Okay, I've been looking at my 2013 F450 manuals and feeling like a flusterated dinosaur. I can't find anything about the maximum rpm ratings, either in the basic manual or in the diesel supplement. Anybody out there in RV dream land know the maximum SAFE rpm while engine-braking down long monster grades?
cherylbrv said
02:22 PM May 3, 2015
Ditto here. Couldn't find anything in the manuals. Also what is the recommended rpm for going up a monster grade?
Jim01 said
03:28 PM May 3, 2015
Look at your tachometer and if there's a red mark on it, stay a little below that and you should be safe. Most tach's have a "red line" of some type.
Jim
Trikester said
04:07 PM May 3, 2015
No red mark. Not one of Ford's better ideas. On the NuWa forum I got the following response from Greg Surratt:
"I found the same chart - zero hp and torque at 3700 rpm for all years of the 6.7L Powerstroke, max at 2800 rpm.
"My practice is to try to hold the engine around 2800 -3000 rpm and never more than 3200 rpm when descending a hill.
"If I slow down enough at the top of the hill, I can go most of the way down without touching the service brakes by forcing the transmission into a lower gear. I usually descend at the speed posted for the big rigs. My combined weight is over 31,000 lbs."
My combined weight is about 29,000 lbs., and Greg, for practical purposes, has the same truck I do, a 2011 F450 6.7L. So, this should apply.
MarkS said
05:28 PM May 3, 2015
Exhaust and jake brakes work best at higher RPM. I don't know about your little engines but I would assume that once you find the red line you could run it up to red line without concern. When descending a hill find the gear that, while using the exhaust brake, will maintain a safe speed without touching the brakes. This is likely to be near red line depending on how steep the hill is and how much brake horsepower your brake engine combination develops.
Not all trucks are the same. For example, a 14L Mercedes/Detroit engine has a jake that doesn't work very well at certain speed/gear combinations. My 15L Cummins will stop if I have the jake set too high, especially towing 20k pounds or less or a GCVW of less than 40K pounds. The heavier I am or the more severe the grade the closer I must run to red line which for me is about 2100 RPM. Under normal driving conditions I prefer to keep my RPMs below 1500.
Bill and Linda said
01:06 PM May 5, 2015
I wish I could verify the max RPM for your engine in the engine braking mode.Believe me I have hunted ever since a good friend literally had his Ford 6.0L engine blow up due to over revving during braking; at least according to Ford and the diagnostics from the computer. The Ford’s “computer” is not supposed to allow this – but it happened nonetheless.
Picking up on Mark’s comments – Yes the “little” diesels are different.The GM / Chevy Duramax has a powered red line of 3,200 RPM it won’t go over – it will up shift at 3.200 RPM under power.But it has a “braking” red line (no fuel applied) of 4,800.No, that’s not a typo - 4,800.GM used to put a yellow and a red line on the tack, yellow for powered RPM and red for braking RPM. They took them off because the yellow confused some.But it is 4,800 and I’ve been to 4,400 RPM many times without issues coming down mountains and it, along with the OEM turbo brake, does a very fine job.
A suggestion:Put your truck in tow haul and drive it without the trailer.Use maximum acceleration and determine where it up shifts – at what RPM the computer commands an up shift to the next gear.Whatever that RPM number is under load that’s the braking RPM I would not exceed until I knew for a fact it was OK to exceed that number on your particular engine.There are a lot of different Ford diesels from over the years.A lot of this has to do with what is called “valve float” and some of the engines just can take high RPM even when “coasting.”
Howard "consulted" with them a bit as I recall when he had to replace his engine - earlier model than yours. But nonetheless these are Ford diesel experts and perhaps they have some solid info that might be useful. If they do, please post it for all to know. Thanks.
Bill
-- Edited by Bill and Linda on Tuesday 5th of May 2015 01:21:47 PM
TRAILERKING said
01:23 PM May 5, 2015
Yes I don't like how my 8.3 Cummins just buzzes when it drops from 6th to 4th when the exhaust brake is applied. However the engine RPM has to be higher for the exhaust brake to be effective. If the RPM is a lot lower there is barely a noticeable difference in engine braking. However all units are a bit different depending on the programming.
MarkS said
09:54 AM May 6, 2015
Just like there are torque and horsepower curves there are similar curves for exhaust and Jacobs brakes. Neither one works at very low RPM. The engine has to be spinning fast enough to generate the necessary back pressure or vacuum for the engine brake to have the desired effect.
lmcallis said
12:16 PM May 6, 2015
I'll throw in my two cents, if no likes em, just leave em on the ground.
