Utclmjmpr
Well-known member
It's also far to expensive to allow an overheat.>>>D
Long grades with my 2005 400hp Cummins?
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AStravelers
Well-known member
Something I do when I see I have a long steady climb, say 3% to 7% grade for 2-5 miles: I manually select a gear to match the RPM level for a speed that makes for an easy pull for the transmission and engine (i.e. no overheating). Then I turn on the cruise control and sit back and enjoy the ride for next several minutes.
Some of these long climbs have sections that level out a bit. Leaving the computer to make the decisions can mean it will upshift and when the climb steepens again it will be slow to downshift, allowing the engine/transmission heat to climb. I can feel and hear the engine starting to labor and the RPM's drop before the downshift occurs.
I always grumbled about the Ford 5 speed with the V10, because it would not let me select 4th gear. You could only manually select 5th or 3rd gear. Only the computer could select 4th. Yes, I could make the computer select 4th by pressing on the accelerator until it downshifted, but then when I eased up on the gas a little too much or the hill leveled out it would jump back into 5th.
Some of these long climbs have sections that level out a bit. Leaving the computer to make the decisions can mean it will upshift and when the climb steepens again it will be slow to downshift, allowing the engine/transmission heat to climb. I can feel and hear the engine starting to labor and the RPM's drop before the downshift occurs.
I always grumbled about the Ford 5 speed with the V10, because it would not let me select 4th gear. You could only manually select 5th or 3rd gear. Only the computer could select 4th. Yes, I could make the computer select 4th by pressing on the accelerator until it downshifted, but then when I eased up on the gas a little too much or the hill leveled out it would jump back into 5th.
A Traveler said:
Exactly right for me. I found if I kept the "go" pedal floored not only would my foot get tired on long climbs, the engine temp rose quickly to 225 and the alarm came on. If I shifted manually and "got ahead" as you say, much less chance of overheating ang gettin up the mountain.
AStravelers
Well-known member
rrfpacker said:
Very much my perspective as well.
One thing I do going up hill is to be in a gear, RPM and speed so that I can still be able to press harder on the "go" peddle and possibly increase my speed. Not so much that I actually do increase my speed, but I feel the engine and transmission isn't work as hard if I don't have it to the floor board.
A Traveler
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The reaction time in our coach is MUCH longer than a second or two. As I said in my post, speed will drop from 5 to 10 mph before the transmission shifts down by itself.Gary RV_Wizard said:True enough, but the reaction time is no more than a second or two. And you could get the same anticipation by pushing the accelerator down at the bottom of the hill.
It offends some people to think that a transmission computer can do as good or better job of power management than they can. I don't expect to convince any of that ilk, but maybe the rest will relax and let the computers do the job they were designed for.
I?m not ?offended? by the operation of the engine/transmission computer. In fact, I like what it does about 95% of the time. What ?offends? me is the thought that all you have to do in these large vehicles is to put it in ?D? and drive. These things are NOT cars. You cannot just put them in D and drive without giving some thought to where you are (level ground, upgrade, downgrade) and how to get the best overall performance from your coach. Anticipating an approaching grade by shifting down just as you get into the bottom of the grade is a good driving technique that can get you up the grade at a decent speed without overheating. And the computer cannot do that by itself.
ArdraF
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Larry, yes it's a turbo. In the case cited the drastic drop in speed was definitely caused by keeping the cruise on way too long for the increasing elevation! We did the exact same route the following year but remembered to anticipate the long uphill so took the cruise off and it was just fine. That probably wasn't the best example, but maybe useful as a lesson of the combined effect of both elevation and cruise control. It definitely was starved for fuel! The two different years were like day and night.
ArdraF
ArdraF
WILDEBILL308
Well-known member
Most off my diesel experience is with a smaller 5.9 Cummins. The one thing I did that helped greatly was to properly install a EGT probe and gage. You can't make good decisions without good information.
One of my worst overheating evens was not on a steep hill but on a long gentle hill. I was running along on cruise at about 65-66. On my last coach I had to be doing 65 to get it to shift into 6th gear. I know should be slower. (you know how those smart engineers are that Gary talks about) The problem was the grade was just enough that it could maintain speed by maxing out the accelerator and boost while keeping it locked in 6th. This was lugging the engine and driving up engine, EGT and transmission temps. When the alarms started going off I dropped to 4th and 2500 rpm and things started to cool down. It took a while to figure out what happened. So every time I hear about how smart the engineers are I just smile. Yes they may be smart but they set it up to work to the parameters their bosses tell them. Primarily emissions and economy not power.
Bill
One of my worst overheating evens was not on a steep hill but on a long gentle hill. I was running along on cruise at about 65-66. On my last coach I had to be doing 65 to get it to shift into 6th gear. I know should be slower. (you know how those smart engineers are that Gary talks about) The problem was the grade was just enough that it could maintain speed by maxing out the accelerator and boost while keeping it locked in 6th. This was lugging the engine and driving up engine, EGT and transmission temps. When the alarms started going off I dropped to 4th and 2500 rpm and things started to cool down. It took a while to figure out what happened. So every time I hear about how smart the engineers are I just smile. Yes they may be smart but they set it up to work to the parameters their bosses tell them. Primarily emissions and economy not power.
Bill
Old_Crow
Well-known member
WILDEBILL308 said:
Back in the late 80's I was a heavy line tech at the Chevy dealer in Banning, Ca. It's on I-10, west of Palm Springs.
