that I could use the Rotella 15-40 oil. My question is at what temp will the multi vis oil reach it's 40 weight. My engine runs at 158-159 all day, and takes 5-6 min to get there, so am i safe to say that the oil is not at 40 before the full operating temp range.The shell tech said that the start up will have better protection with the 15-40, yet I am wondering if the time it takes to reach full operating temp will not allow the oil to be at the required 40 weight range and will eventually harm the engine. any advice on this.
2004 320 Da T/5.7 350 mag mie
 
OK, I'm going to expose my ignorance here, but why are you using diesel oil in gas engines ? and a straight 40w ? Just in my very layman mind it seems like it would cause harm....
 
"Shell Rotella T oil is formulated for diesel engines. Available in multigrade 15W40, and single grades SAE30 and SAE40. Shell Rotella T meets or exceeds most marine diesel engine manufacturers requirements including Caterpiller, Detroit Diesel, Cummins and Volvo.

Single Grades SAE30 and SAE40 are formulated to endure the rigorous use of diesel engines. Multigrade 15W40 is suitable for hard working 4 stroke gasoline engines of marine engines, passenger cars, trucks, SUVs, minivans and motorcycles. It is also suitable as an all season oil for certain diesel engines. "

Source: http://www.jamestowndistributors.com/userportal/show_product.do?pid=8423
 
Mercury recomends 25W40 oil meeting NMMA FC-W standards for four-cycle engines. You should have acceptable results with 15W40, 15 weight is a little lower than I would go, but it shouldn't really cause any problems. You may notice slightly lower oil pressures especially when cold, but thats about it. Once you reach operating temps it should perform about the same as the slightly heavier 25W40.
 
Here in lies the problem, the 15-40 arives at it optimal vis at 200 degrees,( as per the chart from the previous post) my engine operates at 160 degrees max. will I have a problem with the 15-40 because it has not reached the optimal heat range for the 40 vis to be available? Acording to the tech the straight 40 has issues at start up because it lacks the lube requirements of the 15-40. It is confusing?
 
The main problem with multi-viscosity engine oils is viscosity index improver breakdown. Re-read the article. Under conditions of stress and load VI improvers tend to break down leaving only a lower viscosity oil. Thus a 15W-40 would degrade to a 15.

Marine engines work much harder than auto or light truck engines. You don't normally run your car with the throttle half way or two thirds of the way open for hours on end, but your boat's engines do run that way. More load means more pressure on the rings and bearing which tends to shear the VI improvers. I believe that's why Mercury did not recommend multi-viscosity engine oils. The 25-40 oil is a blend. It uses no VI components.

Best regards,
Frank
 
srdancer90 said:
Here in lies the problem, the 15-40 arives at it optimal vis at 200 degrees,( as per the chart from the previous post) my engine operates at 160 degrees max. will I have a problem with the 15-40 because it has not reached the optimal heat range for the 40 vis to be available? Acording to the tech the straight 40 has issues at start up because it lacks the lube requirements of the 15-40. It is confusing?
Click to expand...

Dancer90 - your water temp is 160, but your oil temp is probably in the mid 200's...after your engines are up to operating temperature...
 
The key to the diesel oils are they will not shear like the automotive oils. Rotella and Delo 400 15w40 are some of the best HD oils out there for gas engines. The 25w40 merCruiser oil is just not worth $7 a quart IMHO when running an 8 quart oil pan, Mike.
 
CV-23 said:
..... The 25w40 merCruiser oil is just not worth $7 a quart IMHO when running an 8 quart oil pan....
Click to expand...

IMO, following recommendations provided in your manual is the best and might be cheapest, in the long run, approach. This might play a bigger role for newer boats that are still under the warranty, so you don't void them by not following the manual.

Obviously, there're plenty of good and competative products out there, so if you'd like to switch to other brand of your preference at least use the same parameters. In example of oil Quicksilver 15W-40 or 25W-40 could be supplemented by Delo 400 Motor Oil SAE 15W-40 or any other brand you like that meets the parameters.

My point is that saving $5-$10 on the maintenance of critical components of the boat is not worth the risk.

As with anything there are always exceptions. So, in case when a manual says change part A123 made by brand ABC and this part is actually made by brand XYZ that was relabled (e.g. Sherwood water pump), I would go the original XYZ brand, which most likelly be less money and perfomr exactly the same.

Just my .02c.
 
Last edited:
CV-23 said:
The key to the diesel oils are they will not shear like the automotive oils. Rotella and Delo 400 15w40 are some of the best HD oils out there for gas engines. The 25w40 merCruiser oil is just not worth $7 a quart IMHO when running an 8 quart oil pan, Mike.
Click to expand...

The West Marine by me sells a Gallon of the Merc oil for about $22
 
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