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Deep descents, rpms, redline, etc.

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PJ Corey

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Deep descents, rpms, redline, etc.
« on: September 30, 2010, 10:10:30 am »
I recently drove Rt. 4 in New Mexico from Cuba in the Jemez Mountains down to Bandalier National Monument.  I went from 11,500 plus feet to about 5,000 feet on a steep and curvy mountain road with 10 mph hairpin turns that nearly burned my brakes out.  I won't be doing that route again in my rv! 

Question:  what are the "best practices" in downhill descents such as this, aside from avoiding them?  What are rules of thumb regarding rpms on such a descent? What is the red line on the E450? Can't find anything online in reference to the E450.   Thanks.

Paula
Santa Fe
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Ron Dittmer

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Re: Deep descents, rpms, redline, etc.
« Reply #1 on: September 30, 2010, 12:04:22 pm »
3 years ago with our first tow vehicle without secondary braking, we had a similar experience exiting Yoemite NP's NE area.  Short of riding the brakes, it was uncomfortable.  The name of the game is to go slow, pump brakes, you know the usual drill.

Given there is no red zone on the tachometer, I assume red-lining is when the RPM needle is pegged.  With 5w-20 full synthetic oil in the engine (per owners manual) I don't worry about RPMs unless it pegs.  Mind you my engine RPM never did get that high.  Just uncomfortably close.
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lghjr

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Re: Deep descents, rpms, redline, etc.
« Reply #2 on: October 01, 2010, 08:31:01 pm »
My opinion only, but I would play the gear game to use the engine braking as much as possible.  Correct mountain driving if I remember correctly is to slow well below what is required and as speed builds again, brake again.  That should give adequate cooling in between brake applications.  I lost the brakes going into Red River NM once pulling a trailer and it not only get's your attention but causes one to seek the best info so it does not happen again(Ford F-250 diesel).  I have done Bobcat pass several times since with out problems by getting into a low gear at the top and judiciously slowing/braking.

L. G.

 
 
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Ron Dittmer

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Re: Deep descents, rpms, redline, etc.
« Reply #3 on: October 01, 2010, 09:17:26 pm »
We do play the gear game, but it's still a challenge, especially considering the tow vehicle.
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TomHanlon

Re: Deep descents, rpms, redline, etc.
« Reply #4 on: October 02, 2010, 08:53:48 am »
I will play both games. I figure with todays engines and transmissions, they will not let me do them any real harm, but the brakes can very quickly over heat. So when starting down a steep hill, I will slow down and select a lower gear and sometimes I will turn on the tow/haul mode. If my speed continues to build and jabbing the brakes does not keep me from speeding, the tow/haul will down shift for me and slow my speed. If the engine starts to exceed the red line, the tow/haul will up shift and it is up to me to slow her down using the brakes. Just my way of driving.
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mciai2000

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Re: Deep descents, rpms, redline, etc.
« Reply #5 on: October 03, 2010, 08:48:21 pm »
Happy Fall:

When we were coming down the mountains in Maine this summer, I did exactly what Tom did.  In fact, I kept the mh in tow/haul mode the entire time.  What a great piece of engineering that is. It works just like Tom said.  I do have secondary braking in my toad. 

DJM
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bigbadjc

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Re: Deep descents, rpms, redline, etc.
« Reply #6 on: October 07, 2010, 02:07:20 pm »
I have a 2006 PC 2551 with the F350 chassis and just finished a 5000 mile trip up to the Canadian Rockies and crossing over them into BC.  Like the last two respondees, I used the Tow/Haul option the whole time I was in mountainous country and it worked beautifully.  When I first started out in Arkansas, I had one bout of smelly brakes and pulling to the left before I decided to go the Tow/Haul route when I got to more serious moutains.  After that, I had no problems with having to use the brakes too much to maintain the proper speed on downhills or downshifting as needed to maintain a good rate of climb going uphill.  As I understand it from the manual, Ford uses some adaptive learning circuitry to see what you're trying to do re speed and adjusts its shifting accordingly.  This is so much better than an older Ford V-10 I had in a BT Cruiser that merely had an overdrive off/on switch on the shift lever. Considering that no red line is shown on the tach or mentioned in the manual, I would no worry about the 4-5K RPM speeds reached using this device.
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mciai2000

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Re: Deep descents, rpms, redline, etc.
« Reply #7 on: October 07, 2010, 09:15:55 pm »
I agree with bigbadjc.  In fact, when I am pulling my toad, I use tow/haul mode from the time I leave my driveway until the time I come home again.  I tried using both ways and I find it does not have an effect on gas milage either way.  I actually think going up to Maine I had better gas milage with tow/haul mode on.  Now, that is great American engineering at its best.

DJM
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