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Old 06-20-2016, 01:57 PM   #1
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Overheating slight grade - ISB 6.7

New DP 2016 - Mileage ~3000

Last week on a trip from AZ to California on I10 I was on a stretch with a very slight climbing grade for several miles. I was in Economy mode and therefore it was staying in 6th gear, it was over 100 degrees outside and I was towing when engine overheated (check engine came on and temp gauge pegged). Pulled over and temp immediately came back down. Got back on the highway and back in same configuration it started to overheat again, so I took it out of Economy Mode which dropped it to 5th gear and it then started cooling back down.

When I returned to AZ I took it to Cummins, they did not find anything wrong.

On Friday I drove down to Tucson on hwy 79 southbound where there is a very slight grade for 30+ miles. In Economy Mode (6th gear), 100+ degrees, but not towing this time and engine temp starts to climb (past 3/4 on gauge but not quite in red). This time I take it out of Economy Mode immediately but no change in temp (it did stay in 6th), I then manually shifted to 5th, temp stopped climbing but did not come down, shifted to 4th (RPMís now around 2500+ I believe) and temp then slowly started coming down to normal (which seems to be at slightly below 1/2 on temp gauge).

Then I shifted back to 5th and eventually to 6th where it started the temp climbing process again. I then kept it out of Economy Mode and manually downshifted to 5th and 4th as needed until temp gauge seemed to fluctuate from 1/2 to slightly above 3/4 but did not go past that the rest of the trip.

On the return trip, which would be a slight grade downhill obviously, there was no temp issues. All remained normal in Economy mode the entire time.

So my question, is this considered normal on such a slight uphill grade?
And isn't that the purpose of economy mode, to stay in higher gear longer?

Is this simply a combination of the high outside temps and the slight grade? As I havenít had a chance to drive this coach yet in somewhat normal outside temp conditions.

Heading to NW next month where there will be a lot of climbing grades and donít want to overheat on a mountain pass! But I also shouldnít be in those extreme outside temps and I will be in lower gears which doesnít seem to be causing the issue.
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Old 06-20-2016, 02:14 PM   #2
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From what I read, the cooling system is not part of the engine. I know on a pickup with that engine the clutch fan controls cooling but when they put that engine in a mh, the cooling system is installed by the chassis mfg and is differernt than a truck. Maybe you need to go to who made the chassis. I don't think what you had happen is normal.
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Old 06-20-2016, 02:23 PM   #3
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Not unusual for temps going up when in 6th gear on an up hill grade. Automatic transmissions are good, but a driver that pays attention to temp gauge (and EGT if equipped) will know when the engine is at too low RPMs for the work it's doing. Manually shifting to a lower gear increases engine, water pump, and fan speeds, making for more heat removal.

If your fan is multi-speed, make sure it's kicking up to higher speed when engine starts to get hot. Also, when did you last clean off the radiator and cool pack? Rear radiators get dirty from road dirt and engine oil and can get quite inefficient when dirty.
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Old 06-20-2016, 02:32 PM   #4
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Quote:
Originally Posted by finnaz View Post
New DP 2016 - Mileage ~3000



Last week on a trip from AZ to California on I10 I was on a stretch with a very slight climbing grade for several miles. I was in Economy mode and therefore it was staying in 6th gear, it was over 100 degrees outside and I was towing when engine overheated (check engine came on and temp gauge pegged). Pulled over and temp immediately came back down. Got back on the highway and back in same configuration it started to overheat again, so I took it out of Economy Mode which dropped it to 5th gear and it then started cooling back down.



When I returned to AZ I took it to Cummins, they did not find anything wrong.



On Friday I drove down to Tucson on hwy 79 southbound where there is a very slight grade for 30+ miles. In Economy Mode (6th gear), 100+ degrees, but not towing this time and engine temp starts to climb (past 3/4 on gauge but not quite in red). This time I take it out of Economy Mode immediately but no change in temp (it did stay in 6th), I then manually shifted to 5th, temp stopped climbing but did not come down, shifted to 4th (RPMís now around 2500+ I believe) and temp then slowly started coming down to normal (which seems to be at slightly below 1/2 on temp gauge).



