Mountain passes

[bwalz]

I'm sure this has been asked before but here we go again! We have a Series 60 and are about to embark "over the hump." Previously in a 40' Prevost I overheated and was told at the time my RPM's were too low.
When consulting a friend wih a 45' Series 60 he suggested gearing to run at 2000 RPM's to avoid problems.
Any experienced high altitude guru's out there??

[MangoMike]

I'll be interested to see what the pros post. But my last trip out west I kept it at 15-1600 and watched the temps w/ no problem. 2000 seems high to me.

I was more worried about the down side.

Mike

[bwalz]

2000 seemed high to me also. I've always thought 1800 to be the top side of safe.

[Petervs]

Well, I do not know if I am a pro or not, but I have 50,000 miles on my series 60 driving all over. We live in the west, and most trips involve going over a pass here or there.

Many interstate passes are 6% grades and some climb to 6000 feet or more. We have been to 10,000 feet. Many of the smaller highways also have good climbs, usually with more twisty parts and not so much a steady long even pull.

In any case, I drive up the hills with the transmission in Drive and the pedal to the metal. The two speed fan keeps the coolant temp in line without any problem, even on hot days. The DDEC keeps anything harmful from happening. The RPM falls where it will. Peak torque is around 1500 rpm, so that is the most powerful way to climb the hill.

Going down, I choose the gear that when the Jake Brake is on keeps the speed around 55 or so.

My technique would be different if I had an 8V92.

Basicall with the Series 60, "Don't worry, be happy!"

[garyde]

I either chang to 'economy mode' on the transmission or shift down a gear when my speed drops below 50. The RPM's go up at that point and max's out at about 2000. I have not had any major temp. rise in either case.

[Jon Wehrenberg]

We have a 6% grade that extends for miles that we climb and descend about 3 or four times a year. When we lived in our previous home we took a route that covered another 6% grade also extending for quite a while. That hill we often climbed with our 8V92. The altitudes were fairly low however so that affects cooling capability beneficially.

In both our 8V92 and the Series 60 I select the gear that will allow me to go up the hill as fast as I can. In both coaches I hit the bottom of the hill higher than normal speed in the gear that I knew would hold the best speed to the top. In the 8V92 I had the 5 speed Allison and if I could keep the revs to 1800 or above in fifth I could hold the speed all the way. My temps would hit 195 to 205 or thereabouts and stabilize. My foot was on the floor all the way.

The Series 60 with the six speed is no different. I generally drop a gear to fifth, put it in performance mode, start accelerating before I get to the upgrade, and it will drop back to a stabilized speed of between 55 to 60. The temps stay right around 205 or 210 and are stabilized. My foot is on the floor from the bottom to the top.

I have run these grades in cold temperatures and hot. In colder temperatures the engine stays slightly cooler, but in 95 degree temps the engine temps are what I described.

If you have to screw around with RPMs, gears, different speeds, etc. to hold the temps at a stabilized point within an acceptable range you do not need to learn hill climbing techniques, you need to service your cooling system and possibly recore the radiator. If you think I am blowing smoke, I run these hills in the heat of summer with the OTR keeping us cool dragging a H2 Hummer.

[0533]

We have a 6% grade that extends for miles that we climb and descend about 3 or four times a year. When we lived in our previous home we took a route that covered another 6% grade also extending for quite a while. That hill we often climbed with our 8V92. The altitudes were fairly low however so that affects cooling capability beneficially.

In both our 8V92 and the Series 60 I select the gear that will allow me to go up the hill as fast as I can. In both coaches I hit the bottom of the hill higher than normal speed in the gear that I knew would hold the best speed to the top. In the 8V92 I had the 5 speed Allison and if I could keep the revs to 1800 or above in fifth I could hold the speed all the way. My temps would hit 195 to 205 or thereabouts and stabilize. My foot was on the floor all the way.

