Community Forums

jayhawk1 · 06-21-2010, 02:52 PM

Next month I will be going through Colorado. Since this will be in July and hot, I was wondering if anyone had any tips on gears and rpms to keep the engine from getting hot.
I have a 2005 Mountain aire 4304 with a 400 cummings/Allison.
Thanks. Bob

Chuck 1935 · 06-21-2010, 03:03 PM

Your best bet is to gear down and keep the RPMs close to the redline to keep the strain off the engine. Keep an eye on the temperature guage. It will get hotter but should not get into the red, if it starts creeping up there, drop down a gear. The air is generally cooler at the upper altitudes which helps.
Before you leave, be sure to clean out the fins of your radiator so that you can get the most air through it that you can. It will be a wonderful trip!

mythplaced · 06-21-2010, 03:18 PM

keep above 1300 (max torque) and less than 1900 and you should have no cooling issues...At least I dont....

jayhawk1 · 06-21-2010, 03:19 PM

Thanks for the response. The reason I was a little worried was because I went through needles California last August when it was 117 degrees outside and it got hot enough for the engine and transmission alarms both to come on.
I realize The Rockies will be a lot cooler than Needles but I will also be climbing higher.

Always-RVing · 06-21-2010, 03:40 PM

Your 400 Cummins will have a power-band to maximize the engine's performance at a given RPM. You should not be anywhere near the RPM REDLINE..

The sweet spot for your motor can be found from Cummins which is based upon the motor model. Mine is around 1850 RPM's at 65 mph for optimum power output to cruise. As you know, Diesel engine max power output in horsepower and torque are generally low RPMs where gas engines are high RPMs. Your engine will deliver a power out rating at some given RPM curve. At the peak of the curve, it will be doing all it can. While climbing hills, try to maintain maximum power output and engine temp as cool as you can and below say 220 degrees max and not in the temp red zone. Whatever speed you end up with is all she'll do. Some hills I'm climbing at 55 mph (5th gear) while others, I'm at 35 or 45 mph (4th gear). While some still, I'm at 20-25 mph (3rd gear). It all depends upon the engine's performance capacity and load. One other thing, as you climb, you'll lose power ability.

400 hp Cummins is the 8.9 ISL. A very nice motor. http://www.everytime.cummins.com/assets/pdf/4971107.pdf

Horsepower is a calculated value from torque which is what moves you.

While climbing, drive the tach for optimum power output at your engine's peak power curve which is between 1500-1800

Dav5942 · 06-21-2010, 08:25 PM

Don't know why you have overheating problems-transmission or engine. Something problably wrong if you do. Have traveled from Mexico to Alaska 60k miles, 120 degrees outside to 10+ grades-no overheating problems. I let the cruise control decide the gears and have never manually downshifted-no problems with our ISL.

clubmed98 · 06-21-2010, 09:05 PM

my 98 DSDP and present rig never have had heat issue so i would agree a cooling system check needed...having said that on long hard climbs i try and find the gear that will allow the coach to stay between the torgue and hp rpms..on basic hills just mash it..

jayhawk1 · 06-22-2010, 12:33 PM

I think what happened was ,I had just picked this coach up in Las Vegas and was not familar with it yet. I never shifted it down and was probably lugging it. I have never had any over heating problems since.
I do not remember for sure but it could have been in overdrive. It seemed as though it would not shift down by using the arrow down button. Since then I have shifted it down manually.

Lug_Nut · 06-22-2010, 06:11 PM

This link may be of interest to you. Mountain Driving Challenges Part 1 Grade Speed Control
Additionally take a look at Part 2. A link can be found below the article in red.
Have a nice trip.

Peter