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Old 06-12-2013, 12:50 PM   #1
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Hill climbing procedures

Just climbed the grade northbound I75 just south of Kentucky border. This was my first steep grade (not counting Florida hills.

I had the engine at 100% load going about 48 MPH with the transmission in auto (letting it select the gear).
Water temp got to 205F.
Should I have selected a lower gear manually and maybe not run at 100% load?
If it does get too hot I figure you pull over and let it cool.

I do use the selector for down grade and it works well keeping speeds and temperatures within range.

Thanks
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Old 06-12-2013, 12:54 PM   #2
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Hill climbing

I definitely suggest taking it off cruise control and manually slecting RPMs and gears for hill climbing. It is not necessary to go fast over the hills. Stay in the right lane and use as low an RPM as possible to climb. 40 MPH to 45 MPH may be the fastest, but that is okay. Running the engine until it overheats, then pulling over to cool down is not good. Steady, even speed is better.

Happy Trails!

Darryl
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Old 06-12-2013, 01:03 PM   #3
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I downshift when the temperature rises more than I am happy with. On a big climb on a hot day I just keep the revs between 1800-2100 and the engine seems happy. Most of the time I can just let the cruise control and the Allison sort things out.
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Old 06-12-2013, 01:33 PM   #4
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Quote:
Originally Posted by desobelman View Post
I definitely suggest taking it off cruise control and manually slecting RPMs and gears for hill climbing. It is not necessary to go fast over the hills. Stay in the right lane and use as low an RPM as possible to climb. 40 MPH to 45 MPH may be the fastest, but that is okay. Running the engine until it overheats, then pulling over to cool down is not good. Steady, even speed is better.

Happy Trails!

Darryl
I agree with 90% of what you said but I am going to disagree a bit about the RPM thing. At the Spartan factory owners training course they said the opposite about RPM. What we learned was that the fan speed was affected by the engine RPM and that low RPM reduced cooling. In the case of a hydraulic controlled ISL the maximum fan speed was based on the engine RPM since that also drives the pump. In the case of the ISX there is a belt that drives the fan speed. I can't speak for CAT and other chassis manufacturers so I leave that to others to comment on.

So...when I cruise the flat lands at about 62 MPH, if I remember correctly my RPM is about 1750. Approaching a big climb I would attack it by manually selecting a gear to put me at about 1900 RPM before I started to feel it and if needed select an even lower gear as the climb continued to keep me close to 1900 RPM. If I was able to maintain the safe speed for that climb at 1900 RPM I would be satisfied and not be too tempted to shift up for lower RPMs. If I couldn't hold 1900 RPM I would then shift to a lower gear to get back there.

As a bicyclist I have had to learn how to read the terrain and select a proper gear and cadence going into the climb before my legs blow up. As an example, if it is a long, steep climb, I have to gear down, increase my peddle rate and grind it out at any speed it allows without making my legs suffer. If I use to high of a gear my legs will glow up, I will over heat and I am going to have to walk it up to the top. The same principle applies to the MH. You need to be ahead of the power curve and anticipate the proper gear selection. If you get behind power curve, it is very tough to catch up and get back into a nice groove if you let the RPM get too low and the engine temps too high. Plan ahead and be prepared before you hit the climb. It is easier to upshift to a taller gear if you over estimate a climb than it is to down shift and regain momentum if you underestimate it.

All is written with the implied caveat of...IMHO
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Old 06-12-2013, 02:40 PM   #5
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Jeff753, that is a tricky climb, as you noticed there are two places that that you feel you could upshift if you where in fact operqting your coach. Not being critical but, you weren't operating it you were just steering. Allowing the cc to make operation decisions while pulling a grade is bad business. Here is what happened: When you exitied the tunnel with the cruise on you most likely running at about 50, the road flattens out enough for the trans to make one upsift putting in direct or 5th gear. Then the pull begins, being in fifth the rpms were about 2000 and you began to pull the hill, the CC tells tells the motor you want to go 62, the computer makes some calculations and decides that since the motor is with the operationl perameters (rpm range) it will not tell the trans to downshift. The rpm is too low to be efficient but still high enough to satisfy the computer. Meanwhile, the fan and water pump are not spinning fast enough to properly cool the motor but the motor continues to try to meet the demands of the computer because of the CC. By now you have reached one of those points on the hill that you actually pick up a little speed but the increased rpms are short lived because you've reach another point where the motor has to start working hard again. Given the short period when the higher rpms produced more cooling effort the motor never really got a chance to relax. Depending on the time of day you were pulling your most likely on the number two lane keeping an eye on traffic as it gets pretty crazy at certain times with folks shooting for the several exits along the way.

Without repeating the whole process, it continues as you reach the top. You finally get the chance to take a breath and look around when you notice the temp guage at 205. Nothing to worry really but your probably a bit alarmed. Should this happen again, the worst thing you can do is pull over and let the motor idle. Remember, higher RPMs equate to better cooling and at this point that is what your motor needed. By the time you passed Kings Island things should have been back to normal and smooth sailing from then on.