Then I shifted back to 5th and eventually to 6th where it started the temp climbing process again. I then kept it out of Economy Mode and manually downshifted to 5th and 4th as needed until temp gauge seemed to fluctuate from 1/2 to slightly above 3/4 but did not go past that the rest of the trip.



On the return trip, which would be a slight grade downhill obviously, there was no temp issues. All remained normal in Economy mode the entire time.



So my question, is this considered normal on such a slight uphill grade?

And isn't that the purpose of economy mode, to stay in higher gear longer?



Is this simply a combination of the high outside temps and the slight grade? As I havenít had a chance to drive this coach yet in somewhat normal outside temp conditions.



Heading to NW next month where there will be a lot of climbing grades and donít want to overheat on a mountain pass! But I also shouldnít be in those extreme outside temps and I will be in lower gears which doesnít seem to be causing the issue.

That is likely normal operation. Diesels produce lots of heat particularly when on a grade. To maximize cooling, the accepted technique for a long grade is to select a gear so that you will climb the grade at an RPM just below hp peak. I'm guessing your hp peak is around 2500. If you still find the Temp getting to high, down shift another gear and back out of the throttle slightly. If you can maintain 2400-2500 rpm without being at wide open throttle then that is the best situation from a cooling standpoint.

I think you have a rear radiator with an engine driven fan. The high rpm will maximize air flow through the radiator and maximize coolant flow inside the cooling system.
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Old 06-20-2016, 02:36 PM   #5
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Recommend on any grade greater than about 4%, or when your temp starts to climb on a grade, that you disengage the economy mode and let the ECM find a better gear for climbing. You did it right by manually selecting a lower gear, reducing some speed, and letting the RPM come up to ~ 2000. Its more important to keep your RPM up than your speed - and you'll find the right balance as you get more familiar with your coach's abilities.

Better yet - on any grade you encounter on your next few drives - disengage the economy mode and start at the bottom of the grade with this process - and see what happens to your temps.

On the flip side of the hill - remember you will probably need to manually select a lower gear to keep your speed down. It's often said that you should start by selecting the same gear that you climbed the hill in - and then adjust from there.

Safe travels ... let us know what you experience ... we all learn ...
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Old 06-20-2016, 05:28 PM   #6
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Quote:
Originally Posted by BFlinn181 View Post
Not unusual for temps going up when in 6th gear on an up hill grade. Automatic transmissions are good, but a driver that pays attention to temp gauge (and EGT if equipped) will know when the engine is at too low RPMs for the work it's doing. Manually shifting to a lower gear increases engine, water pump, and fan speeds, making for more heat removal.

If your fan is multi-speed, make sure it's kicking up to higher speed when engine starts to get hot. Also, when did you last clean off the radiator and cool pack? Rear radiators get dirty from road dirt and engine oil and can get quite inefficient when dirty.
I seriously doubt that a new coach with 3000 miles is going to have radiator blockage. Unless things have really changed I don't think an engine should have more than about 10 degrees rise over normal operating temp. I pulled my trailer up a 15% grade and it only went up to about 210 degrees. Ask at a shop if that's normal but I don't believe it is.
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Old 06-20-2016, 05:38 PM   #7
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I seriously doubt that a new coach with 3000 miles is going to have radiator blockage. Unless things have really changed I don't think an engine should have more than about 10 degrees rise over normal operating temp. I pulled my trailer up a 15% grade and it only went up to about 210 degrees. Ask at a shop if that's normal but I don't believe it is.
I was just covering all possibilities. A plastic bag sucked up into the radiator can happen in the first mile. On a diesel engine in a large RV temperature rise is very normal. The engine is working hard and is going to create heat. Downshifting is a way to increase RPMs and shed heat faster.
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Old 06-20-2016, 06:07 PM   #8
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This was just odd for me because both times it was a very slight grade. The type of grade that you don't know you are even climbing other than transmission may downshift and you wonder why is it doing that
In this case it caught me off guard because of that. I expect temps to go up on a good climb, but wasn't expecting it in this scenario. I haven't yet had a chance to get it out on a 4-6%+ grade to really test it out. Soon though.