The Series 60 with the six speed is no different. I generally drop a gear to fifth, put it in performance mode, start accelerating before I get to the upgrade, and it will drop back to a stabilized speed of between 55 to 60. The temps stay right around 205 or 210 and are stabilized. My foot is on the floor from the bottom to the top.

I have run these grades in cold temperatures and hot. In colder temperatures the engine stays slightly cooler, but in 95 degree temps the engine temps are what I described.

If you have to screw around with RPMs, gears, different speeds, etc. to hold the temps at a stabilized point within an acceptable range you do not need to learn hill climbing techniques, you need to service your cooling system and possibly recore the radiator. If you think I am blowing smoke, I run these hills in the heat of summer with the OTR keeping us cool dragging a H2 Hummer.
One Question Jon. You said that you switch from Economy mode to performance mode as you are preparing to climb the hill? If so then its ok to make these changes to the mode setting on the fly in either direction? I really need to read the Prevost manual.

I have never used anything but economy mode in an effort to save some fuel, but am now thinking that its a mistake when climbing and even descending large grades. I noticed on my trip across from Coburg that I had many occasions where the extra torque would have been helpful, and if applied might have keep the temps in check better.

[Jon Wehrenberg]

You can switch transmission modes at any time.

All that is happening when you go from one mode to another is changing the shifting parameters. In economy mode the transmission will upshift sooner, downshift later, and tend to have softer shifts. It is keeping the engine in a lower RPM range where torque is high, and HP is low for the best fuel efficiency.

In performance mode the shifts will occur at higher RPM, downshifts will occur much sooner, especially if the transmission senses a load such as a hill, and the shifts will tend to be more abrupt or agressive. By using this mode at the base of a hill I can hold the coach in a lower gear longer. This will prevent an upshift to a gear that cannot maintain the desired speed and the constant "hunting" of the transmission as it shifts up and down.

The only thing happening when you shift from mode to mode is a change in the shifting program. There is no internal shifting of gears such as going from low range to high range in a transfer case on a 4WD vehicle.

[MangoMike]

As I recall at POG 4, Bill Jenson from Prevost said that performance mode added 200 rpm to the shift cycle.

[0533]

You can switch transmission modes at any time.

All that is happening when you go from one mode to another is changing the shifting parameters. In economy mode the transmission will upshift sooner, downshift later, and tend to have softer shifts. It is keeping the engine in a lower RPM range where torque is high, and HP is low for the best fuel efficiency.

In performance mode the shifts will occur at higher RPM, downshifts will occur much sooner, especially if the transmission senses a load such as a hill, and the shifts will tend to be more abrupt or agressive. By using this mode at the base of a hill I can hold the coach in a lower gear longer. This will prevent an upshift to a gear that cannot maintain the desired speed and the constant "hunting" of the transmission as it shifts up and down.

The only thing happening when you shift from mode to mode is a change in the shifting program. There is no internal shifting of gears such as going from low range to high range in a transfer case on a 4WD vehicle.
So then I would simply press the mode button one time in each direction???? to change back and forth between modes??? Nothing comes up in the window that says Economy/Performance??? I just will notice the difference when the auto shift kicks in, RPM's etc?

[0533]

As I recall at POG 4, Bill Jenson from Prevost said that performance mode added 200 rpm to the shift cycle.
200 RPM will make a substantial difference in the power, as I am often too late on the hill climb waiting for the economy mode to sense the hill and make the shift.

Mango, you should replace your Avatar with a changing mugshot showing your mustache rebirth, it would be an interesting progression or is it too late?

[Jon Wehrenberg]

Bruce, in the upper RH corner of the display it should read "mode" when you are in performance mode. It shows nothing when you are in the default economy mode. I think this is reversed for Tuga's coach.

I wouldn't bet about adding 200 RPM. I think under the exact same pedal pressure it may do that, but I have found I can do a full power acceleration in my coach and wind out each gear to max RPMs something not even close to possible in economy mode.

