5-40 Rotella Synthetic in Inboard and IO Boats?

[callbay]

I know I have read several threads on this, one on using it in racing boats but I can't find the treads. I put "5-40 Rotella in boats" in the search and nothing came up on boats in 7 pages.

Anyone have the thread links or new info on this?

Thanks!

 

[paulswagelock]

I had a conversation where another user was using Rotella T6 in his Volvo 8.1, that is the only conversation I ever remember along these lines.
Generally, I think it would be a decent choice. However, I do not know that it would offer much benefit over the myriad of 15w40 choices you have from Shell, Chevron, or Mobil at half the price of T6.
What is your basis for wanting to use rotella 5w40 T6 in your boat?

 

[callbay]

Originally Posted By: paulswagelock
I had a conversation where another user was using Rotella T6 in his Volvo 8.1, that is the only conversation I ever remember along these lines.
Generally, I think it would be a decent choice. However, I do not know that it would offer much benefit over the myriad of 15w40 choices you have from Shell, Chevron, or Mobil at half the price of T6.
What is your basis for wanting to use rotella 5w40 T6 in your boat?


My son just bought an old 1991 Deep V boat with a 5.7 Mercrusier I/0. He runs the engine very had like 4,000 rpm and higher at cruise so I want the best possible protection I can get for him.

Thanks.

 

[paulswagelock]

I do not have the 1991 Merc manual, but I would bet they were recommending a straight weight 40 oil back then. I believe the API classification back then would have been SG, so I believe 1200-1300 ppm of Zn and P. So, I would recommend you select a robust oil, very sheer stable, with lots of Zn and P. That would normally be HDEO, racing oils, or boutique oils. Ones that come to mind would be any of the 15w40 dual rated oils, the syn 5w40 dual rated oils, Brad Penn race oils, Mobil1 15w50, likely the Amsoil marine 40 wt oil, Royal purple marine oil, and maybe a few others.
Typically synthetic oils are for extended drain intervals. I would not recommend extending a boat oci beyond 100 hours, and that might be pushing it.
My only concern would be shear stability of a 5w40 oil at a highly loaded 4000 rpm. I had Merc brand oil 25w40 shear to a 20 wt in 50 hours of easy use on a modern engine with fuel injection. I do not have any experience with the shear stability of the T6, hopefully someone can chime in with some facts around that.

 

[cchase]

I still can't get my head around why marine engines were so stubborn specifying straight-weight oils back 15 years ago.

I run synthetic SAE 30 in my 4.3 and it shears deep into a 20wt after about 20 hours.

 

[dr2152]

I've ran Rotella 5-40 for 200 hours in my 5.7L. I change it very two years or 50 hours. If it can take the punishment of my diesel car and the Harley it is fine for the boat.

 

[lars11]

There are several threads about this and it lines out as this:
1. The engines work very hard in boats, hours near wot and never ever downhill, and this calls for fairly heavy oils SAE 40 or 50 at temp.
2. The engines are typically also dumping too much fuel during the run cycles (less with electronic controlled injection)
3. They shear oil a lot when running, v6 seem to be the worst.
4. Even with all that water cooling the engine, some oil passages turn very hot so it needs even more visc stability to lube right.

So, what does the makers recommend?
Volvo says 15w50 mineral until like 2004 (Gxi), then 15w50 synthetic. In some cases straight sae30 synthetic is also on the list (Amsoil)
Mercruiser says 25w40.
I think both recommend 50 hrs oci, 100hrs oci on the very newest engines with synthetic.
At 50 hrs the engines have burnt appr. 2000 liters of fuel (at nearly wot...) so it would equal a 1 year oci at 20000km on a medium car.

I think that the risk for fuel dilution and shearing making the oil thinner is why stout oils with less VI improvers are preferred. Then there is seldom a need for better cold starting either so a 5w-X is not on the list even if your 5w40 would probably do just fine at least when fresh and strong...

