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Old 06-21-2021, 08:51 AM   #1
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Question High Engine Temp on steep grade

Over the past month we have been traveling across the Southwest through Texas, New Mexico, and Arizona. With desert high temperatures and flat roads I've never seen the engine temp above 200. However, last week that changed. While going up a long 6 degree grade on I-17 between Phoenix and Flagstaff the engine temp reached 221 and threw a "Engine Temp Threshold" warning. The outside temperature that day was 110+ degrees.

My rig has an Cummins 8.9 liter Turbo 400 ISL and Allison 3000 tranny. They were serviced by Freightliner Gaffney, SC. December 2020.

My driving experience is limited to the Southeast, so I've never had to negotiate a steep grade like that and I've never seen the engine temp above 200.

Could the high temp warning have been caused by my driving style and something I did? You see, While going up the grade I got stuck behind an 18 wheeler doing 25mph so when I had a chance, I floored it and passed the 18 wheeler. I kept the throttle on the floor until I noticed the temp warning. I backed off the throttle and the temp stabilized at 119 but still above the temp threshold and throwing the warning. At the top of the grade I pulled to the shoulder and the temp return to 197.

Does going up a steep grade require any special driving technique to maintain a safe engine temp or did I do something wrong?
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Old 06-21-2021, 09:43 AM   #2
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Noticing that your rig is a 2006 I would suspect that it is time to clean the radiator and Charge air cooler. The best would be to have them steam cleaned but in a pinch you can buy pressurized cans of de greaser and spray them let it set for a bit then spray them off with a hose. Secondly when climbing a long hill if you see the temp climbing manually drop it down a gear to increase the speed of the fan. Of course this only works if you don't have an electric fan.
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Old 06-21-2021, 09:50 AM   #3
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Agree on cleaning the CAC and radiator.


And, yes, there is a "driving style" that minimizes overheating.


Use the Allison down arrow to select a gear where engine RPM is around 2000 and where you are just short of WOT. Said another way, if you floor it you will still accelerate a little.


If overheating and you can pullover, do. Hold engine RPM 1200-1500 in neutral. Unless you have overheating due to coolant loss, temperature will quickly come down.


If you can't pull over, put the dash heater to full hot and fan speed to high-- think of it as a "spare radiator". Better to be hot for a few minutes than significantly lighten your wallet.
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Old 06-21-2021, 03:53 PM   #4
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Agree to keeping the RPMs at 2000. Also there was a changeover to 15W40 oil for the powersteering/cooling fluid and a new cooler. The Original dexron III fluid in there cavitated and increased the likely hood of overheating.

Check with Freightliner. I had a 2005 40KD Horizon and had that change performed. Never saw overheating again after that.
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Old 06-22-2021, 08:54 PM   #5
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If you made that drive in 110 degree heat you did great. I would never try that in my dynasty. I wait until midnight when the temps drop to 90 in the desert.
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Old 06-22-2021, 10:07 PM   #6
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hey so I saw where you mentioned the use of engine oil in the power steering, was that for all vehicles or specific ones. I had just changed my filter in the ps and the color was that of oil rather than Dextron. Was that some kind of tech bulletin or ???
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Old 06-22-2021, 10:14 PM   #7
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Quote:
Originally Posted by KD4XR View Post
Over the past month we have been traveling across the Southwest through Texas, New Mexico, and Arizona. With desert high temperatures and flat roads I've never seen the engine temp above 200. However, last week that changed. While going up a long 6 degree grade on I-17 between Phoenix and Flagstaff the engine temp reached 221 and threw a "Engine Temp Threshold" warning. The outside temperature that day was 110+ degrees.

My rig has an Cummins 8.9 liter Turbo 400 ISL and Allison 3000 tranny. They were serviced by Freightliner Gaffney, SC. December 2020.

My driving experience is limited to the Southeast, so I've never had to negotiate a steep grade like that and I've never seen the engine temp above 200.

Could the high temp warning have been caused by my driving style and something I did? You see, While going up the grade I got stuck behind an 18 wheeler doing 25mph so when I had a chance, I floored it and passed the 18 wheeler. I kept the throttle on the floor until I noticed the temp warning. I backed off the throttle and the temp stabilized at 119 but still above the temp threshold and throwing the warning. At the top of the grade I pulled to the shoulder and the temp return to 197.