When you are climbing a steep hill you want the engine wound as tight as possible for maximum HP. I manually downshift to prevent the transmission from upshifting if required.

[bluevost]

Not all modes are created equal. In my CC, when mode is on, I am in economy. When mode is off, I am in performance.

Ken

[0533]

Bruce, in the upper RH corner of the display it should read "mode" when you are in performance mode. It shows nothing when you are in the default economy mode. I think this is reversed for Tuga's coach.

I wouldn't bet about adding 200 RPM. I think under the exact same pedal pressure it may do that, but I have found I can do a full power acceleration in my coach and wind out each gear to max RPMs something not even close to possible in economy mode.

When you are climbing a steep hill you want the engine wound as tight as possible for maximum HP. I manually downshift to prevent the transmission from upshifting if required.
Thanks Jon and Ken for the info. I will make this part of my driving habits from now on. I did learn about keeping my foot on the floor for hill climbing but missed the page on Economy verses performance.

[MangoMike]

Perhaps I mispoke.

Shifting is delayed for an extra 200 rpm. The engine does gain an extra 200.

Mike

[Jon Wehrenberg]

Ken brings up an excellent point.

For our coaches the default mode was economy. It has smoother shifts and delivers the best fuel mileage at the expense of some hill climbing ability if left to shift on its own.

Prevost cannot change the default. Ken's coach was either ordered with the transmission set to use performance mode as the default, or an Allison dealer reset the default. Allison dealers are the only folks who can change the default mode.

This according to Bill Jensen of Prevost.

[Coloradobus]

Well, everyone drives differently. We use the "mode" button most of the time, with and without the cruise control.
When we were east a few years ago on the piedmont, I let the coach run in "economy." All other times, the mode "sport" button is on.
We have put 50,000 miles on this coach in 3 1/2 years, and the bulk of this mileage has been done with the transmission in "Sport: mode.
When we were running with "Orange County Gang" last April to Kerrville, we had a "RPM Check" Everyone but us was running around 1450 rpm at 62 mph in 6th gear. We were at 1800 rpm is 5th. If we are going less than 68 mph, our tranny is in 5th gear.
So, everyone's preference is different for various reason. Our mileage useage is not significantly different whether in Sport or Economy>:D

[Jon Wehrenberg]

Within certain limits the gear a bus is in and the RPM are not an absolute indicator of horsepower produced or fuel consumed.

The fuel we consume is directly proportional to the HP produced. If we lug a coach up a hill in a higher gear at a given speed we are likely to consume the same amount of fuel as a free revving engine going up the same hill at the same speed in a lower gear. As Jim and Chris point out their use of a lower gear does not impact their fuel mileage appreciably.

There is an engine operating range in which the engine is producing near maximum HP and torque. Above or below that range of RPM you give up either mileage or pulling power.

[dale farley]

I've noticed that my RPMs will sometimes go to 2200 if my Jake is in the "High" setting and I let off on the accelerator. Is this unusual or damaging?

[Jon Wehrenberg]

That is good Dale.

A jake works best at higher RPM, and your DDEC is controlling things to optimize your engine, transmission and Jake combination.

[jonnie]

Dale,

Jon is correct as usual. Just don't make a habit of overspeeding your engine when applying the Jake Brake. Understand what your maximum RPM rating is and keep at or under that point.

[Coloradobus]

Forget to say above, if we go up a hill in 3rd, we down the other side in 2nd with full jake. If the jake will hold the coach back in 3rd, I would use that..

[bwalz]

Made it to Richfield, UT on I-80 most of the way with no problems. It did help to switch modes to avoid shifting to a "dead" gear.
The only temperature problem was 19 degrees this morning and snow! Hopefully Cedar City and Virgin, UT will be better.

[lewpopp]

Bwaltz,

You mean they told you how to climb some of those mountains and never told you how to deal with the cold?

[bwalz]

Thanks to the "Aqua Hot gods" we stayed warm. I still need to figure out the block heater though.