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-   -   On towing at high elavation. (http://www.airforums.com/forums/f238/on-towing-at-high-elavation-23722.html)

Boondocker 06-20-2006 08:06 AM

On towing at high elavation.
 
Say you have a tow vehicle (1991 f150, 5 speed manual, 302) that is getting older, maybe using some oil but not a lot, and are towing an Airstream (4,000 lb dry)that is closer the upper end of the TVs rating than the lower end. You pull fine on the flats with some slowing on rolling hills (say 5-8 mph). You normally tow at 55 and are not prone to getting anywhere in a hurry, cars passing do not give you ulcers.

Now say to this point, with this Airstream, all the towing has been done in the Midwest, both on the plains and in hill country (yes, there are in fact have hilly country in the south parts of Illinois and Indiana). However, with this same TV you have towed in the Rockies on several occasions. On those occasions you have towed a Jayco Popup that weighs something like 1,500lbs dry. The popup drew down gas mileage by a couple mpg and you noticed it was there on hills (using overdrive [yes, now I know better]) but did not significantly impact driving.

So here is where this is headed: provided that a guy didn’t get in a hurry on the long grades, is this TV likely to do ok with the Airstream at elevation? Or conversely, would the elevation just add to much challenge? Part of me thinks that the larger surface area would be an issue, while another part of me says that if you are going 45-50 mph on that climb the impact on towing from resistance ought to be significantly reduced. This makes me think that the real question is, with air resistance aside, would the increased elevation paired with the extra weight, result in reduced power to the point of making the operation a no-go. I was just curious what the motor heads think about this and what other issues might come into play that I haven’t thought of.

Boondocker 06-20-2006 08:41 AM

Deduct 2% per 1,000ft?
 
Elevation related loss of performance: “Since gasoline engines lose power at a rate of three percent to four percent per 1,000 ft. elevation,” (above mean sea level) “a reduction in gross vehicle weights and gross combination weights of two percent per 1,000 ft. elevation is recommended to maintain performance.” (Source: Ford Motor Company 2001 RV & Trailer Towing Guide, North American Fleet, Lease and Remarketing Operations, Copyright August 2000.)


This sound about right?

silverback 06-20-2006 08:46 AM

So at 7K feet (not an uncommon pass elevation out west) you would need a weight reduction of 14% per Ford's guideline. That sounds like a healthy chunk to take out especially if you're already running dry tanks.
-KL

dwightdi 06-20-2006 09:49 AM

Not only the reduced power but the cooling capacity of the trans oil and coolant radiators mean you will be stressng the rig to the max. Any weakness in the rods and main bearings or transmission will be trouble for you on the road. Have the TV gone over by a pro and brought into top condition and change all the fluids before you attempt it. Also the brake fluid will be tested to the max. Any absorbed moisture over the time will cause the brake fluid to boil and you will lose all braking capacity (I had it happen to me. Very scarey) You must purge all old brake fluid out of the TV and replace with new stuff before you attempt this journey.

Boondocker 06-20-2006 09:57 AM

Good point
 
Good point, I am pretty diligent about that sort of maintance prior to trips. I am also fortunate to have a beefed up radator. It has also occured to me while googleing away that the simple switch to non-ethanol gas would be a big boost alone (I am reading it degrades effeciency by 10%). Theoretically, that would hold me even power wise for an additional 5,000 ft (I think). Am I misguided on that thought? I think I may try some premium in the tank just to test the effect of no ethanol.

InsideOut 06-20-2006 10:05 AM

I'm not a motor-head, but I know we tune up our engines slightly differently here for high-altitude driving. There is less oxygen so things are opened up more (non-motor-head-speak). When we first moved here (from sea-level) our vehicles lugged & chugged but once they were gone over locally they were fine. Not sure it's worth doing on either end of a short trip, but I know it makes a difference, especially in the mountains. Denver is 5,280 but some passes are up over 11,000, some with 5-7% grades. Needless to say, you braking equipment needs to be top-notch as well. In less than an hour from home, I can be at over 11,000 feet ~

FWIW, when we started towing, it was with a Jeep Cherokee. We were well within the stated towing capacities of the Jeep (5000 lbs, our trailer is at about 3400). We always towed dry, lightly loaded and slowly. We struggled & overheated every time we went up the mountain. We now have a '96 Yukon V8 5.7L and we do fine on premium (when towing) gas.