Previous coach was a front engine diesel and engine temps wasn't much of an issue.

Hopefully this is just a learning curve. I need to take it to Freightliner for some other non-related issues so I will ask them about it as well.

For additional notes, it is an XCS Series chassis with '1335 cubic-in rear-mounted radiator remote-mounted water to oil belt-driven with viscous fan clutch.'
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Old 06-20-2016, 09:10 PM   #9
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I'm pretty sure that is not normal. I do know that when you lug the engine the egt will go up fast but by what you said water temps shouldn't rise like that. I read a thread recently where freightliner had an issue with several people having problems heating up just like you say. I would definitely have them check it out before you really run it too hot and cause more problems.

Just a thought. Are you sure the gauge is correct? Do you have a scangaugeD or the like to know exactly what temp the engine is operating it?

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Old 06-20-2016, 10:25 PM   #10
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I'm pretty sure that is not normal. I do know that when you lug the engine the egt will go up fast but by what you said water temps shouldn't rise like that. I read a thread recently where freightliner had an issue with several people having problems heating up just like you say. I would definitely have them check it out before you really run it too hot and cause more problems.

Just a thought. Are you sure the gauge is correct? Do you have a scangaugeD or the like to know exactly what temp the engine is operating it?

Chad
Unfortunately I sold my scanguage with the previous coach as I didn't think I would need it with the new FL message center on this coach. When Cummins checked it, they did see two engine overheat codes captured. Not sure if that is tied to the analog gauge or the digital readout in the message center? I did not have the engine temp configured in the message center at the time only the transmission temp which has always stayed normal between 195 and about 202.
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Old 06-20-2016, 10:49 PM   #11
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Could be any number of things including fan not engaging correctly, sticky themostat, something sucked into fan shroud. Engine lugging up hill will definetly cause heating issues too. If you notice it getting hot manually downshift and keep the rpm's up over 2000. The faster you turn the motor the faster the water pump turns and the faster the fan spins. Unfortunately the engine/transmission system isn't smart enough to shift itself due to temperature issues. Something could be wrong even with a brand new coach unfortunately.
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Old 06-20-2016, 11:27 PM   #12
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What you are seeing is perfectly normal operation. You cannot lug the engine at full power and low RPM and expect it to stay at normal temp. You also cannot just put these vehicles in D and drive. These coaches are not cars.

It is SOP to get the engine up to max HP RPM to climb a grade. That does two things:
1) Makes sure the engine is turning over at an RPM where max HP is available to climb the grade
2) Spins the engine fast enough to circulate the water faster and run the fan faster to keep the temp down.

I will say it again...you CANNOT just put the tranny in D and drive and expect to get the best performance out of your coach. You have to make decisions about how to drive the coach depending on where you are and what you're doing. And that means manually shifting down on long, steep grades.
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Old 06-21-2016, 12:41 AM   #13
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You have a similar length and weight coach as I do, along with the same engine. I do not experience the same conditions which you have. I would strongly suggest you get the fan clutch checked out. You don't mention if you can hear it come on-line when the temp starts to climb. I can certainly hear mine. There have been issues as stated on several postings regarding the fan equipment. I can agree with others above that you need to respond to conditions while driving up and down grades, but the grades you describe should not affect your temp to the degree you describe. I do find it best to shut off the dash, engine powered air conditioning while climbing higher grades. That's not what your DW wants to hear but it does help the temp issue.
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Old 06-21-2016, 10:43 PM   #14
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You basically figured it out on your own. Take it out of economy mode and keep the RPMs up above 2,000 and it will keep the temperatures in normal range. I have tried economy mode some, but from what I understand it only works well in flat terrain.
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