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Old 05-13-2015, 08:21 PM   #1
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Starboard Cummins 6BTA 5.9 250HP running too warm.

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Took the boat for sea trial yesterday and the starboard engine was running about 10 degrees warmer (200 degrees) than the port at 1800 RPM. All thru the 1 hour trial the starboard engine ran higher than port. Temp taken with gun, strainers clean, impeller fine. The gauge did flicker a bit and I suspected a thermo. I ran up to Portland and bought 2 new thermostats/gaskets today. The thermo change is a REAL son of a gun being the starboard engine in a tight area with many parts having to be removed. So I go ahead and get started and notice someone has been in there before and likely changed the stat. The port engine is factory untouched in that same area. Soooo, I am now second guessing taking everything apart and changing it.
Thanks,
Rob
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Old 05-13-2015, 10:52 PM   #2
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What does the engine temp do light load vs heavy load? A thermostat usually has about a 10F controlling range so at light load 190 and heavy load 200 means it is controlling there. If light load 170 and heavy load 200 sounds like fouled coolers or sea water restriction.
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Old 05-14-2015, 12:31 AM   #3
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Keep in mind that one transmission is rotating opposite than the other, so that corresponding engine will be working harder, so running hotter and using more fuel. As long as the two trannys are working opposite each other, the engines could be tuned identically but will not have the same operating characteristics
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Old 05-14-2015, 01:00 AM   #4
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Well the problem with not taking it all apart is that you can not trust that the last person who went in there knew what they where doing. Check the last place that was worked on ( in this case the thermostat) verify that it is correct and then go from there. And while it is a simple thing to change you would be surprised how many times it gets screwed up.
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Old 05-14-2015, 06:55 AM   #5
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10deg F is probably beyond the accuracy range for electric gauges.

Try swopping the gauge in the dash and see what the readings become.
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Old 05-14-2015, 09:16 AM   #6
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flickering is a clue. you may have a loose connection or a bad sender. If one engine is hooked up to a water heater that will make a small difference.
Typical reasons for cooling problems with cummins is pieces of old impellers partially clogging the next thing in line such as tranny cooler, or pieces of old zincs doing the same in the heat exchanger or after cooler.
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Old 05-14-2015, 10:27 AM   #7
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Can you explain this?

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Originally Posted by Patemey View Post
Keep in mind that one transmission is rotating opposite than the other, so that corresponding engine will be working harder, so running hotter and using more fuel. As long as the two trannys are working opposite each other, the engines could be tuned identically but will not have the same operating characteristics
This is the first time I've heard this, can you explain how this works?
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Old 05-14-2015, 10:46 AM   #8
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Heat gun

Since you mentioned you are using a heat gun. Try progressively measuring the temps from the sea strainer at each component to the thermostat housing, then check exhaust manifold, and exhaust shower or riser. No turbo on the 250 right. If turboed the intercooler and turbo housing as well. Looking for the difference will give you a clew. Check the inlet side of the transmission cooler and or engine cooler for impeller pieces. I've actually had impeller pieces shrapnel and end up in the inlet side of the raw water pump. 10 deg is not a lot but it could be differences in valve adjustment, injection problems, or timing.
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Old 05-14-2015, 11:05 AM   #9
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Just finished changing the stat, what was in there was not a cummins stat so hopefully that was it.....maybe, wishfully
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Old 05-14-2015, 12:46 PM   #10
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No turbo on the 250 right.
NA versions of this engine are 115hp. The displacement of this engine is very similar to the Ford Lehman. So it is turbo. The "B" in the title is the model. The "T" is turbo. The "A" is after cooled. Just for future reference on Cummins nomenclature...
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Old 05-14-2015, 04:44 PM   #11
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I went through this on my 5.9. Let us know if your new thermostat fixed the problem.
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Old 05-14-2015, 10:11 PM   #12
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Sea trial today was good, did not get warm at all. Leaving in morning for Portland Maine. 7 hour cruise or so, I'll know soon enough if all is well or
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Old 05-14-2015, 10:15 PM   #13
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NA versions of this engine are 115hp. The displacement of this engine is very similar to the Ford Lehman. So it is turbo. The "B" in the title is the model. The "T" is turbo. The "A" is after cooled. Just for future reference on Cummins nomenclature...

Great info, thanks
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Old 05-14-2015, 10:18 PM   #14
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Quote:
Originally Posted by Scary View Post
Since you mentioned you are using a heat gun. Try progressively measuring the temps from the sea strainer at each component to the thermostat housing, then check exhaust manifold, and exhaust shower or riser. No turbo on the 250 right. If turboed the intercooler and turbo housing as well. Looking for the difference will give you a clew. Check the inlet side of the transmission cooler and or engine cooler for impeller pieces. I've actually had impeller pieces shrapnel and end up in the inlet side of the raw water pump. 10 deg is not a lot but it could be differences in valve adjustment, injection problems, or timing.
Great advise but my heat gun went away when the mechanic left, almost went and bought one but I have 2 back home.
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Old 05-14-2015, 10:20 PM   #15
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Originally Posted by bayview View Post
flickering is a clue. you may have a loose connection or a bad sender. If one engine is hooked up to a water heater that will make a small difference.
Typical reasons for cooling problems with cummins is pieces of old impellers partially clogging the next thing in line such as tranny cooler, or pieces of old zincs doing the same in the heat exchanger or after cooler.
Thanks, good info
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Old 05-14-2015, 10:22 PM   #16
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Quote:
Originally Posted by FF View Post
10deg F is probably beyond the accuracy range for electric gauges.

Try swopping the gauge in the dash and see what the readings become.
Heat gun gave these readings not the guages but that is a good idea
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