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Old 11-11-2009, 02:58 PM   #1
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Question on RPMs and 'redlining'

My unit sits on a Ford Chassis with a V-10 Vortec engine with auto-transmission. Does anyone know what the 'redline' rpms are
for the V-10 engine.
We were recently going through Steamboat Springs, Colo. and came down a very long, steep grade. I put the transmission into low and let the unit
slowly take me down. The transmission was really whining.
I happened to stop in at a local Ford dealership and the service manager said
that 'it is impossible for the engine to redline in first gear while
coasting downhill! He stated that the only way to redline the engine
was to hold down the accelerator until the engine built up too many rpms."
Is this true?
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Old 11-11-2009, 06:30 PM   #2
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We have the V10 too in our rig and this was our first experience with the Ford chassis and engine. While descending a pass using tow/haul mode and our Jeep in tow it ran upwards of 5000 rpms which sounded and seemed very high. However I have also noticed it's propensity to kick down on mountain passes and revving just as high when pulling up the grade. While it does seem disconcerting to the ear it never the less is the way it was engineered and therefore should present no problems. I have never yet seen the water or transmission temperature gauges do anything other than stay pegged in the middle even in the heat of Arizona either. I also don't recall seeing a "red line" on the tach but it tops out at around 7000rmp (I would have to go out and look to be sure). I don't know if there are govenors in place to prevent over-revving on these engines or not, perhaps a Ford expert here could tell us.
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Old 11-11-2009, 08:13 PM   #3
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Google knows all...

http://forums.truckinweb.com/70/6461...v10/index.html

Per the link.. redline = 5250 and at this point the fuel flow is reduced.

Regarding the downshifting, I just use the tow haul mode and let the computer figure it out. Well that and the US Gear UTB that I have on my Saturn. In more serious braking, that Saturn gives me a tug.. It's a very nice feeling when your trying to stop.
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Old 11-11-2009, 09:48 PM   #4
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This day of computer controlled engines, there isn't a "REDLINE". The computer is in control, and there is a "rev limiter" that will kick in when max rpms are obtained. You can go out, start your vehicle, hold the throttle flat on the floor and not hurt anything. The computer would control spark and fuel and you would here the engine starting miss fire, and do what is called "bounce" off the rev limiter.
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Old 11-14-2009, 12:28 AM   #5
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'Redlining follow-up'

Thanks for the responses...but...

One responder mentioned his tack was running at 5000 RPM, another
mentioned an 'electronic redline computer limiter' at 5200 RPM.
A Ford dealer did mention that the engine will limit itself at about 5000 RPM and 'limit' fuel flow to keep the RPMs below 5000.
But these situations are for when the engine is pumping fuel through the injectors.

My Toyota shuts off the injectors when the downhill grade is steep. The engine closes off the fuel and uses compression to help control the speed.

My question really was about downhill 'coasting'...is the engine compression enough to limit the RPMs to less than 5000 if the engine's fuel is essentially shut off...but the grade is so steep that the unit still wants to accelerate?
What happens if I am in low gear going downhill, my foot off the accelerator, and the RPMs exceed 5000? Will the transmission rip itself to pieces?

The Ford service manager could (would?) not tell me what would happen.

If I were in such a situation, do I let the transmission burn out, or the brakes, trying to negotiate a very steep, long grade?
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Old 11-14-2009, 09:47 AM   #6
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Quote:
Originally Posted by tsunami View Post
Thanks for the responses...but...

My question really was about downhill 'coasting'...is the engine compression enough to limit the RPMs to less than 5000 if the engine's fuel is essentially shut off...but the grade is so steep that the unit still wants to accelerate?
What happens if I am in low gear going downhill, my foot off the accelerator, and the RPMs exceed 5000? Will the transmission rip itself to pieces?

The Ford service manager could (would?) not tell me what would happen.

If I were in such a situation, do I let the transmission burn out, or the brakes, trying to negotiate a very steep, long grade?
Burn out the brakes. The computer will handle the tranny and engine. Your only concern should be for you and the family. Let the tranny and the engine blow/seize/burn/fall out.

If you are actually burning out the brakes, I'm guessing that your coach is WAY overloaded or your brakes need serviced. These systems are designed to handle the GCWR under all reasonable driving conditions, not much more.

Get concerned when you crest a hill and you see dozens of RVs, semis and 5th wheels in a HUGE pile at the bottom. A clear sign of a civil engineer that had a VERY BAD day.
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Old 11-14-2009, 10:59 AM   #7
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Well, you can't compare your Toyota xxxx to your Coach. Too many differences to start to mention. Learn to drive in the mountains if that's where you are going. When your tach reaches 5000, use to the brakes to bring it under 3000, then let off the brakes and let the engine build back to 5000, then the brakes again.
(tach numbers are for reference only and your vehicle may need to operate under different conditions) Don't expect the engine, the trans, or the brakes, to do the WHOLE job. You have many resources you are responsible for as operator, so learn how to use them all together. There are other post on here about mountain driving, search them out and read them, and search other places also. It's not a Toyota, and will require a lot more skill to drive safely.There will be little forgiveness, only a pile at the bottom of the hill.
I apologize if it seems like I'm ranting, I'm not, only trying to keep us all safe while on the highway with each other.
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Old 11-14-2009, 03:39 PM   #8
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The Ford chassis is a great combination. Trust the engineering.

Imagine being in a Semi. manual downshifting, trying to save your air brakes, working the jake brake, trying to remember what your load is today.. We have it easy with the Ford F53 chassis.

I ALWAYS run mine in Tow Haul mode. It's designed for towing and for hauling heavy loads.. Well I'm always hauling a HEAVY load... It's a 38 foot RV!

So keep the speed reasonable before you crest the hill, have tow/haul on and use your brakes. The computer will do the rest.

Just to be extra safe I spent a little extra on my TOAD braking system. Went the with Unified Tow Brake from US Gear. With my Saturn attached, I have 10 wheels of proportional full POWER braking. I stop much easier / shorter with the TOAD than without out.

Feels nice going down a steep incline, stop sign getting closer and closer and then you feel the Saturn tug you backwards
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Old 11-15-2009, 01:18 PM   #9
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Additional info...

My Sunseeker has a Ford E450 chassis rated at 20,000 lbs.
I have weighed my unit (wet) on a truck scale: 15,000 lbs. So my unit
is actually underweight by about 2 1/2 tons.
When I bought my unit, I knew that the unit weighed much less
than its max. vehicle chassis weight limit.
The Steamboat Springs downgrade is about 7% for about 7 miles (2500ft/36000ft).
I had assumed that using a V-10 engine on an 'underweight' chassis
would give me a significant lee-way on steep downgrades via engine
compression. I was surprised that the engine could not handle
a 7% grade in low (first) gear...I had to pull over and let the brakes
cool off half way down!
We now map our mountain trips so that we never go down a grade which
exceeds 5%!
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Old 11-15-2009, 01:57 PM   #10
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Wow... That's some grade / distance.

How did you know the engine couldn't handle it? Engine/Trans temps peg the needles?

Did you have Tow/Haul on?

Also if you forced it into 1st gear and you couldn't keep the speed low enough, it may have upshifted to protect the drivetrain.

From what I've read in the chassis manual, I got the impression that I should run with Tow/Haul all the time and leave it in Drive. The computer apparently senses the amount of braking from the pedal and uses that to determine how much engine braking to do.

Sounds like you have zero weight problems, so hopefully there is a way to adjust your approach to avoid issues.
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