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Old 07-26-2010, 07:11 AM   #1
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Onan HDKAK High Coolant Temp Diagnostic

In February this year we purchased a 2004 Travel Supreme 40DS04. The coach was low mileage (27K on ISL and 359 on HDKAK). Since purchasing in February, we have put slightly more than 8,000 miles on the odometer and 150 hours on the genset. Everything has performed flawlessly until a few weeks ago, as we were coming to the end of a trip through the southwest. Leaving California at Blythe and traveling to Phoenix, the genset stopped suddenly with a diagnostic fault 33, high coolant temperature. It has continued to stop, intermittently, with the same diagnostic, over the past few weeks. It will drop out when the ambient temperature is in the low to mid 90's and with only one rooftop air running.
I have done the following:
1. checked to insure there is no airflow issue through the genset housing and across the radiator/engine. I can hold my hand in the discharge duct near the tailpipe and the temp is not excessive.
2. Drained the genset coolant.
3. Added radiator flush/water and ran for 20 minutes.
4. Drained and flushed the "flush" with water, ran for 10 minutes.
5. Refilled with new antifreeze, insuring that no air remains in system, through several warm up/cool down cycles to purge air in the coolant lines. Removing the radiator cap while cold has coolant to the top of the fill tube.
None of this has solved the problem. The genset starts and runs as expected, until the ambient temp reaches the mid 90's, with humidity in the 50% range (not comfortable) and will stop with just one rooftop running.

Have others experienced this problem and, if so, any suggestions? I suspect the temp sending unit may have a problem, but the diagnostic never indicates the temp sender is the issue, just high coolant temp...

Thanks for any help.
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Old 07-26-2010, 09:06 AM   #2
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Sounds as though there may be insufficient air flow over the genset radiator. Have you checked the air intake at the bottom front of the generator to make sure it is not obstructed? I've heard of road debris getting sucked up in there.
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Old 07-27-2010, 09:52 AM   #3
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Quote:
Originally Posted by RV Roamer [Gary] View Post
Sounds as though there may be insufficient air flow over the genset radiator. Have you checked the air intake at the bottom front of the generator to make sure it is not obstructed? I've heard of road debris getting sucked up in there.
This was the first thing I checked. I can see through the wire screen which is there to stop debris (such as wal-mart bags, trash, etc) from entering the cooling air flow. Behind it is the squirrel cage fan which pushes air through the genset and radiator and out the exhaust cooling port. There are no obstructions.

Based on all I have done, I believe this is related to some change in the values provided to the control system from the temperature sender. However, the genset includes diagnostics for a failed temperature sender (code 24) and that is not the diagnostic I am getting. I am getting a coolant overtemp (code 33). I was hoping their might be someone else on the site who had experience with this problem. A genset that quits when the ambient temp reaches mid - 90's is not a good thing...

I am still researching the internet for solutions. If I don't find anything, i may go ahead and replace the temp sending unit, but that's a pain as the top cover on the units will have to be removed.

Thanks for the suggestion....
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Old 07-27-2010, 04:56 PM   #4
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Check to see if you have air flow on the exhaust side.
If you don't, your fan belt is the issue. Maybe it is loose
so it catches intermittently or it is kaput.
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Old 07-27-2010, 05:43 PM   #5
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I had a similar issue after a coolant change had been done by "professionals" and found there was indeed still air in the sytem. I pulled the filler neck upward out of the genny enclosure and ran it quite awhile "burping" it and additing coolant as required. Sometimes when I shut it down, it would burp more air out and I would go through the routine again.
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Old 07-27-2010, 09:54 PM   #6
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We had the same problem about 2 months ago. Our generator worked fine until we got into higher ambient temperatures. Our expensive lesson goes as follows. We had the gen radiator cleaned and repaired (it was about 30 percent blocked). Didn't fix it. We replaced the temp sensor. Didn't fix it. We replaced the water pump. Didn't fix it. We replaced the temperature regulating valve (thermostat). Didn't fix it. We applied steam pressure to clean the internal cooling passages in the engine block. Didn't fix it. We flushed with Prestone super flush. Didn't fix it.
We found a flush that had a fairly strong hydrochloric acid content. Didn't fix it.

We finally found Fleetguard Restore Plus and flushed with that. 3 times we flushed. That fixed the problem. You wouldn't believe how dirty the water was and the crap that came out when we flushed with the Fleetguard.

Long story short, we bought our motorhome, a 2005 Itasca Meridian, this past March. After delving into the guts of the generator it became apparent that the generator had recieved little to no maintenance on the cooling system. It appeared the cooling system had been topped of with tap water. As long as the external temps were less than 90 degrees it ran fine. Over 90, it would quit running with a secondary code of 33.

We may not have needed to replace all that we did but I have more confidence in our generator now. Flushing with the Fleetguard is what did the trick. Fleetguard should be available at any Cummins dealer.
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Old 07-28-2010, 06:35 AM   #7
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Quote:
Originally Posted by fputnam View Post
We had the same problem about 2 months ago. Our generator worked fine until we got into higher ambient temperatures. Our expensive lesson goes as follows. We had the gen radiator cleaned and repaired (it was about 30 percent blocked). Didn't fix it. We replaced the temp sensor. Didn't fix it. We replaced the water pump. Didn't fix it. We replaced the temperature regulating valve (thermostat). Didn't fix it. We applied steam pressure to clean the internal cooling passages in the engine block. Didn't fix it. We flushed with Prestone super flush. Didn't fix it.
We found a flush that had a fairly strong hydrochloric acid content. Didn't fix it.

We finally found Fleetguard Restore Plus and flushed with that. 3 times we flushed. That fixed the problem. You wouldn't believe how dirty the water was and the crap that came out when we flushed with the Fleetguard.

Long story short, we bought our motorhome, a 2005 Itasca Meridian, this past March. After delving into the guts of the generator it became apparent that the generator had recieved little to no maintenance on the cooling system. It appeared the cooling system had been topped of with tap water. As long as the external temps were less than 90 degrees it ran fine. Over 90, it would quit running with a secondary code of 33.

We may not have needed to replace all that we did but I have more confidence in our generator now. Flushing with the Fleetguard is what did the trick. Fleetguard should be available at any Cummins dealer.
I'll try and find some Restore plus flush treatment. Like you, I used Prestone, because it is everywhere. We are traveling the next two weeks and I should be able to pick some up at a cummins facility. Hope I have the same success as you...

To everyone else who has replied with helpful suggestions, thank you.
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