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Old 07-14-2021, 04:44 PM   #1
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Cummins 8.9 gets hot looking at a hill?? :-(

Got a new to me 41' pulling a Jeep Wrangler and the Coach gets hot looking at a hill. This happened coming to San Diego from Las Vegas pulling the 1st big hill. Chocked it up to Temp being 115*. Did it a second time pulling the the grade into Flagstaff from Phx at 97* temp? I am sure this should rig should be able to pull this with the small load we are pulling. Am I full of it? Any and all comment, Suggestions, I would be thankful for.

Ted
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Old 07-14-2021, 04:47 PM   #2
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Sorry if Duplicate. Charleston getting hot on hill.

09, 41', 8.9 Cummings new to me. Getting hot pulling a jeep wrangler toad on hills? Any comments from owners. any and all apricated.

thx TEd
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Old 07-14-2021, 05:22 PM   #3
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I have heard that some pushers of that era are prone to having road debris plug the radiator between the charge air cooler and radiator. Check with a flashlight.
Some of those have a kit that extends the crankcase vent tube to the back of the coach so oily residue doesn't get on the radiator, which makes it sticky allowing dirt to accumulate.
Just a guess, of course. That coach shouldn't have a problem with hills.
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Old 07-14-2021, 05:26 PM   #4
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Originally Posted by n1acguy View Post
I have heard that some pushers of that era are prone to having road debris plug the radiator between the charge air cooler and radiator. Check with a flashlight.
Some of those have a kit that extends the crankcase vent tube to the back of the coach so oily residue doesn't get on the radiator, which makes it sticky allowing dirt to accumulate.
Just a guess, of course. That coach shouldn't have a problem with hills.
Thx for the Reply, We soaked the Rad from the inside with Simple Green and sprayed as many recommend, 1/2 way through the trip, still got hot. Also did not seem very dirty?

thx Ted
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Old 07-14-2021, 05:55 PM   #5
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Where are your Engine RPMs sitting? I don't know as much about the Cummins, but on my Duramax, I had similar issues until I started using manual mode and keeping the engine RPM above around 2300 going up hills. Went to manual mode on the trans, shifted down, kept RPM btw 2300 and 2800 and no more getting hot. That LBZ diesel would pull the grade just fine in high gear but it wouldn't shed the heat properly.
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Old 07-14-2021, 06:19 PM   #6
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I donít own a MH


I did Google it and got tons of infoÖ. Assuming you may not have.
I searched 8.9 Cummins rear engine over heating.
I bet the answer is there
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Old 07-14-2021, 08:26 PM   #7
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Originally Posted by Iwannacamp View Post
I donít own a MH


I did Google it and got tons of infoÖ. Assuming you may not have.
I searched 8.9 Cummins rear engine over heating.
I bet the answer is there
Yea I seen most of what comes up on that search. Best info is on having to manually downshift that Allison. I am sure there are users that have overcome this most of those posts are very old.

Thx Ted
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Old 07-14-2021, 08:31 PM   #8
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Originally Posted by Falconer View Post
Where are your Engine RPMs sitting? I don't know as much about the Cummins, but on my Duramax, I had similar issues until I started using manual mode and keeping the engine RPM above around 2300 going up hills. Went to manual mode on the trans, shifted down, kept RPM btw 2300 and 2800 and no more getting hot. That LBZ diesel would pull the grade just fine in high gear but it wouldn't shed the heat properly.
At first I have no clue as I was just driving. Having had a 330 Cat pulling the same jeep up the same grade, I figured this 425hp/1200 Tq could pull my 10000 K race trailer up the same grade??? Guess I though wrong.

To answer you question after the 1st shut down engine NOW warning, I paid more attention and tried to keep the RPM between 1500 and 1800. Later I started down shifting keeping the RPM higher this seemed to work better, but I had disconnected the Toad by then as I was close to home. All over heating came at 100* temps pulling at least a 5 to 5 % grade.

Thx Ted
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Old 07-15-2021, 12:28 PM   #9
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Temp readings?

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Originally Posted by Diego-Ted View Post
Got a new to me 41' pulling a Jeep Wrangler and the Coach gets hot looking at a hill. This happened coming to San Diego from Las Vegas pulling the 1st big hill. Chocked it up to Temp being 115*. Did it a second time pulling the the grade into Flagstaff from Phx at 97* temp? I am sure this should rig should be able to pull this with the small load we are pulling. Am I full of it? Any and all comment, Suggestions, I would be thankful for.

Ted
My 41 footer towing a Canyon pulling long hills heats up a fair bit even in much cooler weather. If the rig seems to struggle I manually drop a gear or two but typically its no big deal.
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Old 07-15-2021, 12:36 PM   #10
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Originally Posted by G Hollingsworth View Post
My 41 footer towing a Canyon pulling long hills heats up a fair bit even in much cooler weather. If the rig seems to struggle I manually drop a gear or two but typically its no big deal.
In hot weather 100* on a small grade pulling 65 mph I am in the 3/4 hot zone at the end of the cycle, then it will drop between 1/2 and 3/4 than creep up to 3/4 until the Thermostat opens. On a big climb the temp stays at 3/4 and flirts with the Stop Engine territory of the heat range. Once I disconnected the Jeep the Temps did drop maybe 20 percent and I was able to drive home with no over heat problems.

Another question, how fast are you climbing you major grades and In what gear. I had to go down to 3-4 to keep RPM above 2200 @ about 34-40 MPH and the temp stayed at 3/4.

thx Ted
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Old 07-15-2021, 01:52 PM   #11
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Originally Posted by Diego-Ted View Post
At first I have no clue as I was just driving. Having had a 330 Cat pulling the same jeep up the same grade, I figured this 425hp/1200 Tq could pull my 10000 K race trailer up the same grade??? Guess I though wrong.