I-10 westbound at that point is a long gentle hill as you describe. I made my bread and butter for about 4 years by changing engines in motor homes that had left the desert, headed home to L.A. and tried to run with the 80mph car traffic. By the time they got to Banning, they'd be gushing coolant from the exhaust, and I even had one guy get his so hot, the insulation under the dog house caught on fire.
I really think the gentle hills are worse than the hard pulls. At least on a hard pull, most people are watching the gauges.
WILDEBILL308
Well-known member
"I really think the gentle hills are worse than the hard pulls. At least on a hard pull, most people are watching the gauges."
I agree that was an eye opener for me. Just putting along and warnings started going off. We stopped not long after that at a rest area and there was a charter bus in there with overheating problems.
Back to the Ops concerns about flying over hills and steep grades. If you slow down then downshift so you don't lug the engine.
Bill
I agree that was an eye opener for me. Just putting along and warnings started going off. We stopped not long after that at a rest area and there was a charter bus in there with overheating problems.
Back to the Ops concerns about flying over hills and steep grades. If you slow down then downshift so you don't lug the engine.
Bill
Gary RV_Wizard
Site Team
How do you "lug" an automatic? No matter what gear you select with the shifter, it will up or down shift to stay in the engines power band.
Skookum
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Gary RV_Wizard said:
Gary, I'll bet you know, but for those in the back - Lugging is when pressing harder on the pedal doesn't increase engine speed. The ignited fuel mixture in the cylinders has nowhere to go, the piston is moving too slowly to allow the mixture to expand at its normal rate. It exerts really high forces on con rods and bearings, and generates a lot of heat. This is the killer in diesels - the exhaust gases are literally flaming hot, and will start baking the turbo. Not as much of a concern in a gas motorhome, but still important to understand because it still puts a lot of stress on the bottom end and can be mitigated by intervening and selecting an appropriate gear for the load or terrain.
This is where people who set cruise before a grade will see that they lose a lot of speed. The MH tries to hold gears longer than it should and won't downshift to anticipate the climb. The cruise module will floor the pedal until it loses so much speed that it's safe to grab the next gear, even when keeping the pedal floored means it's losing speed and generating all kinds of nasty heat.
Powertrain control modules are generally programmed for efficiency. Pressing all the way down on the pedal should cause it to grab a lower gear, but some of these modules wait way too long IMO or they allow too much pedal before they'll change gears. Or they'll let you do things like drive 65mph in 5th (last) gear with the pedal to the floor on a slight incline where the motorhome isn't increasing speed, and can't grab another gear. The next lowest gear would put the RPM's too high to maintain that speed, especially for those of us with low-redline diesel engines. More modern diesels are able to manage this condition and they will de-fuel. Older ones, not so much, and this is where intervening with an automatic can prolong the life and health of the engine and transmission.
WILDEBILL308
Well-known member
Yes you would think that but that is not how they work most of the time especially the Allison line. It can be easily shown/documented with a quality EGT gage.Gary RV_Wizard said:
Also you can be in the top of the powerband and still be luging the engine. You have to be in the right gear/ one you can accelerate in.
One good thing is if you see you have high temps on your EGT gage you can reduce the temps almost instantly by just lifting on the throttle. then if/when rpm are low enough you can manually down shift I could go all the way from 6th to 4th at 60 and still not be at max rev.
Unlike coolant temps there is not much lag time. The bad news is the EGT temps can go up just as fast as they come down.
Bill
Utclmjmpr
Well-known member
Also,, "Lugging"a gasser would not necessary be lugging a diesel under the same conditions..>>>Dan
Gary RV_Wizard
Site Team
Unlike the days of carburetors or mechanical fuel injection, you don't siply dump fuel into the cylinders when you push the pedal down. The go-pedal is an advisory to the engine computer that you would like to go faster. The ECM may or may not add fuel, depending on the engine's ability to utilize it.
Skookum
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Gary RV_Wizard said:
Computers have come a long way but in MH's like my Seneca with a 5-speed transmission, it's entirely possible to drive within the computer's allowable ranges and drive EGT up way higher than it needs to be, and moreso if towing heavy. That's a lot of conditions for few gears to cover and the engine runs either at too high RPM or too low RPM for my liking sometimes. A trained driver will know how to split the difference, and if keeping the MH for long time, and on such a big investment, I think it's worth understanding the pro's and con's to letting the computer select a gear or moderate fuel. Most of these things are programmed for efficiency, and that's not always optimal.
If anyone has tuned a diesel, this is an even bigger concern..but if you're tuning, you probably are already aware! Some quick reading for the curious, courtesy of Banks
https://official.bankspower.com/tech_article/why-egt-is-important/
nibroc
Well-known member
)thanks for that Banks link Skookum which as a matter of fact was extremely informative
this has been a good thread
"this has been a good thread" Agree. Thx to everyone that took the time to contribute.
I was surprised to learn of the potential issue with long no so steep grades. I am also looking for a source for a turbo input EGT gauge kit.
mark in MN
I was surprised to learn of the potential issue with long no so steep grades. I am also looking for a source for a turbo input EGT gauge kit.
mark in MN
WILDEBILL308
Well-known member
mark, When you have a chance look at the Banks ligature about where to install your probe for the EGT gage. It needs to be before the turbo. I have installed my probe just before the flange (about a inch or so to give your self room) where the turbo bolts to the exhaust header. Keep us updated.
Bill
Bill
