350 Mpi Losing Oil

[CheapboatKev]

Re: 350 Mpi Losing Oil

I envy you Salt, I just ahd to go out and move a couple boats around to make some room and the trailer tires were frozen solid to the ground.

Yikes! Was a terrible 80 degrees down here today! Had to have the AC on in my office! Wish y'all could spend a winter down here on the Gulf!

 

[SEA SALT]

Re: 350 Mpi Losing Oil

Hi Guys.

Found the attached tests results for my boat:

SPECIFICATIONS
LOA: 35'6"
Beam: 11'5"
Draft: 2'9"
Weight: 13,200 lbs.
Fuel capacity: 200 gal.
Water capacity: 40 gal.
Test engines: 2/300-hp MerCruiser VD-350 Magnum MPI gasoline V-drives
Transmissions/ratio: ZF 63 IV/2.00:1
Props: Hall & Stavert 18x19 3BC Nibral

They do not show torque or anything like that but they do show fuel consumption at different RPMs which sort of relates to the efficiency of the engine/prop combination. The test says that they planed the boat at 3000 RPMs and once you hit planing speed, the most efficient seems to be at around 3500 RPMs.

At 3800 to 4000 RPMs I realize we sacrificed fuel efficiency to gain a little more speed...late November weather in that area is prone to high winds.

Anyway, thought that was interesting and worth sharing.

Thanks again,

SEA SALT

 

[QC]

Re: 350 Mpi Losing Oil

That actually shows her as more efficient from 4000 to 4600 . . .

 

[SEA SALT]

Re: 350 Mpi Losing Oil

You are right.

I think for long trips like that though, an oil cooler would be a good idea and will look into it. Do you think that maybe sinthetic oils would handle the heat any better and thus avoid the need for oil coolers?

Thanks

 

[QC]

Re: 350 Mpi Losing Oil

I am not 100% sure that oil coolers will solve oil consumption issues. I am not 100% sure that your oil is getting too hot either. I don't think oil coolers would be bad, but I don't think we have enough good solid data to indicate any solutions yet. I don't think we have enough good solid data to indicate any problems yet. Ideas for making things improve? Maybe. But solutions will need to be based on good, solid data and frankly I have no idea what "acceptable" oil consumption would be on these engines. Based on my own experience, when running them hard I wouldn't be totally freaked out at a Qt. every 10 -15 hours. I woudln't like it, but I wouldn't lose a whole lot of sleep over it.

I do think you were a LOT heavier than that test data. Is that data from your boat? Sister ship? Do you know how fast they will spin at WOT in your boat now? Let's say they would only run 4200 at WOT under the load you were carrying on your trek. If so, then cruising at 4000 RPM may in fact be the entire problem. My earlier comments were intended to say that we cannot categorically say that 4000 RPM cruise RPM is bad. We cannot say that 4000 RPM is too highly loaded either. We can say that IF your boat will only run 4200 RPM at WOT as it was loaded (I don't know, you'll have to tell us) that in that case 4000 RPM cruise would be less than good, and may cause higher than normal oil consumption.

I hope you understand that the only way to base any of these discussions is on reliable, repeatable data. For me that would start with WOT RPM at a normal load. And I would like to compare that with WOT RPM under the conditions you experienced what appears to be high oil consumption.

My signature used to be: In God We Trust, all others show us your data . . .

 

[SEA SALT]

Re: 350 Mpi Losing Oil

Hey QC...I think you just hit on the problem we encountered.

The boat test was for a sea ray 320 SD spec'd just like mine. They indicate a maximum RPM of 4600 and 31.9 Knots, while we were hitting a WOT of 4250 RPM and 27 Knots, surely due to the much heavier loads we had as compared to the test boat.

We did run the boat at 3800 to 4100 RPM quit a bit and that perhaps or most likely caused the oil consumption. That was a lot of hours at near WOT.

Appreciate the comments on the oil coolers and such. One thing is clear though: I understand the need to keep oil on board and to be checking it every trip.

I just never had to worry about that kind of stuff on my Johnson two stroke (other than refilling the oil reservoir) and as with everything else in life, I just need to adjust myself to the needs of the new engines...lack of understanding is a dangerous thing, isn't it?

It is great to be able to chat with you guys about all this and the more I do it the more I like it.

Thanks again QC.