To answer you question after the 1st shut down engine NOW warning, I paid more attention and tried to keep the RPM between 1500 and 1800. Later I started down shifting keeping the RPM higher this seemed to work better, but I had disconnected the Toad by then as I was close to home. All over heating came at 100* temps pulling at least a 5 to 5 % grade.

Thx Ted

There is a reason why you see all those 18 wheelers climbing the hills slowly. By keeping the RPMS up, as Falconer suggested you draw more air through the radiator resulting in cooler temps.


It will go up the hill fast, until it kills itself. Take your own observati9ons and go with them, Higher RPMS, slower speeds, cooler engine.
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Old 07-15-2021, 01:58 PM   #12
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At 115į you have to baby anything that is towing. That long climb from Phoenix to Flagstaff is a killer (even in the winter) and you definitely have to drive with engine temp in mind. After you learn your vehicle better and how to use shifting and rpms it should run cooler. The other option is to take it in to have radiator cleaned/flushed and thermostats/fan checked.
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Old 07-15-2021, 02:00 PM   #13
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Originally Posted by DouglasReid View Post
There is a reason why you see all those 18 wheelers climbing the hills slowly. By keeping the RPMS up, as Falconer suggested you draw more air through the radiator resulting in cooler temps.


It will go up the hill fast, until it kills itself. Take your own observati9ons and go with them, Higher RPMS, slower speeds, cooler engine.
Thank you, seems your advice is the prevailing school of wisdom; however, this coach is rated to pull 10K and my jeep weighs 2500? So if I was pulling my 10K race trailer I see where the advice is crucial, but with the jeep, I think it should not even be an issue?? Am I that far off from the real world?

thx Ted
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Old 07-15-2021, 02:41 PM   #14
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Well, you are in a motor home which is a load all by itself. Add 100 degree temps or extraordinay climbs like Phoenix to Flagstaff on I17, and you can overheat any motorhome if you drive it as you would on flat ground, towing or not. We have several friends with motorhomes and they have all learned how to make long, steep climbs with their individual rigs to keep engine temps lower.
My old lbz Duramax will climb anything while towing but will overheat if I don't adjust my driving. I lower the speed, lower the gear, raise rpms appropriately and the temp stays where it should.
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Old 07-15-2021, 03:43 PM   #15
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..................The other option is to take it in to have radiator cleaned/flushed and thermostats/fan checked.

VERY good idea for an engine that old. Have them look over the fan belt and hoses while they are in there., flush the coolant and refresh it (It DOES wear out as the additives are depleted)

NO sense letting a few dollars not spent on PM leave you steaming on the side of the road.

If I did that my right ear would be gone, chewed completely off by a VERY unhappy DW
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Old 07-15-2021, 06:03 PM   #16
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During a long up grade, Turn off your A/C. Turn on your heater full blast. (The small heater core in the heater will help cool things down.) Also, on a cold rear engine diesel, wash out/blow out accumilated dirt in the radiator from the engine side. In rare cases, (Heaven forbid.) check your engine's head gasket. Our 5.9 diesel started overheating at about 50,000 miles. After checking everything, Cummins found a head gasket seepage. It ran cool on mostly level roads but the coolant temp would slowly creep up on long upgrades. Also check the "sniffle tube" isn't spewing crankcase vapors on the radiator. I would always manually downshift the Allison trans to help keep the engine RPM/torque up. When I approach a grade, if I have room, I speed up a few MPH to assist the coach in climbing the grade. Safe & Happy travels
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Old 07-15-2021, 07:14 PM   #17
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Originally Posted by Diego-Ted View Post
Thank you, seems your advice is the prevailing school of wisdom; however, this coach is rated to pull 10K and my jeep weighs 2500? So if I was pulling my 10K race trailer I see where the advice is crucial, but with the jeep, I think it should not even be an issue?? Am I that far off from the real world?

thx Ted
While a vehicle can be rated to pull a specific load, that doesn't mean it will do it in high gear on a hot day up a long grade. Getting those RPMs up reduces engine temps in a hurry. Not only is more air coming through the radiator but the higher RPM, which gets you farther up the torque curve, reduces combustion chamber temps by hundreds of degrees in some cases. That in turn reduces the amount of heat that the cooling system needs to shed.
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Old 07-15-2021, 08:04 PM   #18
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Have your fan clutch checked for proper operation.
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Old 07-16-2021, 11:29 AM   #19
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VERY good idea for an engine that old. Have them look over the fan belt and hoses while they are in there., flush the coolant and refresh it (It DOES wear out as the additives are depleted)

NO sense letting a few dollars not spent on PM leave you steaming on the side of the road.

If I did that my right ear would be gone, chewed completely off by a VERY unhappy DW
Yep, all noted above, as well as sensors checked.

Diego
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Old 07-16-2021, 11:39 AM   #20
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Originally Posted by Falconer View Post
While a vehicle can be rated to pull a specific load, that doesn't mean it will do it in high gear on a hot day up a long grade. Getting those RPMs up reduces engine temps in a hurry. Not only is more air coming through the radiator but the higher RPM, which gets you farther up the torque curve, reduces combustion chamber temps by hundreds of degrees in some cases. That in turn reduces the amount of heat that the cooling system needs to shed.
I would hope to get more specifics to avoid as much trial and error as possible. Having to pull over on ZZXXXYYY grade coming South out of Vegas can be a Hazzard as there are places one cannot pull over to the side! SOS

I did not just mash the pedal, I did manage to keep the RPMS "1700" at what I thought was the recommended range to maximize engine torque? If everyone is saying around 2200 is better, than at what point at the begging of the pull all the way up. Sometimes due to traffic you are struck at the bottom of the grade pulling up without momentum?

Thx for all the help!
thx Ted.
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