Target RPMs for Cummins 5.9BTA

[JohnBurreson]

Greetings forum folks,

I moved up from my beloved single Lehman 135SP 36GBCL last year to my new beautiful 42CL with twin Cummins 5.9B TA 330hp. I generally run at about 1250 rpm’s. I run up to WOT for about 10 minutes per month/10 hours. I just filled the tanks and took on. 284 gallons with 98 engine hours plus generator and furnace time. This is amazing fuel economy! Am I running at too low of RPMS?

Thanks for the advice for the neophyte! Be gentle…

 

[DavidM]

No I don't think you are running too slow at 1,250 rpm. I think I remember seeing Ski in NC post that 1,200 is fine. I would run up to higher rpms more often than once a month though. Maybe once a week at 2,400 to blow off any accumulated carbon then once a month at wot just to confirm no overheating and that it will reach rated rpms.

David

 

[Comodave]

If I remember on a 5.9 peak torque is around 1750 RPMs. It would be nice to be around that but your fuel economy will be worse. We have the 6CTAs in our current boat. We run the boat up on plane for about 20 minutes to start out the day and then slow down to a much slower speed. I want to warm up the engine for the days run.

 

[firehoser75]

John,
Having owned one of those engines, I concur with DavidM. I used to run (varying) between 1200 rpm and 1400 rpm achieving at fuel burn rate (averaged over several seasons and about 500-600 hours) of 2.0 gal/hr. I would change rpm every 20-30 minutes (between the 12-1400 rpm). Every 10 hours or so, I would run at 2300 for at about 10 minutes and every week or so I would run it up to WOT (2900 on my boat) for about 5 minutes to check things out. I discovered the beginning of a coolant leak that only showed up at WOT, and I carefully checked various engine temps using an IR thermometer.
Personally, I think these are great engines. However, stay on top of the aftercooler maintenance. For info on how to do that, and how often, see sbmar.com under Tony's Tips and on the Cummins forum there.

 

[murofrelwart]

In the last 3 years we have put over 800 hours on our twin Cummins 330 BTAs. 99% of that time was between 1100-1400 rpm with an estimated average of 1250 rpm. I do oil analysis at every change with good results. 2000 hours total time.


Early this spring we tried cruising at 1100 rpm due to higher fuel prices this year. After a month of that I decided a good minimum is 1200 rpm. 1100 rpm doesn't charge batteries well and oil pressure is lower. Right now we cruise at 1200 rpm if we don't care about speed but bump up to 1300-1400 if we'd like to go a bit faster.

 

[LouisG]

I must be some kind of fuel burning speed demon but I run mine mostly at 1700-1850. Nordic Tug 37.

 

[Nomad Willy]

John,
Having owned one of those engines, I concur with DavidM. I used to run (varying) between 1200 rpm and 1400 rpm achieving at fuel burn rate (averaged over several seasons and about 500-600 hours) of 2.0 gal/hr. I would change rpm every 20-30 minutes (between the 12-1400 rpm). Every 10 hours or so, I would run at 2300 for at about 10 minutes and every week or so I would run it up to WOT (2900 on my boat) for about 5 minutes to check things out. I discovered the beginning of a coolant leak that only showed up at WOT, and I carefully checked various engine temps using an IR thermometer.
Personally, I think these are great engines. However, stay on top of the aftercooler maintenance. For info on how to do that, and how often, see sbmar.com under Tony's Tips and on the Cummins forum there.

Between Firehoser and David these are wonderful words of experience and wisdom.
However it’s all predicated on being propped correctly. Two hundred or even 100rpm (not rpm’s as there’s no such thing as “rpm’s …. there’s only one minute involved) will make a significant difference in load. If you’re running at 1500rpm on an engine a huge to large difference in engine load my be happening if your’e over propped even 100-200rpm.
I notice very few here indicate their rpm at WOT and their rated rpm. Without this information not much can be learned nor is much said.

 

[Craig Christianson]

I have a Bayliner 3388 with twin cummins 4BT 3.9M 259 hp. Does anyone have good advice on replacing water pump impellors I have about 1,000 hrs on them.

 

[fryedaze]

I have a Bayliner 3388 with twin cummins 4BT 3.9M 259 hp. Does anyone have good advice on replacing water pump impellors I have about 1,000 hrs on them.

I can't find the Sherwood recommend replacement frequency but I change every two years. It works out to about 750 hrs. I see minor wear at 750 hrs. I run our 6BT at 1500 rpm. If you have old pumps consider a rebuild or new pumps. The seal can go and then they can get air bound if the pump isn't below the waterline.

 

[fryedaze]

I can't find the Sherwood recommend replacement frequency but I change every two years. It works out to about 750 hrs. I see minor wear at 750 hrs. I run our 6BT at 1500 rpm. If you have old pumps consider a rebuild or new pumps. The seal can go and then they can get air bound if the pump isn't below the waterline.

Sherwood recommendation.

 

[High Wire]

I have a Bayliner 3388 with twin cummins 4BT 3.9M 259 hp. Does anyone have good advice on replacing water pump impellors I have about 1,000 hrs on them.

Welcome aboard!
Agree with 2 years as a starting point with no other guidance. If you take them out and they still look like new, then extend to 3 years.

I just had one fail on our newish generator. The rubber impeller part became unbonded from the center metal hub at about 500 hours/3rd year. Fortunately we were eating in the salon when out of nowhere, the exhaust sound changed completely due to the loss of water. I shut the gen down immediately and no damage done. The impeller looked perfect except it spun freely on the center hub. Just saying there's more to impeller replacement interval than vane wear.

