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Old 06-14-2011, 01:04 PM   #1
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Hills, Texas heat and engine temps??

All:

Just came back from two days of driving in the NE. Texas in the hills. It was 97 degrees, slight head wind, and on one long hill the engine temp warning light came on. I crested the hill and slowed my speed from 65 to 55 and the temp went right back to normal. Over the next two hours I kept the tranny in a lower gear and the rpms up around 2000 on all other hills and the gauge never passed midway.

Upon arriving home and a cool engine I inspected the coolant level and it looked fine. Is this heat rise typicall? I have no leaks and have not had any problems in the past. This is my first MH and I have only been driving this one since October. I went back through the manual, and it seems that I should have been in the lower gear higher RPM to begin with. I guess this is why they install gauges and maybe I need to learn to pay closer attention!

Thanks in advance for your comments and advise.

Dave
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Old 06-14-2011, 01:09 PM   #2
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Not to seem like I'm being funny but maybe slow it down a little, that's a lot of frontal area to be pushing up hill at 65MPH, I know a lot of you others can do it with no problem .
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Old 06-14-2011, 01:50 PM   #3
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I don't disagree at all! I am trying to learn the MH and on lower hills found that it preferred 65 in 6th gear. The manual says to find the right spot that it climbs without shifting that the cummins likes that and does not need to be reved up. However, the manual also says to shift down and rev up the rpms on hot or hilly days...I think you are correct and that is why I am looking for answers from more experienced drivers.

Thanks,

Dave
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Old 06-14-2011, 02:04 PM   #4
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Hi,

I don't own a diesel pusher but have a 8.1 l gas engine and when approaching a hil I first get out of overdrive and then as speed decreases I downshift to the next gear which usually takes me over the top and I use the same car going down the hill for braking.

WE are in agrweement with the former post and that is to slow down. Usually rvers are not in a hurry and like to take time to smell the roses. So even though you have quite a bit of torgue on that DP slow down and enjoy the view, life is good!
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Old 06-14-2011, 02:40 PM   #5
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I found if I keep my RPM's around 2000-2100 on long climbs, the temp never goes any higher than normal. Basically, don't let the engine lug and the temp seems to be just fine. For me, it's generally dropping down to 5th and probably 4th if it's a relatively long climb.
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Old 06-14-2011, 03:15 PM   #6
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Hi Dave,
At one time there was a link to a Cummins website where you could plug in you engine size, type of driving and speed and it would give an RPM range where you should keep the engine for the optimum performance. For my ISL driving between 60 and 65 MPH my “sweet spot” was between 1350 and 1900 RPM. When I dive the hills/mountains I put the transmission in whatever gear that keeps the RPM in the sweet spot, regardless of my speed. What I discovered was whatever gear the engine was in going up the hill/mountain it was perfect going down the other side coupled with the use of the exhaust brake.


I wish I could find the Cummins link, but I did find this older thread about the same problem you have described.
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Old 06-14-2011, 04:00 PM   #7
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Dave1956,

I was in Texas just last week. OAT between Wichita Falls and Dallas was 103 to 105. Those temps combined with a little headwind cause my temp to rise from about 1/3 scale to a little over 1/2. 1700 rpm is just not enough to cool it under those conditions and slowing down doesn't seem to matter. What does matter is getting the fan speed up around 2000.
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Old 06-14-2011, 04:10 PM   #8
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Quote:
Originally Posted by Dave1956 View Post
All:

Just came back from two days of driving in the NE. Texas in the hills. It was 97 degrees, slight head wind, and on one long hill the engine temp warning light came on. I crested the hill and slowed my speed from 65 to 55 and the temp went right back to normal. Over the next two hours I kept the tranny in a lower gear and the rpms up around 2000 on all other hills and the gauge never passed midway.

Dave
The Cummins ISL has a very high torque rating for an engine in its displacement category. While the ECM can deliver the fuel to climb hills in higher gears, you have found that you pay for that torque rise ability in other ways. When the engine lugs to lower RPM and the torque output climbs as you approach peak torque RPM, the result is the fuel delivery is increased such that more power is produced at a time when fan speed is less than optimum and water pump RPM is reduced. The net result is the engine is producing heat faster than the radiator can remove it.

By shifting down as others have well stated, you increase fan speed, water pump RPM and reduce the fuel delivery rate such that the heat rejection from the engine into the coolant is matched by the radiator' rate of heat removal......the engine remains in a cooler mode as witnessed by the lower temp gauge reading.

That is a "drawback" tp tjhe ISL...it has plenty of guts, too much in some cases.

When you exceed 55 MPH, the air drag horsepower requirement increases exponentially, not linearly. Meaning the HP requirement to maintain 65 against a headwind requires LOTS more fuel delivery to keep the torque output up.

You were right to shift down and save the engine as well as the transmission. Keep in mind that the transmission oil cooler suffers those low RPM, high load issues from reduced fan speed and air flow and coolant flow if it is cooled by engine jacket water.
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Old 06-14-2011, 07:18 PM   #9
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Thanks you guys are a great source in information and this helps me to learn the proper use of my coach!
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Old 06-17-2011, 11:26 AM   #10
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Hi, F/L web site says that Cummins recomends cleaning the rad and intercooler every 7500miles, more often in dusty conditions. You've made no mention of doing this so I thought I'd throw it in.
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Old 06-17-2011, 12:25 PM   #11
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Follow up

Got the part about climbing hills during hot weather and what to do about it. How about when you're stuck crawling in Chicago traffic, say around 3:00PM on a Friday, it's 100F, and you've been doing that for 1-1/2 hours? Been there, done that, and won't do it again.
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