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Old 09-08-2019, 06:30 PM   #1
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05 Cummins 5.9 300 isb overheating?!

Ok so I took our holiday rambler to Yellowstone. In Kansas I started to get a check engine light that would come on for a few seconds then shut off. I also would note a loss of power with full throttle. So I had it checked at a diesel shop off the highway. I had an EGR that is 96% functional and over temp @ 230...we power washed the rads and got a ton of junk out but the light came back on. So we did it again after soaking with brake cleaner and purple power degreaser. The light still comes on for a few seconds then off or almost as soon as I get off the throttle. So I run the coach with an inch or 2 of throttle and in general can run 65mph @2100 rpm. If I go up a grade I keep the 2 inches of throttle and let the mph and rpm bleed down until were over the hill. Going down or flat I can usually go 70+ @2300rpm. The other issue is I have no water temp gauge. It's dead. SOOOO. I've also been running at night or cooler weather just as an extra precaution as well as with the cabin heat on...we're not boiling over or any water anywhere . Coolant is full. Can anyone tell me if there is a fan clutch on these engines? Other suggestions or things to check... can the lack of a working water gauge throw a code? I'm hoping it has a lot to do with the altitude too.

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Old 09-08-2019, 08:06 PM   #2
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I don't think it will show any codes. It could be the temperature sending unit on the engine that has failed for gauge. on mine if on steep hills i'll downshift to keep the RPMs up to close to 2500, this keeps the fan turning faster as well as the water pump. if you have a rear radiator yes there is a clutch on the fan. Altitude doesn't effect diesel engines like gas

99 Itasca, Sunflyer, ISB Cummins/Allison 36L
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Old 09-08-2019, 08:36 PM   #3
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Originally Posted by Skiddy View Post
I Altitude doesn't effect diesel engines like gas
I would only add to this good advice that altitude generally doesn't affect turbo diesels like non-turbo gas engines...
'04 Newmar Mountain Aire 4016
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Old 09-08-2019, 09:30 PM   #4
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It also seems to act worse when I stop for a break after 2-3 hrs driving. The last 2 times when the motor is cold soaked from not running it runs great in the morning nice strong until I pull over. Almost like the fan clutch is engaging but once stopping the heat gets it and it goes to crap.
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Old 09-09-2019, 11:29 AM   #5
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

Not a mechanic so can't help with that. Noticed you are kinda new on IRV2 and wanted to say hello!

Good luck, happy trails, and God bless!
Joe & Annette

2002 Monaco Windsor 40PBT, 2013 Honda CRV AWD
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Old 09-09-2019, 11:49 AM   #6
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IMO, you should really have it checked for codes since the CEL is coming on. It may or may not have codes stored, but you need to eliminate that possibility. I can't day definitively if your ISB has a fan clutch, from what I've read some do, some don't. Your issue may simply be electronic in that sensors are indicating an overheat condition or, you may have a fuel supply issue. Regardless, it would be wise to have a Cummins or independent expert on the ISB thoroughly go over the situation.
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Old 09-09-2019, 01:18 PM   #7
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IMO you should not even be driving it without a working temperature gauge. Best of luck finding your issue.
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Old 09-09-2019, 02:42 PM   #8
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First things first. Fix the temperature gauge and pull the code. You may be able to stop at an autoparts store (probably not NAPA) and ask them if they could pull it for you. I hear they do it for free, haven't tried it. A shop out in BFE wanted $15 to do it.

If you keep driving it and overheat it, the engine could blow a head gasket. If you are low on budget, a failure at that level is going to be a big pain point.
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Old 09-11-2019, 10:30 PM   #9
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Finally made it home! So it was a long 3 days of driving and what I've learned: if you think you need to check on something, dont wait... the first day we left Yellowstone I wanted to check to see how caked our rads were b/c we stayed at a camp with a 5 mile gravel road. Oil and dirt had made the first day miserable. We spent 2 hours at the car wash soaking them with "oil eater cleaner" (found @tractor supply) letting them sit for a few then power washing. It was like a totally different engine. I do think I have a charge air cooler leak though. While the CEL would still pop on, the most boost I saw was 20psi. Maybe a little more @night in the fog and rain. Next, I know I need to fix the temp gauge and took a risk of head damage but I needed to get home. Running the heat full blast with all the windows open isnt ideal but doing it at night sure helps, especially after a good rain. Denser air to compress for the turbo. I hope to tear into some things tomorrow. I'll post what I find... other than I'm pretty sure I dont have a fan clutch. Mine is direct drive.
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Old 09-12-2019, 09:30 PM   #10
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You might look into buying a scan gauge it will display your engine temp as well as many other features.
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Old 09-18-2019, 10:42 AM   #11
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I had a Cummins 5.9 that overheated also. It turned out that some mice/rats had built a nest in between the two radiators. I didn't know this Winnebago had 2 radiators, one in front of the other, but apparently it does. It cost about $5k to replace the radiators. I pressure washed, but the only thing I could see is water not going through and also noticed fan air was not coming through all sections of the radiators. You might check it out before you burn up the engine. Good luck.
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Old 09-18-2019, 12:16 PM   #12
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At that age, I would almost suggest pulling the rad for a good inspection and cleaning. You might well find its time to change the rad. While you are in there, change the water pump, belt tensioner, belt, and if the alternator is original, you might as well do that while you are at it. For a quick fix, try overfilling the surge tank with antifreeze. I found with mine, steep hills could cause the antifreeze to expose the sensor, even though it read full when parked. If too much gets in there, it will just spit it out.
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Old 09-18-2019, 02:59 PM   #13
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So here's what Cummins has to say.... the EGR valve, cooler and intake elbow are carbon'd up. And guess what! All not covered by my extended warranty. The good news is Cummins will replace them all and not reuse any bolt that holds any of it together.... for about $7k. So one of us is F'n crazy. They claim that in particular the simple elbow and rest are all non serviceable items and can only be replaced. They said absolutely zero about the radiators. BUT I know they still have oil and crap over most. What I'm working to come to terms with is letting someone else do the work. If this was the beginning of the summer.. no question I'd do the work myself. But with work being short and working 60+ hours a week I'm afraid I'll run out of time and be working in the snow. I think I still may be able to do a good Rad flush on the coach and they affirm that may CAC is NOT leaking... So other ideas pointer etc appreciated. Winniman... this was all my inital thoughts while I was on the road!

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cummins, heat, heating, overheating

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