I pull our 17000lbs 5th wheel with a 2007 ford 1 ton 6 liter diesel. Going up hill I treat it like a farm tractor, give it all the throttle it wants but never let the RPM's go over 2500 rpms. It can climb all day at that RPM and the oil temp monitor stays below 235 degrees. Well, I'd probably pull over and give it a rest after a while, but so far in 8 years I've not had to.
Going down hill, I don't let the rpm's go above 3700. Where did that number come from.....I learned it from the Arizona smog test procedure. During the smog test, you put the transmission in neutral, foot on the brake, and floor the engine. On my ford, the governor kicks in at 4000 rpms and won't let the RPMs go above that. Chevy and Dodge, and newer Fords likely have different settings but Arizona does the smog test the same way so without a mark on the tachometer, it is a good way to find out what your engine's max RPM limit is.
However, a governor (or computers) can't do a thing to hold back engine RPM's going down hill after using up all the lower gears in the transmission or the exhaust brake. So, going down hill, with 17000 lbs behind pushing on the truck, the engine is out of options if the tranny/exhaust break can't hold the RPM's under 4000 and you're not putting your foot on the brake to slow down. The only option the engine has is to throw a rod or piston and we know where that take you.
For a little safety, and since my truck doesn't have an exhaust brake, I backed the 4000 max RPM's down to 3700 rpms. Once I hit that, I've got to use the brakes to save the engine from tearing itself apart. Also, without an exhaust brake, I start down the hill in the lowest gear I'm going to use, as Tow/Haul can't downshift to a lower gear if the rpms are already above the max rpm for that next lower gear. So I manually set the transmission in 2nd for a 5% grade or 1st for anything above 5%.
Yep, you've probably seen me out there. I'm the 5th wheel out there in the right lane, crawling down the steep grade with my flashers on. Good luck out there,
Lance
MarkS said
02:22 PM May 6, 2015
Yep, you've probably seen me out there. I'm the 5th wheel out there in the right lane, crawling down the steep grade with my flashers on. Good luck out there,
Lance
You can go down the hill hundreds of times too slow but only once too fast.
TRAILERKING said
02:45 PM May 6, 2015
MarkS wrote:
You can go down the hill hundreds of times too slow but only once too fast.
Damn................Another good one.
That'd be a good one to display on the back of the rig...
Camper_Boy said
03:26 PM May 6, 2015
I try and slow as I crest the mountain to let tow haul manage speed. Other than that I use my trailer brakes to slow down. My toy hauler has electric over hydraulic disc brakes which slow whole 30,000lbs GCWR. Last time I had Mor/ryde check my rig...they said brakes were as new, so don't be afraid just to brake...I usually don't like to hit 3000RPM's only in short doses, before applying brakes.
Good luck and bring them home alive...
Bill and Linda said
03:22 PM May 7, 2015
Camper_Boy wrote:
I try and slow as I crest the mountain to let tow haul manage speed. Other than that I use my trailer brakes to slow down. My toy hauler has electric over hydraulic disc brakes which slow whole 30,000lbs GCWR. Last time I had Mor/ryde check my rig...they said brakes were as new, so don't be afraid just to brake...I usually don't like to hit 3000RPM's only in short doses, before applying brakes.
Looking forward to seeing you guys in a couple of weeks at the reunion in Marion.Last time was Camp MOR/ryde as I recall.
Bill and Linda
Camr said
11:24 PM Jun 29, 2015
A rule of thumb from my OTR truck driving days was to plan to go downhill at the same speed as you would climb the hill. That rule got me through 2.5 million miles without a safety issue.
Trabuco said
08:40 AM Jun 30, 2015
I surprised you can't get engine parameter information from Ford. I called cummins on my ISL 400 and they gave me everything you can think from over speed to temperature shutdown and of course the all important sweet spot.
I have have all the info I need based on the cummins engine that was installed in my coach. They track the application of their engines by VIN number.
Okay, I've been looking at my 2013 F450 manuals and feeling like a flusterated dinosaur. I can't find anything about the maximum rpm ratings, either in the basic manual or in the diesel supplement. Anybody out there in RV dream land know the maximum SAFE rpm while engine-braking down long monster grades?
Look at your tachometer and if there's a red mark on it, stay a little below that and you should be safe. Most tach's have a "red line" of some type.
Jim
"I found the same chart - zero hp and torque at 3700 rpm for all years of the 6.7L Powerstroke, max at 2800 rpm.
"My practice is to try to hold the engine around 2800 -3000 rpm and never more than 3200 rpm when descending a hill.
"If I slow down enough at the top of the hill, I can go most of the way down without touching the service brakes by forcing the transmission into a lower gear. I usually descend at the speed posted for the big rigs. My combined weight is over 31,000 lbs."