I certainly did not want to bore you with this or sound preachy but, don't be afraid to shift the trans yourself, there are built in safeguards that will prevent the engine from over speeding if you attempt to shift into too low a gear. Because you can't really hear the engine its important to keep and eye on the tachometer and temp guage. When pulling, keep the engine at the higher end of its operating range and you'll be alright. Regards.
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Old 06-12-2013, 02:48 PM   #6
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great reply Coaster, thank you
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Old 06-12-2013, 02:50 PM   #7
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I'm not sure what road you're talking about, but there's no tunnel on I-75 in Kentucky or Tennessee that I'm aware of. I think the OP was talking about Jellico.

Quote:
Originally Posted by Coaster1 View Post
Jeff753, that is a tricky climb, as you noticed there are two places that that you feel you could upshift if you where in fact operqting your coach. Not being critical but, you weren't operating it you were just steering. Allowing the cc to make operation decisions while pulling a grade is bad business. Here is what happened: When you exitied the tunnel with the cruise on you most likely running at about 50, the road flattens out enough for the trans to make one upsift putting in direct or 5th gear. Then the pull begins, being in fifth the rpms were about 2000 and you began to pull the hill, the CC tells tells the motor you want to go 62, the computer makes some calculations and decides that since the motor is with the operationl perameters (rpm range) it will not tell the trans to downshift. The rpm is too low to be efficient but still high enough to satisfy the computer. Meanwhile, the fan and water pump are not spinning fast enough to properly cool the motor but the motor continues to try to meet the demands of the computer because of the CC. By now you have reached one of those points on the hill that you actually pick up a little speed but the increased rpms are short lived because you've reach another point where the motor has to start working hard again. Given the short period when the higher rpms produced more cooling effort the motor never really got a chance to relax. Depending on the time of day you were pulling your most likely on the number two lane keeping an eye on traffic as it gets pretty crazy at certain times with folks shooting for the several exits along the way. at the higher end of its operating range and you'll be alright. Regards.
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Old 06-12-2013, 02:56 PM   #8
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You may be right!. When i first red the post I got my directions backwards and thought he was heading north out of Cincinnati, OHio.
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Old 06-12-2013, 03:00 PM   #9
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Quote:
Originally Posted by Jeff753 View Post
Just climbed the grade northbound I75 just south of Kentucky border. This was my first steep grade (not counting Florida hills....
Was that just south of the TN-KY border north of Knoxville near Jelico?
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Old 06-12-2013, 03:03 PM   #10
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If you're on northbound I-75 just south of the Kentucky border, you're in Tennessee, not Ohio. There's still no tunnel on I-75 anywhere in Kentucky.
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Old 06-12-2013, 03:13 PM   #11
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I'm not here to argue geography. I admitted my error, and I never said there was a tunnel in Kentucky.
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Old 06-12-2013, 03:17 PM   #12
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I tackle hills just as Sky-Boss does, downshifting as needed to keep my RPM's at 2000, and have never had a problem with my ISL/side radiator.
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Old 06-12-2013, 03:21 PM   #13
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Jeff wait until you get out west. Use lower gears, keep rpms up, and minimize upshifting when you know that you are about to descend/ascend shortly. Your engine and transmission will run cooler. This will increase the quality of your ride due to undue shifting under load and abrupt downshifts, along with the anxiety of temps climbing.

I limit my Allison to 4th on the state highways that are up and down and twisty. The kind they have in Arizona, Utah, and CO. I typically drive those sections 40-55 mph and have no issues with climbs or descents. Occasionally, I hold up a little traffic, typically I end up being held up due to tractor trailers on these roads.

The interstates typically are limited to the curve radius and grade, so I mostly will run those with CC on in 6th gear.
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Old 06-12-2013, 03:50 PM   #14
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The "right" RPMs depends on what engine he has, so any numbers shown above may well be improper ones. In general, higher RPMs means more cooling, but when climbing a grade(i.e. heavy load) it also means higher engine temperatures. Moderation is the key, keeping engine rpms up but not overtaxing the cooling system. For best performance and cooling, keep the engine between the peak torque RPM and the peak horsepower rpm for your engine. Your Allison will do that for you in 99+% of the cases, so not much need to second guess it. Most Allisons are programmed to stay at the max horsepower rpm when under load.

You do, however, need to control the speed (which is why Cruise is not a great idea for any terrain with lots of grades to climb or descend). Run at a speed that lets the engine perform in its prime rpm range while minimizing the impact on heating. 205 is nowhere near dangerous to your engine, but it's a warning that it is working hard. Slow down and give it a rest.

If the engine continues to heat up, pull over as soon as you can, put the tranny in neutral, and then increase engine RPMs to maximize cooling. More RPMs with no engine load improves both coolant circulation and air flow through the radiator. With no load (tranny in neutral), the increased rpms generates very little extra heat.
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