I run a volvo 5.0Gi on Mobil Delvac MX 15W-40 and oci of 40-50 hrs and see stable pressure all season.

Seriously, buy rotella, delvac etc. 15w40 or merc 25w40, change often and be happy. If you get a deal buying bigger packs of merc 25w40 get that instead. There is not much to gain from synthetic and low visc oils in a marine v8.

And for the wise comments:
- They are all car engines and will do well on cheap 10-30. Nope, unless you are oozing it along in a canoe which is like truck use.
- The diesels are worse on oil so the simple lo saps lo protection stuff will do as well. Nope, diesels are not necessarily worse on oil, but they are different.
- You need to use the manufacturer oil. Nope, not for the engines. But some duoprop outdrives are picky on oil. Beware.

 

[HerrStig]

I had a savy friend with an ME tell me that inboard marine service, if the engine was properly designed for it, at constant load was not that tough. Boat engines don't often see stop and go service. There is usually plenty of cooling available for a boat engine, if a properly designed water to water heat exchanger is used. The many things that can be fudged with a built to a price automotive conversion can change the equation. Watch the guages. If the temp and pressure gauges are stable at crusing speeds it is a pretty good sign that the cooling is properly spec'd. One problem with marine service is OVER cooling. With a car you have the thermostat AND electric cooling fans to modulate, in a boat you pretty much have to depend on the thermostat, and the water temp you operate in can change quite a bit from a harbor to open water. Obviously, the less VI the better in any service.

 

[lars11]

That's right, temp is not the main issue unless you have a problem with the rig. But still, local oil temps, engine strain and pumping lots of fuel makes these different from other engines. I have the 5.0 volvo version GM 250hp with Volvo TBI and it has a VOT of 4900 rpm and cruises for hours at 4000 rpm, pretty close to max output. That's not something you do with any car.

Example:
Volvo recommends 15w50. They genererally do not have oil coolers.
Merc recommends 25w40. They do generally have oil coolers.
So I do still think oil temp is a real issue even if cooling water temp is not.

Then these are old design blocks and they have some quirks that you cannot ignore.

But if you take an optimized engine design, like you say, you will see more normal recommendations. An new design 250hp 4T outboard wil for example use a small amount of 10w30 full synthetic lube with much longer OCI than the inboard v8's 5 liters and 50 hrs. Same with diesels converted from industrial engines, they see similar use in the boats as they do in the original generators, long haul heavy trucks and so much more normal recommendations.

 

[SteveSRT8]

There is no more mechanical shearing in a boat motor than in a car motor, especially in a V8/V6 taken from a major car mfgr.

The major culprits working to shorten oil life are overcooling and fuel dilution. Short OCI is a must, but not because the duty cycle is harder. Only the average rpm is higher, the load is actually less than when mechanically coupled to a road. The peak rpm is usually limited to quite a bit less than the exact same engine in a vehicle.

As with any car, steady high rpm operation at light load equals very easy duty and little wear if properly cared for.

 

[cchase]

I strongly disagree with the assertion that the load is lower in a marine application than when mechanically coupled with the road as in a car.

 

[SteveSRT8]

Just think prop slippage and it'll come to you.

A car is mechanically linked to the road, whereas a propeller slips and slides until you get close to peak rpm. Most boats never run there much, and the designers of lower units are the ones who developed the data decades ago.

Frankly just the sizing of the output shafts in the driveline of a boat tells you a lot about the loading.

Continuous high rpm operation hurts nothing in a properly maintained, healthy engine. And marine motors have reduced redlines compared to street motors.

 

[cchase]

I'm thinking of this from the perspective of required horsepower or watts, energy output. It requires a LOT more energy to push a boat through the water than it does a car. This tells me that somehow the loads are higher.

A car running 65 mph down a level highway with no wind is likely using 2 gal/hr of fuel. A boat with a similar horsepower engine is likely using 10-15 gal/hr. There's no way all that extra fuel is not being burned, and thus I struggle to see how the load on the engine is not higher. Energy in has to correspond to energy out, and higher energy levels correspond to higher load levels in an internal combustion engine.