My combined weight is about 29,000 lbs., and Greg, for practical purposes, has the same truck I do, a 2011 F450 6.7L. So, this should apply.
Not all trucks are the same. For example, a 14L Mercedes/Detroit engine has a jake that doesn't work very well at certain speed/gear combinations. My 15L Cummins will stop if I have the jake set too high, especially towing 20k pounds or less or a GCVW of less than 40K pounds. The heavier I am or the more severe the grade the closer I must run to red line which for me is about 2100 RPM. Under normal driving conditions I prefer to keep my RPMs below 1500.
I wish I could verify the max RPM for your engine in the engine braking mode. Believe me I have hunted ever since a good friend literally had his Ford 6.0L engine blow up due to over revving during braking; at least according to Ford and the diagnostics from the computer. The Ford’s “computer” is not supposed to allow this – but it happened nonetheless.
Picking up on Mark’s comments – Yes the “little” diesels are different. The GM / Chevy Duramax has a powered red line of 3,200 RPM it won’t go over – it will up shift at 3.200 RPM under power. But it has a “braking” red line (no fuel applied) of 4,800. No, that’s not a typo - 4,800. GM used to put a yellow and a red line on the tack, yellow for powered RPM and red for braking RPM. They took them off because the yellow confused some. But it is 4,800 and I’ve been to 4,400 RPM many times without issues coming down mountains and it, along with the OEM turbo brake, does a very fine job.
A suggestion: Put your truck in tow haul and drive it without the trailer. Use maximum acceleration and determine where it up shifts – at what RPM the computer commands an up shift to the next gear. Whatever that RPM number is under load that’s the braking RPM I would not exceed until I knew for a fact it was OK to exceed that number on your particular engine. There are a lot of different Ford diesels from over the years. A lot of this has to do with what is called “valve float” and some of the engines just can take high RPM even when “coasting.”
FWIS
On edit: May I suggest you call these guys:
http://powerstrokehelp.com/
Howard "consulted" with them a bit as I recall when he had to replace his engine - earlier model than yours. But nonetheless these are Ford diesel experts and perhaps they have some solid info that might be useful. If they do, please post it for all to know. Thanks.
Bill
-- Edited by Bill and Linda on Tuesday 5th of May 2015 01:21:47 PM
I'll throw in my two cents, if no likes em, just leave em on the ground.
I pull our 17000lbs 5th wheel with a 2007 ford 1 ton 6 liter diesel. Going up hill I treat it like a farm tractor, give it all the throttle it wants but never let the RPM's go over 2500 rpms. It can climb all day at that RPM and the oil temp monitor stays below 235 degrees. Well, I'd probably pull over and give it a rest after a while, but so far in 8 years I've not had to.
Going down hill, I don't let the rpm's go above 3700. Where did that number come from.....I learned it from the Arizona smog test procedure. During the smog test, you put the transmission in neutral, foot on the brake, and floor the engine. On my ford, the governor kicks in at 4000 rpms and won't let the RPMs go above that. Chevy and Dodge, and newer Fords likely have different settings but Arizona does the smog test the same way so without a mark on the tachometer, it is a good way to find out what your engine's max RPM limit is.
However, a governor (or computers) can't do a thing to hold back engine RPM's going down hill after using up all the lower gears in the transmission or the exhaust brake. So, going down hill, with 17000 lbs behind pushing on the truck, the engine is out of options if the tranny/exhaust break can't hold the RPM's under 4000 and you're not putting your foot on the brake to slow down. The only option the engine has is to throw a rod or piston and we know where that take you.
For a little safety, and since my truck doesn't have an exhaust brake, I backed the 4000 max RPM's down to 3700 rpms. Once I hit that, I've got to use the brakes to save the engine from tearing itself apart. Also, without an exhaust brake, I start down the hill in the lowest gear I'm going to use, as Tow/Haul can't downshift to a lower gear if the rpms are already above the max rpm for that next lower gear. So I manually set the transmission in 2nd for a 5% grade or 1st for anything above 5%.
Yep, you've probably seen me out there. I'm the 5th wheel out there in the right lane, crawling down the steep grade with my flashers on. Good luck out there,
Lance
You can go down the hill hundreds of times too slow but only once too fast.
Damn................Another good one.
That'd be a good one to display on the back of the rig...
Good luck and bring them home alive...
Looking forward to seeing you guys in a couple of weeks at the reunion in Marion. Last time was Camp MOR/ryde as I recall.
Bill and Linda
I have have all the info I need based on the cummins engine that was installed in my coach. They track the application of their engines by VIN number.