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Onan 12.5 Generator High Temp Fualt


Mike Wahl
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We have a 2001 Signature with a Onan 12.5  Model HDCAB11506A generator.  Last year I had posted we had an issue with over temperature fault.  Last year I cleaned the radiator fins and tighten the fan belt and the problem went away.  We put over 125 hours on the generator after this work was done.  The other day we had the generator running with all 3 roof top AC one and the generator shut down for over temp. 

Last evening I pulled the top off of the Generator to check the belt and the tension looks fine.  From what I can see the belt looks like it is in good condition, however it not easy to see.  I can not find any record of the belt being replaced in the documentation we got with the coach.  The generator has about 1900 hours on it.

I also checked that the radiator didn't have anything blocking it and the coolant recovery tank has the proper level in it.

When it shut down I opened the side panel and it was definitely hot.  This then rules out a faulty water temperature sending unit in my mind. 

I started the unit and the fan turns and it doesn't sound like the belt is slipping.  I put the cover back on and I can feel air being push out he back end, however after a 1/2 hour or so the housing in the back area was getting hot to the touch.  From what I can find the shut down temp is 230°F.  The max running temp should be 104°F over the ambient temp.  It was 70° last night and I had check the hose temp at around 185°F.  

Just wondering if anyone else has seen this issue.  I'm trying to decide my next steps.  I'm thinking about replacing the belt.  It could be old and glazed and not driving properly. Do I replace the belt only or do I do the thermostat and water pump while I'm at it.

 

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I'd say it depends how much you hate crawling under and opening the rear generator housing again. But since you have overheating issue, it might be a good idea anyway. Maybe I am lucky but with only few hours left to be at 4K, I only replaced the belt in that area but I don't consider it a huge job even if I had to do it in the field. Just as long as we make it out of this Oklahoma heat tomorrow, would not want to do it here today...

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6 hours ago, Mike Wahl said:

 

I also checked that the radiator didn't have anything blocking it and the coolant recovery tank has the proper level in it.

 

 

Don't know if your early 2000 model gen has the same design as mine, but, did you pull the upper rad hose out and make sure there was coolant right up to the cap?

The recovery tank on these Onans can show a level even if there is no fluid going back and forth.

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11 hours ago, 96 EVO said:

Don't know if your early 2000 model gen has the same design as mine, but, did you pull the upper rad hose out and make sure there was coolant right up to the cap?

The recovery tank on these Onans can show a level even if there is no fluid going back and forth.

Ben

I didn't do that.  That is an easy check that I didn't think of.  From my understanding the early models have that same issue where they can get an air trapped in the line.

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  • 3 weeks later...

I wanted to give an update on my over-temperature issue.  After I removed the top cover and was able to get in and get a better look at the belt, I found that the alternator pulley was not running parallel with the water pump and crankshaft pulleys.  I proceeded to remove the back cover and found that the nut that fastens the bottom of the alternator to the block missing and the adjustment bracket on the top that allows for belt tension cracked.  This allowed the alternator to pivot around the look bottom bolt, putting the pulleys out of alignment but the belt stayed tight.  This misalignment caused the belt to wear on the sides as shown in the photo and eventually cause it have limited contact with the pulleys.  

I went to the Cummins site to purchase a new belt and bracket.  The was bracket was $27.00 and like other supply chain issue will ship sometime in the future.  I tig welded the cracked one back together till the new one arrives.  I priced out the belt from Cummins and it was $142.   I had the original belt and part number by Bando.  I did a little internet searching and found the belt by Bando from Diesel Parts Direct for $12.76.  I purchased 2 of them, so I had a spare,  for less than $50 with shipping.  When the package arrived with the new belts, the packaging called it an Isuzu water pump belt.   The Bando Part number is 8972249991 for Onan Model HDCAB11506A 12.5KW Generator

Last week I finished reassembling and test ran the generator for about an hour with all three AC's running and had no issues.  It worked fine over the weekend, however it was in the low 70's during the day here in Wisconsin so we didn't run the AC.   Hope this information can help someone in the future.

 

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