Best regards,

SS

 

[Don S]

Re: 350 Mpi Losing Oil

The boat test was for a sea ray 320 SD spec'd just like mine. They indicate a maximum RPM of 4600 and 31.9 Knots, while we were hitting a WOT of 4250 RPM and 27 Knots,

Right there is why the engine was working so hard. With all the extra weight on the boat, you were seriously over propped. You might even be over propped with normal weight. Have you ever checked? Being over propped is one of the wrost things you can do to your engines. You might consider a different set of props for those seriously long, heavily loaded trips. Props are a lot cheaper than new engines.

 

[SEA SALT]

Re: 350 Mpi Losing Oil

Thanks Don.

The thing is, the boat is factory spec and therefore it makes me wonder if the Sea Ray engineers got the props wrong...I would tend to think that a company as reputable as Sea Ray would not make a mistake like that on a boat that size. That is not to say that big companies don't make mistakes on their products but that would be a very basic mistake would it not?

 

[Don S]

Re: 350 Mpi Losing Oil

Sea Ray can only do so much with props, they have no idea how heavy the boat will be, or altitude or anything like that. They know what prop it takes for how the boat was designed, but it's up to the owners to make sure they are propped right with their normal load where they normally boat.

You might want to post over in the prop forum and see if you can find out what size props you really need.

 

[SEA SALT]

Re: 350 Mpi Losing Oil

Thanks Don.

I think I will leave the boat as is for now since we will rund the boat under normal loads and will instead do a little research on propper prop sizes for different load scenarios. Then, for my next long trip we will be prepared and I agree that props would be far cheaper than new engines...no doubt.

Best regards,

SS

 

[QC]

Re: 350 Mpi Losing Oil

We did run the boat at 3800 to 4100 RPM quit a bit and that perhaps or most likely caused the oil consumption. That was a lot of hours at near WOT.

I think even the test boat was overwheeled . . . I can't find the suggested WOT RPM for the inboards, but the I/O version of that engine is 4800 - 5200, so I am guessing they are at least two inches too big.

I also can't belive we never asked what WOT RPM you were hitting . . . We danced around it, but never got there

 

[Don S]

Re: 350 Mpi Losing Oil

Inboard rpm range is 4400 to 4800. Not that far off. Probably just the extra load.

 

[QC]

Re: 350 Mpi Losing Oil

Then the test boat was dead nuts, which is always a problem as they gain weight the day the go home . . .

 

[SEA SALT]

Re: 350 Mpi Losing Oil

I found another test, this is what they say:

Test Power: 2 x 300-hp MerCruiser 350 MAG MPI RPM MPH Knots Total GPH MPG NMPG Range NM Range dBA
1000 6.1 5.3 2.4 2.52 2.19 454 395 64
1500 7.9 6.8 5.0 1.57 1.37 283 246 69
2000 9.9 8.6 9.2 1.08 0.94 194 168 72
2500 11.3 9.8 16.4 0.69 0.60 123 107 77
3000 15.6 13.6 21.0 0.74 0.65 134 116 78
3500 24.8 21.6 26.2 0.95 0.82 170 148 82
4000 30.2 26.2 33.4 0.90 0.78 162 141 84
4500 34.3 29.8 40.8 0.84 0.73 151 131 86
4950 35.4 30.8 41.4 0.86 0.74 154 134 86

Speeds measured with Stalker ProSports radar gun. Fuel consumption (gallons per hour) measured with Floscan digital fuel-flow meter on gas inboards, sterndrives, and outboards, TechMate electronic scan tool on gas EFI inboards, Caterpillar digital fuel-flow meter on diesel engines, or permanently installed fuel-monitoring equipment. Range is based on 90% of published fuel capacity. Sound levels determined using Radio Shack digital decibel meter on A scale. 68 dBA is the level of normal conversation.

Performance Chart

Test Conditions
Test Power: 2 x 300-hp MerCruiser 350 MAG MPI
Time To Plane 5.1 seconds
0 to 30 16.8 seconds
Test Power 2 x 300-hp MerCruiser 350 MAG MPI
Transmission Hurth
Ratio 2.0:1
Props 17 x 21 3-blade Nibral
Load 4 persons, 1/4 fuel, no water, min. gear
Climate 63 deg., 68% humid., wind: 15 knots; seas: 1 foot

 

[Don S]

Re: 350 Mpi Losing Oil

I wouldn't get all concerned with "Test Reports" they seldom tell you real world numbers. About the only thing it tells you is the MAX you will ever get and your REAL numbers will be less.
Boaters seldom go out and have fun the way tests are done. We get to idle through no wake, actually put stuff on the boats, and have waves, weather and other boaters to contend with.