Does going up a steep grade require any special driving technique to maintain a safe engine temp or did I do something wrong?

Slow down, do as the truckers do. I too have the same engine as you. In the heat of summer in AZ I often disconnect the toad and have my wife drive it.
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Old 06-22-2021, 10:46 PM   #8
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As others have mentioned, drop down a gar and keep it about 2,000 RPM. You need to keep the engine at high RPM to keep the fluid circulating faster. I have had to drop 2 gears at times to keep my engine temps down.
This also applied when I was driving an 18 wheeler.
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Old 06-29-2021, 08:13 AM   #9
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Thanks for all your comments and suggestions. Tomorrow, we are headed to our next destination and up another steep incline. I'll give these suggestions a try and let y'all know how it goes..
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Old 06-29-2021, 05:03 PM   #10
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hey so I saw where you mentioned the use of engine oil in the power steering, was that for all vehicles or specific ones. I had just changed my filter in the ps and the color was that of oil rather than Dextron. Was that some kind of tech bulletin or ???
Do not use motor oil in the hydraulic system! Use what the mfgr specified on the label on the reservoir, most use an AW type oil of differing grades, the lower the number the lower the viscosity.
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Old 07-01-2021, 09:37 AM   #11
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Yesterday we left Camp Verde, AZ and headed south on Interstate 17 toward Phoenix. As soon as we jumped on the Interstate we were faced with a 5 mile 6% grade. So, remembering your advice, I slowed to 55mph and dropped the tranny back to 4th gear. The engine rpm was about 2200, engine temp topped out at 204, and outside air temp was 100 degrees. I am pleased with that result. Thanks for the advice.
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Old 07-01-2021, 09:45 AM   #12
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Yesterday we left Camp Verde, AZ and headed south on Interstate 17 toward Phoenix. As soon as we jumped on the Interstate we were faced with a 5 mile 6% grade. So, remembering your advice, I slowed to 55mph and dropped the tranny back to 4th gear. The engine rpm was about 2200, engine temp topped out at 204, and outside air temp was 100 degrees. I am pleased with that result. Thanks for the advice.
For cheap insurance plus you may not know if it has ever been replaced, I would replace your engine thermostat with a original Cummins 180* one. 10 minute job and about a $20 replacement. It was a 10 minute job on my coach. Prolly the same on a 400.
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Old 07-01-2021, 07:58 PM   #13
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You drove an older rig uphill, I-17, 110F, floored? What did you expect?
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Old 07-02-2021, 10:14 AM   #14
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Originally Posted by KD4XR View Post
Yesterday we left Camp Verde, AZ and headed south on Interstate 17 toward Phoenix. As soon as we jumped on the Interstate we were faced with a 5 mile 6% grade. So, remembering your advice, I slowed to 55mph and dropped the tranny back to 4th gear. The engine rpm was about 2200, engine temp topped out at 204, and outside air temp was 100 degrees. I am pleased with that result. Thanks for the advice.
No that grade well! From basically 5-10MPH On Ramp turn, to Pedal to the Metal hill climb!

If you have not done it yet, suggest you get your specific engine serial number and call Cummins Tech Support. Ask them if they can send you, or point you at, a HP/Torque to RPM Curve Chart. (ISL's were built over many years, and different version's of the ISL have different HP/Torque Curves. Also ask them for Max RPM while under power, and Max RPM when using either Jake Compression, and or Exhaust Brake, assist whichever is appropriate for your engine. (CAPS ERA ISL (From memory.) had 2350 Max RPM (I kept her between 2000-2200, preferred 2050-2150 for serious hill climbing. And found when getting a running start, and down shifting at about the 1650-1750 range, she'd usually pull most grades well in the 1750-2050 range. On SERIOUS LONG HILL CLIMBS, 2050-2150 earlier then later, is what I'd do.) Jake Compression Max RPM was 2600, and I'd usually Stab The Brakes and slow down, when it got to 2500 or so RPM.) Again, 2003 CAPS era ISL. For sure, Variable Geometry Turbo ISL's would be different!

Enjoy your coach, and have some fun,
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