Cummins 6BT Idle Speeds

[Matchmaker]

We are running a pair of Cummins 6BTs on a 1987 41’ Symbol Sundeck trawler. We are new to the boat and unsure as to how low I can st the idle. Currently set at 1000 rpms and I find it a bit fast when maneuvering through the marina. We have oversized props but I don’t know the pitch. Any advice?

 

[Comodave]

1,000 is too high. I would rather have them around 750 give or take, maybe a bit less even. At 1K you may be slamming them into gear and eventually doing damage to the transmissions. Also at idle you must be moving fast enough to leave a fairly big wake. My boat idles in the 650 to 700 range with twin 6CTAs. It is almost to fast and the wake is nearly too big. I would ensure that your boat will reach the max recommended RPM, actually 50 more, so you aren’t lugging the engines. Check out Tony Athens website, sbmar.com, for info about reaching max recommended RPM. He is very adamant that you reach max recommended +50. He is the Cummins guru so I listen to him.

 

[bshanafelt]

600 is normal low idle

 

[HopCar]

I had my 6BT5.9 set to idle at 700 rpm.

 

[LarryM]

From the Cummins 6BT Marine Engine Performance Data Sheet:

Engine Model..................................................6BT5.9-M (CPL2891)
Rating Type....................................................Intermittent
Rated Engine Power ........................................kW [HP] 157 [210]
Rated Engine Speed.........................................RPM 2600
Rated HP Production Tolerance..........................% ±5
Rated Engine Torque .......................................N•m [ft/lb] 603 [444]
Peak Engine Torque @ 1700 RPM.......................N•m [ft/lb] 719 [530]
Brake Mean Effective Pressure ..........................kPa [PSI] 1229 [178]
Minimum Idle Speed Setting..............................RPM 700
Normal Idle Speed Variation .............................RPM ±50
High Idle Speed Range - Minimum......................RPM 2808
High Idle Speed Range - Maximum.....................RPM 2912

These specs are for the CPL2891 configuration but all 4 of the 6BT models indicate the same Idle Speeds.

 

[Comodave]

Yes, I think 1,000 is way too high. I would set it around 700. Also check the WOT RPMs and make sure you can turn that.

 

[Matchmaker]

Thank you all for your advice.

Thank you all for your advice and no sarcastic comments!

 

[Comodave]

Thank you all for your advice and no sarcastic comments!

I am capable of making sarcastic remarks…

 

[twistedtree]

BTW, there is a distinct possibility that the idle is set high for a reason, like stalling of the engine when shifting into gear. Hopefully not, but go in prepared to find more to the problem.

 

[HopCar]

No sarcastic comments! We’re slipping guys.

1000 rpm! What’s your hurry?

Sounds like you found a loop hole to get through idle zones quicker.

 

[Arc]

How or who set the idle that high? Many gear manufacturers will state not to exceed 900 when shifting

 

[CharlieO.]

Could it be stuck in a high idle mode?