Cummins 5.9 QSB 380 hp Temperature Alarm

[James Rowe]

I was sea trialing a boat we are considering purchasing and while running a short distance at 3000 RPM the overheat alarm went off and the gauge is reading 183 degrees. I am trying to understand what temperature the alarm should go off. It seems like 183 is higher than what I would expect. I would expect about 176 to 178. Question is what temperature is the alarm supposed to go off? 183 degrees is not that much over what I thought would be the normal operating temperature which I thought was 176 to 178. Thanks in advance for the help

Topic

[Tony Athens]

IMT 141 F–If this was at some lower RPM,  like cruise,  then this was your alarm.

 

100% aftercoolers need proper servicing.

 

 

[James Rowe]

Tony, 

    Thanks again for your responses. I started going through all of the pictures we took of the SmartCraft gauges during the sea trial and noticed we did have pictures of the intake temperatures on both engines. Not necessarily when the alarm went off, but at high RPMs. I am attaching all of the photos for your sharp eyes! 

[Tony Athens]

under 180F would be normal  coolant temps

under 110 F would be normal IMT temps  

 

The aftercoolers are most important as this stage.

 

 Plus, pictures of the engine installation  from all around would be a very advantageous for you–My eyes  miss nothing if the pics are good.  Download the attached example.  

[James Rowe]

Thanks again

Thank you again. Since I am in the process of buying the boat, I have asked the owner to have both aftercoolers. Fuel coolers, transmission coolers and heat exchangers taken apart, serviced, pressure tested and reinstalled. We will then do another sea trial to make sure the alar, doesn’t go off again. I would think if they perform all of these services using the Seaboard Marine process, it should correct any issues and the alarm will no longer sound. What temp should these engines run at about 2450 RPMs in a Tiara 3600 Open? 

[Tony Athens]

IMT = Intake manifold temperature

My guess would be that what alarmed– Maybe a never proper serviced aftercooler , or in need of service, or worse?

History– You are dealing with old an mercury vessel view and it may not show history– The history is in the ECM but you need proper instruments to read it.

IMO,   Mercury  Smart Crap instruments ( especially from this era) are barely a cut above of  “Driving Blind” as they came from their outboard engine division.

The ECM on all the the Q engines have a vast about of data at you finger tips once to go back to its parent language, SAE J1939, and can read it.

[James Rowe]

Gauges

Thanks Tony, They are the Mercury Smartcraft Gauges. I am attaching a picture of each of the gauges before it went off. I am not sure if it was the Temperature Alarm, and since it isn’t my boat “yet”, don’t know how to get into see the alarm history. Can you tell me how to check to see which alarm went off? What is the IMT alarm? 

[Tony Athens]

what exact type of displays do you have?

Your factory coolant alarm set point is closer to 200F 

Are you sure it was a coolant alarm and not a IMT alarm or ??

Got a pic of the display?  Look at your history.

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