Shari :flowers:

AZstreamin 06-20-2006 10:23 AM

Hey Rodney,
Everyone has made good points the one that I must echo is the Cooling System. It will be critical that it is in top condition. Where you plan on traveling in the West will make a difference, in AZ, NM, UT, NV parts of CA and CO it is not uncommon to tow in the mountains with 5-7% grade and have 95-100 degree heat this multiplies all possible problems.
AZstreamin

uwe 06-20-2006 12:15 PM

Rodney,
You will loose a hefty amount of engine power once at altitude. You will be slow cresting the highest passes. You will have to watch your engine temperature, and use good judgement on how quickly you want to get to the top. You will also have to remember to go down slowly on the other side. Your manual trans might be of advantage going downhill, but I have never towed with one myself.
But most importantly, if you use common sense, and don't overtax your equipment, you will be fine. I went over Colorado's Wolf Creek pass a few years ago, some 10000+ feet if I remember right, towing my 6000lb TradeWind, and it was slow going, getting slower with altitude. I passed some very slow underreated tow rigs on turnouts, only to be passed again by them when I took a rest at the top....
Allow plenty of time, let the faster guys pass you, ( use turnouts) and enjoy the trip. Sure, a new Diesels would take you over the passes a bit quicker and safer, but your reality is different from that, so you simply need to adjust to it and take your time. Chances are that yoour trailer was towed by much smaller vehicles over the same passes in it's former life...

Paul Mayeux 06-20-2006 04:38 PM

Quote:

Originally Posted by Gen Disarray
Elevation related loss of performance: “Since gasoline engines lose power at a rate of three percent to four percent per 1,000 ft. elevation,” (above mean sea level) “a reduction in gross vehicle weights and gross combination weights of two percent per 1,000 ft. elevation is recommended to maintain performance.” (Source: Ford Motor Company 2001 RV & Trailer Towing Guide, North American Fleet, Lease and Remarketing Operations, Copyright August 2000.)


This sound about right?

This sounds about right. It's what I've read in the Ford manual and it states the same thing in the owners manual of my Honda Ridgeline. I saw somewhere that at about 10,000 ft of elevation you only have about 75% of the oxygen that there is at sea level. Also, you mentioned ethanol fuel and it's impact, the octane requirements decrease as you increase in altitude. Octane ratings at the pump in the higher elevations like in Colorado are typically less than in the lower elevations like here in Texas. I've seen some in Colorado in the past as low as 82, and when I ran it the motor didn't seem any more prone to detonation than using 87 in Texas.

scottanlily 06-21-2006 12:01 AM

In the higher elevations the engine does not require the octane amounts to control pinging ,poor combustion etc as at sea level or lower elevations.The engine however loves more ignition timing at high elevations and that helps the power.I won't repeat all the good advice all have already given ,they are of course correct ,marginal now ,a struggle indeed at high elevations as you may feel you may not get up the pass .

Scott

genearnold 06-22-2006 10:40 AM

I towed my old '69 International 31' over Monarch Pass several times, as well as once over Rabbit Ears, and assorted lower pulls with two vehicles, a '79 GMC with a 350 ci automatic and an '83 Chevy 6.2 diesel (no turbo charger) with an automatic. I made it without trouble but sloooow!

I pulled my 34' Limited through Jackson, Wyoming once with a '94 Chevy, 5.7L that had almost 200,000 miles on it. In each of these trucks I had a heavy duty transmission cooler installed in addition to whatever cooler came with the factory trailer tow package.

As important as is the engine power, of equal importance is gear ratio. The GMC and Chevy 5.7 had 3.73s and the Chevy diesel had a 4.11 (as does my present Dodge Ram diesel 5 speed).

Gene

2airishuman 06-22-2006 06:13 PM

hi rodney

all of the above is good thinkin'

ya like an adventure don't ya?

taking flatland rigs to the mountains invariably finds the weakness..
and makes them more apparent...especially in 'vintage tv units'

don't worry about wind resistance...you won't be going that fast uphill.
and the air is too thin to slow ya much going down!!!

you will be lucky to keep it about 35mph on the higher passes....and that might include a stop or 2...for cooling.

coming down again 50 will seem like 100 so think slow.......
turn on the flashers....i do.

carry motor oil.....
carry diluted antifreeze.....
carry brake fluid.....
carry a credit card.....

hopefully you won't need any of these things....

make sure your brakes are ready....pads? also the trailer brakes..shoes?
the tranny can save the brakes somewhat but ya can cook the tranny too...

my most significant rv breakdown/delay was just at the entry to the tunnel near vail.....where stopping is FORBIDDEN, and breakdowns get squashed by the semis.....it's a long story.....but the airstream and i both survived.....

summer heat AND altitude will test ya but what the heck....go for it.

the long grades are taxing combined with altitiudes about 4-5k feet....but i love it up there!!!

cheers
2air'

silverback 06-22-2006 07:22 PM

And by the way it's getting hot out here
 
So not only will you be going real slow you will most likely be doing it without the AC on. Of course above 6000 feet it cools off but can still be in the 90s. I would also think about changing the rear diff fluid to the synthetic flavor.
-KL

azflycaster 06-22-2006 08:42 PM

Here is a high elavation question
 
The highest I have ever driven was a little over 14,000 feet. It was a good thing I did not have a trailer behind me. The air was thin, it was COLD (snow on the ground) and it was the 1st of July, 3 days befoe the big race. Where was I?


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