Cummins 6BT 5.9 questions

[moparharn]

Looking at a displacement Trawler that has a single Cummins 6BT 5.9 from 1989 in it. 210 HP at 2600 rom the tag says. Last buyer backed away because of a few issues. The engine got hot when run over hull speed of 8 knots which occurred at 1150 rpm. The oil sender apparently has had issues and is reading low, however owner claims a mechanical gauge shows it is fine at what psi I do not know. also, the hour meter is not functioning. The owner says the hour meter and the oil gauge issues seemed to come on around the same time possibly after a new alternator was installed. I am thinking of installing a new impeller and a mechanical oil gauge to see if some of this improves.

1. Does 1150 rpm at 8 knots seem like the boat is over propped? It apparently pushes a big wave at much over that and this is when the motor got hot.

2. Is installing a mechanical gauge as simple as removing the sender and threading a mechanical one with a dial right on the engine?

3. Can the cummins gauge cluster be sent in to be reworked?

4. The last purchaser walked, am I the next fool in line?

Thanks for any thoughts you might share.
Bill

 

[Pau Hana]

Looking at a displacement Trawler that has a single Cummins 6BT 5.9 from 1989 in it. 210 HP at 2600 rom the tag says. Last buyer backed away because of a few issues. The engine got hot when run over hull speed of 8 knots which occurred at 1150 rpm. The oil sender apparently has had issues and is reading low, however owner claims a mechanical gauge shows it is fine at what psi I do not know. also, the hour meter is not functioning. The owner says the hour meter and the oil gauge issues seemed to come on around the same time possibly after a new alternator was installed. I am thinking of installing a new impeller and a mechanical oil gauge to see if some of this improves.

1. Does 1150 rpm at 8 knots seem like the boat is over propped? It apparently pushes a big wave at much over that and this is when the motor got hot.

2. Is installing a mechanical gauge as simple as removing the sender and threading a mechanical one with a dial right on the engine?

3. Can the cummins gauge cluster be sent in to be reworked?

4. The last purchaser walked, am I the next fool in line?

Thanks for any thoughts you might share.
Bill

Some info for your readimg pleasure:

https://www.sbmar.com/engine-info/cummins-6bta-specifications/

Next, email Tony Athens at Seaboard Marine (SBMAR) with specific questions.

tony@sbmar.com

 

[High Wire]

1- depends on the boat weight but it sure sounds over propped or the tach or speed is very wrong

 

[Ken E.]

To get 8 kts at only slightly above idle, something is haywire...faulty tach or way overpropped. I have these engines.

 

[O C Diver]

While I would guess that the boat is over propped, an engine over heating can be do to numerous things. We're talking about a 30 year old motor. While it could be on the raw water side, it could also be on the freshwater side or a flow reduction in either the heat exchanger or exhaust elbow. If the boat has always cruised at 1150 RPM, there could be other issues also. In a perfect world, that engine should be cruising between 1,800 and 2,400 RPM.

Ted

 

[HopCar]

I had a 6BT5.9 on Possum. Excellent engine. I bought a whole new gauge panel from Seaboard Marine. I’m sure they could rebuild yours.
Like Peter said, give them a call about the other issues you’re having.

As I recall I was turning a four blade 19” square prop and the engine turned up to just about 2700 rpm. Possum was smaller and semi displacement.

 

[Ski in NC]

All those issues sound minor. Also do doubt you are doing 8kts at 1150. Either over propped or inac tach.

 

[fryedaze]

I have same 1989 210 6BT5.9. 42 foot 30000 lb trawler. 8 knots at 1600 rpm. Boats propped to run 2600 WOT. That year has no margin in the cooling. If the hx are not clean they can't tolerate high loads. SBMAR has suggestion on improving cooling.

 

[moparharn]

I thank each of you for your posts. Very insightful and helpful. I likely will need an engine survey, or at a minimum have a Cummins tech come and review the engine. Does anyone know where I tap into the oil pressure for a mechanical gauge on that engine? Bill

 

[firehoser75]

Bill,
Follow the advise to contact Tony Athens at Seaboard Marine. He is the guru when it comes to marine diesels, particularly Cummins (which are great engines generally speaking). Take lots of high quality, well lighted photos both up close and at a distance so he can "see" what you are seeing. He does sell product, but he also is very helpful with info and suggestions.
Cooling is critical, but usually very solvable. This engine should be propped to hit 105% of WOT rating with the boat fully loaded (after the cooling issue is solved).
Good luck.

 

[Beaverlake]

And DO get an engine survey. A good one. It is *not* an expense, it is an investment.

 

[Ski in NC]

I thank each of you for your posts. Very insightful and helpful. I likely will need an engine survey, or at a minimum have a Cummins tech come and review the engine. Does anyone know where I tap into the oil pressure for a mechanical gauge on that engine? Bill

Top of oil filter housing, right above oil filter. There is a 1/8"NPT plug there. Also on left side of engine block, a couple plugs there. Some have block of metal with oil and fuel taps also on the left side, right behind sea water pump.

A handy help is a grease gun hose with gauge coupled to one end. Both ends are 1/8NPT and the hose lets you hook it up where gauge probably would not fit.

 

[kapnd]

Somethings rotten in Denmark!
Propeller and/or gear ratio is wrong, barring other problems like a bad tach reading.
You want to find your 8 knots in the 16-1800 rpm range.
Post specifics for some help here, or work with a reputable prop shop to get this sorted out.
You’ll need To know the boats weight and gear ratio For starters.

 

[bayview]

since installing a new oil pressure sender is as easy as hooking up a mechanical gauge i question the owners story.

 

[moparharn]

I must say that I am really encouraged by the advice and help offered on this forum. A heartfelt thank you to those who bothered to post. The purchase of this boat is likely not going to happen as the owner and I are too far apart on the value of the boat given my perceived needs. I will let this post end here. I am going to start a new post on an issue that I have seen and would like some advice should I see it again. It is in regards to ballasting. Thank you again, Bill

 

[C lectric]

I realize you want to end but I will add a bit. It is possible the original owner over propped deliberately to keep revs down thinking of fuel use and noise reduction. There is an argument both ways.

However, it that is what he was thinking then he went to far.