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Old 09-19-2021, 06:10 PM   #1
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Cummins overheating

2005 Monaco diplomat with 400 horse Cummins;
It started overheating, having to downshift on hills.
Is this normal or should I start replacing/flushing antifreeze, it cools off in just a few minutes when I pull over and let it idle
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Old 09-19-2021, 06:18 PM   #2
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Most likely dirt and debri built up on the fins.
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Old 09-19-2021, 07:38 PM   #3
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Get some Simple Green Extreme Aircraft Aluminum cleaner and mix 4 to 1. use a pump up sprayer and wash the radiator from both directions.. Probably a lot of crud in there if its a rear radiator.. If that doesn't take care of it then its time for a coolant flush and refill. Thats what I went thru with our 04 HR.
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Old 09-26-2021, 12:58 PM   #4
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Monaco temp gauges are generally wrong, i had 2 monaco's both dash gauges were off by 10 to 15 degrees, I compared the dash gauge( temp) vs silverleaf that takes engine data from the cummins ecu. Monaco has separate coolant and oil pressure sending units, I have verified on an 99 isb and a 04 incident would always get the dash warning light on the 99 on uphill clips in 100 degree temps, dash gauge was showing 240, while cummins ecu was reporting 227, dash warning lights are fed from the Monaco sensors, not the cummins sensors.
JUST A FYI.
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Old 10-03-2021, 02:50 AM   #5
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i just had just crossed the rockies on our last trip 2006 Monaco diplomat cummins 400 and was having the check engine light an stop engine light come on. the gage never got in the red.got close, however when i returned home i decided to inspect the rear radiator from the inside side. wow i guess it had never been cleaned, it was thick with crude.i used the simple green air craft cleaner, it took several application but it increased air flow, looks like a yearly maintenance thing now
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Old 10-03-2021, 05:09 AM   #6
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https://www.homedepot.com/p/Web-19-o...IL19/301847065

I use this and the radiators are spotless.

I would highly suggest a thermostat replacement just for good measures. There was a change in their design around 2007 ish.
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Old 10-03-2021, 04:06 PM   #7
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I had this problem a few months ago. I cleaned the radiator and CAC with the aluminum cleaner and rinsed with a low pressure sprayer. There was some dirt that came out, but it still didn't solve the problem. It turned out my clutch fan had gone bad. Had to have that replaced, about $2500, and that fixed the overheating issue.
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Old 10-03-2021, 05:36 PM   #8
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Quote:
Originally Posted by Barnguy2 View Post
2005 Monaco diplomat with 400 horse Cummins;
It started overheating, having to downshift on hills.
Is this normal or should I start replacing/flushing antifreeze, it cools off in just a few minutes when I pull over and let it idle
Agree with all the Cleaning suggestions because I have had problems in the past. If it still overheats change the thermostat. Mine was sticking and it is not hard to change. I use Silverleaf on a PC and if I waited until my front gages told me it was overheating my engine would be ruined. I graph my temperature so I can see what is happening.
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Old 10-04-2021, 09:48 AM   #9
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Thanks for the update, i have a can. i use it on my home unit. i did the outside of the radiator an cac just recently with it but i didn't realize the back inside was so bad.the simple green air craft cleaner did a amazing job. i'll put this can to it today, just for a little extra clean and i'll order a new thermostat
Thanks for sharing
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Old 10-05-2021, 09:15 AM   #10
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[QUOTE=greystroke;5937343]Agree with all the Cleaning suggestions because I have had problems in the past. If it still overheats change the thermostat. Mine was sticking and it is not hard to change. I use Silverleaf on a PC and if I waited until my front gages told me it was overheating my engine would be ruined. I graph my temperature so I can see what is happening.[/QUOTE

I have a Aladdin system I was able to see the temperature the high was 239 not sure what is considered to high]
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Old 10-05-2021, 09:43 AM   #11
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[QUOTE=GMN;5939271]
Quote:
Originally Posted by greystroke View Post
Agree with all the Cleaning suggestions because I have had problems in the past. If it still overheats change the thermostat. Mine was sticking and it is not hard to change. I use Silverleaf on a PC and if I waited until my front gages told me it was overheating my engine would be ruined. I graph my temperature so I can see what is happening.[/QUOTE

I have a Aladdin system I was able to see the temperature the high was 239 not sure what is considered to high]
Don't know the specs on your engine but my ISB high warning light comes on at 213. My normal is 184. My front panel gage is in the normal area at 213. 239 sounds very high.
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