Right?

 

[lars11]

I am not at all sure about the lightness of the load pushing a 6000 lbs boat through water at 4000rpm compared to rolling a 5000 lbs truck at like 2000 rpm with some downhill and tailwind too...

But maybe that difference is less noticable in the v8. But I know for a fact that other engines that are known to be bullet proof in cars suddenly are borderline in boats, like the Volvo 3 liter I6, the GM 4.3 V6 and others. They just seem to be on the limit, sensitive to cooling, busting head gaskets, crooked heads, sensitive to oil (4.3) etc.

 

[SteveSRT8]

It's not the AMOUNT of load, it's the NATURE of the load.

Very low shock loading on a boat engine versus a car.

Pick a similar weight car and boat with similar sized motors, the boat engine has an easier job than the car motor does. Consistent rpms, smooth driveline loading with no shock, unlimited cooling, no shifting gears, etc.

The duty cycle is easier.

 

[cchase]

I would agree that the shock load is lower and the overall engine load is higher. Just looking through the site at UOA's from boats tells me that for whatever the reason, they shear oil much more than the same engine does in a car.

I've never seen data that would show a connection between the shock loads a car engine sees and engine wear. I'm not insinuating that there is none, I just have never seen it. It would certainly add a whole other variable to comments in the UOA section of the site if cars with manual transmissions or variations in shift programming affected vehicle UOA.

 

[JAG]

I've seen test data online showing wear rates as a function of time while the engine was in gear and during transmission shifts and it showed a spike during shifts. Over-cooling of an engine is definitely a negative since the antiwear additives don't work as well at low temps. and the higher amounts of fuel and water dilution in the oil also reduce the effectiveness of antiwear additives. Over-cooling may also put higher thermal stresses on the engine due to bigger temp. differences between various parts of the engine than an engine in a car experiences. High RPMs obviously shear the oil more which will break apart polymeric viscosity index improvers more quickly.

 

[SteveSRT8]

You would see a load of data if it was still available. Autos versus manuals is a great example.

It was always customary to deduct $$ for a manual at trade in. Also manufacturers used to have a much higher incidence of warranty repairs on manuals versus automatics. Manuals buy more driveline parts and have more engine claims under warranty.

This data is not apparent by looking at one car, only by looking at thousands, so it really does not apply to the individual.

The shear in boat UOA's is not from being mounted in a boat. The engines are mechanically identical. I think you'll find that the typical smaller boat engine is doing more work than it does in a car due to boats being so heavy and high drag, etc.

 

[friendly_jacek]

Lars11,
excellent data. I would only add one thing. Some people use 5W40 thinking it's better than 15W40. It's not, it has lower HSHT (by SAE definition) and shears down more.

 

[cchase]

Originally Posted By: SteveSRT8
You would see a load of data if it was still available. Autos versus manuals is a great example.

It was always customary to deduct $$ for a manual at trade in. Also manufacturers used to have a much higher incidence of warranty repairs on manuals versus automatics. Manuals buy more driveline parts and have more engine claims under warranty.

This data is not apparent by looking at one car, only by looking at thousands, so it really does not apply to the individual.


I think we can both agree that deductions in manual trade-in value have little to nothing to do with wear rates or shock loads as a function of design. Same goes for replacement parts and engine claims. That's poor driving, which it is certainly easier to damage a manual drivetrain through abuse.

I suspect you won't find a real-world difference on engine wear between a manual and automatic transmission, assuming they are being used within design parameters

Quote:

The shear in boat UOA's is not from being mounted in a boat. The engines are mechanically identical. I think you'll find that the typical smaller boat engine is doing more work than it does in a car due to boats being so heavy and high drag, etc.


This was the point I was making initially, hence my comment earlier,

Quote:
I strongly disagree with the assertion that the load is lower in a marine application