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Old 05-23-2011, 06:16 PM   #1
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Overheating 275 Cummins Diesel

I have a 2000 Fleetwood Discovery 37G with a 275 Cummins Diesel. I normally drive at 60 to 62 mph and at times when the outside temp is around 80 or above and I am putting a load on the engine by going up a grade I will get an overheat light and I can back off on the speed which brings the temp back into the normal range and the overheat light goes off. The fluid levels are fine as I just had the RV serviced. My questions are these: Is my 275 Cummins too small and this is normal? Would a complete flushing of the cooling system be a solution? Would installing an additional fan in the engine compartment be a solution? Any suggestions?

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Old 05-23-2011, 06:36 PM   #2
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A flush and inpsection is always a good start...You may be lugging the engine under a load. Cummins love to work hard but keep the rpms up to keep the fan spinning good. Try a lower gear to get the RPM's 200-300 higher. If you have overdrive turn it off while climbing as well as the AC. The thermostat may be getting stiff also.

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Old 05-23-2011, 06:51 PM   #3
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It's most likely that your rear radiator is dirty and needs cleaning. There have been lots of posts on this forum on this topic. The 'slobber' tube (engine breather) on earlier coaches is mounted before the rear radiator and throws oily mist into the radiator. Dirt then gunks it all up.

Clean the radiator before other work. Don't use a pressure washer - will bend the fins.
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Old 05-23-2011, 08:39 PM   #4
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Originally Posted by Pusherman View Post
It's most likely that your rear radiator is dirty and needs cleaning. There have been lots of posts on this forum on this topic. The 'slobber' tube (engine breather) on earlier coaches is mounted before the rear radiator and throws oily mist into the radiator. Dirt then gunks it all up.

Clean the radiator before other work. Don't use a pressure washer - will bend the fins.
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Old 05-23-2011, 09:20 PM   #5
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Pusherman and Acker1 are spot on. The slobber tube tends to gunk up the radiator with oil which in turn attracts dirt.
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Old 05-23-2011, 09:33 PM   #6
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Mechanic once told me the full mud flap sends a lot of the road dust into the radiator.I extended the slobber tube behind the radiator.Also downshift to keep the rpms over 2000 helps.
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Old 05-24-2011, 02:42 AM   #7
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The radiator is a likely culprit, but the thermostats on this vintage of ISB failed with some degree of regularity as well.

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Old 05-24-2011, 03:35 AM   #8
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Clean your radiator good, spray it down with simple green, let it sit for a bit and wash out with hose. Be careful not to bend the fins in the radiator(no pressure washer). Hint the dirt and gunk will be on the front of the radiator you will need to lift the bed to get at it continue until it is clean. As other posters have said you need to keep Cumming humming, rpm's up around 1700 or better it will make the motor happier, and you may find your fuel mileage will go up. If you have the engine book that came with your coach take a look at it I think you will find your engine builds it's bst power between 17-1900 rpm where the torque and horsepower curve meet.
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Old 05-24-2011, 04:37 AM   #9
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In addition to thoroughly cleaning your radiator and CAC make sure you extend your "slobber tube"! Here's several remedies which have been used

Slobber/Breather Tube Extensions
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Old 05-24-2011, 10:15 PM   #10
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I have to agree with everything that's been posted here. I too, have a 2000 Discovery and I went through the overheating thing last month when I drove it across country coming home from South Carolina to Reno. I put a post on here and got the same advice that you are getting. I took mine to Cummins. Had them change oil, lube, change oil in the generator, change some hoses and completely remove & clean the rear radiator. Bingo...no more overheating! It only cost me $1700.00. I'm sure you can beat that price, but I'm also sure that the radiator and the slobber tube is your culprit.
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Old 06-07-2011, 09:50 PM   #11
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Had a '99 Discovery with same ISB engine. Total washdown of CAC the thing that looks like a radiator, but it is not and it is what you see from the rear of the coach. Slobber tube mods can be done for less than $5 and less than an hour DIY. The Simple Green washdown may take several applications---stay at it until you only see clear water. BTW, the 275 ISB is a great match for your coach relative to weight, wheel base, etc. When you get over 40,000 miles you should see an increase in MPG-we got 11 and a half plus and we towed a Blazer 4 down and did the mountains of PA,VA and TN with no sweat. Note how many '98., '99 '00 and some '01s Discoveries you see around. They are a great coach with all the guts most of us will ever need. To put your mind at ease read the Cummins manual re warranty, that will give you a hint what you can expect, Ken Roberts....

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