 

[firehoser75]

To the OP,
Eric (Nomad Willy) has raised an important point about being overpropped and therefore potentially overloading your engine. It is less of an issue when the engine is operated at lower rpm (like half throttle), but still an issue. The only way I know of to test for this on these older "mechanical" engines is testing at WOT. Rated RPM (by Cummins) for my engine, the Cummins 6BTA 330HP M3 version, is 2800 rpm WOT. However, the boat should be propped to achieve at least 2900-2950 rpm when wide open. After purchasing Pilitak, I had the prop adjusted (pitch removed) to achieve this. This testing is done with a clean bottom and the boat loaded as normally operated (eg. full water , fuel, supplies, etc.).
To Craig C:

As far as impellers go, I personally did not want to face an increased risk of impeller failure with all the resulting issues (like finding all the pieces, disassembly in a remote location, engine overheating with possible severe damage, etc.), so I changed the impeller annually (for the most part). A form of "insurance" for me!

For info and tips on both impeller changes and overpropping, check out sbmar.com under Tony's Tips and/or on his various forums. On that site there is a huge amount of very valuable, FREE, information and assistance from a diesel expert (Tony Athens). No affiliation, just found it useful.

PS. I recommend changing the Sherwood pump for the superior SMX pump that Tony makes and sells. Much easier impeller changes as well as being a better (more reliable) pump.

 

[bumpkin]

My mechanic, Cummins certified and I think, only works on Cummins, suggested that I run over 2,000 rpms everyday. He suggested to do this early in the day to take advantage of the hot engine burning fuel more efficiently for the rest of the trip. I asked how long to do this and he said 2 minutes should be enough. I have turbos not sure if that makes a difference.

Mike

 

[Comodave]

We have Cummins 6CTAs (450hp) in our boat. We usually cruise about 10 to 12 mph. But at the beginning of the day we run it up to about 2000 RPMs for about 15 minutes or so to heat the engine up. Then we slow down to around 1200RPM for cruise speed. Some people say run it up at the end of the day but I like to do it first to get the engine hot and then slow down and the engine will stay warm.

 

[OldDan1943]

bumkin, seems more reasonable to warm the engine at the dock. I want the engine to warm slowly, allowing for the metal and all gaskets to warm together aka become 'friends' again. Gives you the chance to inspect for leaks.
I was getting ready to exit from a bottom painting and hull valve servicing, tied to the dock, 10 mins, the engine stopped. Seems the yard had decided to shut off the RACOR and I didn't check. Why, I have to idea but, it happened at the dock and not while underway. As per racing the engine at the end of the day? I guess that all has to do with location and water under the keel. If you are in the ICW, NO! If you are in skinny water, you might want to think twice.

Edit: I have a Cummins QSB 5.9

 

[Comodave]

Diesel engines typically don’t get warmed up unless they are under load. Running them at the dock doesn’t really warm them up. Idling out of the marina or wherever is enough to get them ready to rock and roll.

 

[OldDan1943]

Diesel engines typically don’t get warmed up unless they are under load. Running them at the dock doesn’t really warm them up. Idling out of the marina or wherever is enough to get them ready to rock and roll.

Watch your temp gauge. You will no doubt see a temp increase at the dock while idling at the dock.

 

[firehoser75]

Diesel engines typically don’t get warmed up unless they are under load. Running them at the dock doesn’t really warm them up. Idling out of the marina or wherever is enough to get them ready to rock and roll.

From what i have learned from various well respected sources, I agree with Comodave!! Running at the dock before departing to "warm" the engine is not necessary and might only succeed in annoying other boaters docked nearby! The best warmup is under load at low rpm as in slowly exiting the marina or anchorage. Increase rpm to "cruising" rpm after the engine reaches 150 F +. At a marina, start up after disconnecting (electrical, etc.), check for proper operation (like cooling water flow etc.) cast off lines and get underway. Motor slowly out of marina at 1000 rpm or below until higher temps are reached. Takes only a very few minutes. This is the recommendation of Tony Athens a diesel guru from sbmar.com and formerly from BoatDiesel.

 

[OldDan1943]

From what i have learned from various well respected sources, I agree with Comodave!! Running at the dock before departing to "warm" the engine is not necessary and might only succeed in annoying other boaters docked nearby! The best warmup is under load at low rpm as in slowly exiting the marina or anchorage. Increase rpm to "cruising" rpm after the engine reaches 150 F +. At a marina, start up after disconnecting (electrical, etc.), check for proper operation (like cooling water flow etc.) cast off lines and get underway. Motor slowly out of marina at 1000 rpm or below until higher temps are reached. Takes only a very few minutes. This is the recommendation of Tony Athens a diesel guru from sbmar.com and formerly from BoatDiesel.

I never said it will get up to normal operating temp. I think my Cummins gets up to a steady 140F.
And yes, gives you time to undo everything and give the ER a final check.

 

[Comodave]

Watch your temp gauge. You will no doubt see a temp increase at the dock while idling at the dock.

Never said the temperature will not come up at all, obviously if it is running it will get warmer but it won’t come up to running temperatures. So running it at the dock to warm it up is just a waste of fuel.

 

[BruceK]

.... So running it at the dock to warm it up is just a waste of fuel.

and risks glazing the bores.

 

[North Baltic sea]

Hi, I have spoken with the technical customer service at the Cummins factory (US) and their view is to avoid idling for a maximum of 5 minutes.

Also they answered my question that my cummins qsb 5.9 can run fine rmp over 830rmp even 24/7, heats, carbon, glazing is not a problem, thanks commonrail.

NBs