Does anyone know the best RPM to operate a marine diesel. Some guys told me to open them up. Not really sure how to get the best mileage.

Depends on the type of boat. If you have a way to monitor fuel consumption, (ie gals/hour)...create a graph of rpm vs speed and note fuel consumption at each data point. You will find the sweet spots (ie optimal mpg). Belive it or not, it will be at a different speed than you think.
FloScan makes a gauge to compute real time MPG (it uses fuel sensors and input from a GPS)

I would never run any engine wide open for an extended amount of time, diesel or gas. Like said above flo scan is great. If I'm driving a boat stay around 2/3 to 3/4max throttle. that also depends on the sea state, but for the most I get it up on a plane then give it a little more. The difference in fuel economy is huge with just a few RPMs over cruising speed, relatively speaking.

Really depends on which diesel you have.
Some are designed to run at lower RPMs (cat,mac,cummins ect..)
My Yanmar is a higher rpm diesel.
They want it run at 90% most of the time and don't like extended periods of idle (trolling)
I run my 315 @ 3000 - 3200 most of the time at cruise,. best speed + economy for me @@ 5-7 gph.
I max out @ 3900

Duke,

What are you really looking for? If it is what the engine likes Diesels want to run loaded. Like Ronnie said 90%. This creates the best combustion, fuel air mix, more boost air for better fuel economy. I am not talking gph, just what the engine likes. Lots of trolling on a diesel, not good in the long run.

That 90% figure is cited in many owners manuals as well as the maximum % of time at wot. Befor you start running 90% make sure your engine turns it's rated rpm at wot.
As most have mentioned, Best fuel Economy is a function of hull type, various engine parameters, prop type and size, loading etc... That is why I suggest you figure out where the sweet spot is using a gauge. Some engines have computers built in that have a NEMA 2000 bus that sends fuel consumption data and you might be able to display this in a chartplotter data window. Otherwise something like a flowscan meter works, but they are a pain to install and even more of a pain to calibrate, but they are accurate. They keep track of all kinds of fuel data.
Posted from my iPhone/Mobile device

Does anyone know the best RPM to operate a marine diesel. Some guys told me to open them up. Not really sure how to get the best mileage.

0 rpm would be the best efficiency.:biglaugh:

that depends who's paying for the fuel. :bo:

Duke,

What are you really looking for? If it is what the engine likes Diesels want to run loaded. Like Ronnie said 90%. This creates the best combustion, fuel air mix, more boost air for better fuel economy. I am not talking gph, just what the engine likes. Lots of trolling on a diesel, not good in the long run.

Extended amount of time is bad on turbo more than anything.
Turbo washes are very important.
I did oil change and all fuel filters yesterday on mine and will do a turbo service later today.
I try to 3 turbo washes a season.

Extended amount of time is bad on turbo more than anything.
Turbo washes are very important.
I did oil change and all fuel filters yesterday on mine and will do a turbo service later today.
I try to 3 turbo washes a season.

How does one wash a turbo?

How does one wash a turbo?

Run engine to warm up to operating temp
While someone runs boat at full throttle inject Turbo wash solution.
50cc of solution injected with a syringe or spray bottle into side port of air intake over 10 second period
5-cc distilled water same procedure
....

repeate 2 more cycles solution then water

How does one wash a turbo?

With cars you have it done at the same place you get a shampoo for your engine.
I don't know it there are any Cartalk fans out there but they had a guy call in a while ago complaining about a problem that developed with his car after he had his engine shampooed, If you listen to the show you can guess how that went over:rotf2:

Run engine to warm up to operating temp
While someone runs boat at full throttle inject Turbo wash solution.
50cc of solution injected with a syringe or spray bottle into side port of air intake over 10 second period
5-cc distilled water same procedure
....

repeate 2 more cycles solution then water


Was wondering whether I should do it to my Jeep turbo diesel, I'll have to check it out. I do blast the thing out weekly but no wash.

Extended amount of time is bad on turbo more than anything.
Turbo washes are very important.
I did oil change and all fuel filters yesterday on mine and will do a turbo service later today.
I try to 3 turbo washes a season.

Not quite sure what you mean Ronnie when you say extended amount of time is bad on the turbo...........yes, if your refering to idling time?

Turbo washes are very important.........well......

Some things to think about. Turbos are meant to pump air, a turbocharger doesn't really start to get loaded up until the engine is around 80% load. If you had a pressure gauge on your intake manifold you would see this.

Turbo washes. Some engine and turbo engineers will discourage the use of turbo washing. The reason is you have to make certain the water solution is going in at a fine mist. If it is going in as droplets it may do more damage to the compressor fan than the cleaning function. Some engine designs actually inject finely ground walnut shells for cleaning, have never seen this myself.

For those of you wondering about turbo washing this is a system where water and solution is injected into the air intake side of the turbo (compressor) and then goes onto somewhat cleaning the fins on your aftercooler. This will not take off any carbon buildup on the gas turbine side cause by light load, idling.

This also relates to having a good air filter, less stuff to get on the compressor. For the most part boats are a very clean environment, compared to contruction sites. Sometimes a big culprit is belt dust from a poorly aligned belt.

I have CATS 3208 Turrbo. 315 HP. They seem to burn around 1 gal per mile each. I have a Garmin system, however the do not have a flowmeter for diesel. FloScan would cost me 1200 + installation. I would rather spend that money on fuel. lol. I appreciate all the advice and VAN you are right. That was funny.

90% of WOT is the norm for cruise speed, obviously you can't always do that depending on sea state. Diesels will idle all day, just make sure you bring them up to speed befor you shut them off to blow out the turbos.

I burn about a mile a gallon combined and run 2800-3100 depending on the situation. I try to Peg them at full throtle for a half minute or so right before I hit the no wake zone to blast em out. I'm a little Leary about squirting anything into my turbos.
Posted from my iPhone/Mobile device

I burn about a mile a gallon combined and run 2800-3100 depending on the situation. I try to Peg them at full throtle for a half minute or so right before I hit the no wake zone to blast em out. I'm a little Leary about squirting anything into my turbos.
Posted from my iPhone/Mobile device

I'm a little Leary about squirting anything into my turbos.

Recommended service per Yanmar