Shift or Not to Shift

[DegoRed]

Originally Posted by fixit1957

Turbo inlet temps are the first indicator of what the water temperature will be doing. As the turbo spins up and compress the air higher temps are created in the cylinders along with more fuel to handle the load.

If you have watch the turbo inlet temps you will learn how hot the water will get if you continue at that load. If you know from practice that the inlet temps will take the water temps too high slow down a mile an hour or to and watch the turbo inlet temps come into line.

This is exactly what I have experienced as well. On almost all grades I watch Turbo Inlet Temps exclusively, its amazing to see your water temps rise very quickly once your Turbo Inlet Temps get too high.

I do exactly what you said, back off pedal just a bit and temps drop immeadiatly back into acceptable range.

[rvjimzhr]

Can someone please tell me the purpose/function of the MODE position? I was once told it related to fuel economy and I use mine always. I also manually down shift going uphill as necessary, not relying on the Allison to do it for me.

[poppopc]

I shift down to whatever gear will allow the engine to stay btwn.
1800-2000 RPM RANGE . Usually same gear on the way down with
the exhaust brake. SEE SIG. 380- 8.3 cummins.

[Gary RVRoamer]

Surprised to hear that any Allison-Cummins combo ever "lugs" - mine certainly does not. It always pegs the RPMs to the peak horsepower RPM when under load. ABout the only way to make it lug down is to have a dirty fuel or air filter, so that the engine cannot reach full power.

Further, my cooling system (a variable speed hydraulic fan) adjusts its RPMs under ECM control as needed to keep the temperature in an acceptable range. If it cannot, the engine begins to derate output to bring the load down within manageable parameters.

Belt driven fans are probably a different story, since their RPMs is directly tied to engine rpms.

[Sky_Boss]

Originally Posted by Gary RVRoamer

...
Further, my cooling system (a variable speed hydraulic fan) adjusts its RPMs under ECM control as needed to keep the temperature in an acceptable range. If it cannot, the engine begins to derate output to bring the load down within manageable parameters.

Belt driven fans are probably a different story, since their RPMs is directly tied to engine rpms.

At the Spartan Owner's class it was explained that yes, the ECM does have some control but the fan will still turn faster at higher RPM because of the output of the hydraulic pump running it at the point the ECM "locks" it up.

Also...just as a side note. At least on my chassis series/years, if you turn on the dash air to MAX it also appears to lock up the radiator fan. With the AC on my water temps runs around 175-177* and with it off 200-202*. Both of those situations are fairly steady. If I run non-MAX then I see water temps cycle between that 175*and 200*. I'm left to ASSUME that the MAX AC locks the radiator up also. This year I have NOT used the dash AC except in a couple situation with sun into the windshield and have noticed an increased MPG from 6.2 last year to date to 6.7 MPG this year to date and I have done a lot of house AC use along with several nights of generator use for house AC. I suppose that is related to both lower HP draw from the fan and higher water temps with the ISL likes.

As that applies to the topic at hand I now prefer that 200-202* temp range in the climb. letting the temp drop a tad at the beginning of the climb as I manually shift down prior to the climb seems to translate well for temps during the climb.

YMMV.

[TLGPE]

Hi Don,

Until this summer, I never worried about those things. I had read about people shifting around to control the temps, but I never had a problem. Now we are in the Rockies, and it matters. Cruising along at 1500 to 1800 rpm, everything calm and quiet, when suddenly the heat is too high and the alarm goes off; I just didn't realize that we were climbing. Giving it more power can't help, so it just lugs.

I quickly remembered to down shift two or three clicks, and the rpm goes to the max at about 2300, and things get better. Since then I have watched more closely. My KSDP has a belt driven fan, so keeping the water pump and fan running faster helps keep the heat down. The automatic shifter definitely does NOT do the job well. In general for me, it shifts up too soon, and will not shift down soon enough. This is not in the ECOM mode. It's probably worse there.

I hope someday to grow up and get a Dutch Star with the side radiator and hydraulic fan. Never know................

Tom

[BigAWB]

Thanks to everyone who answered. I wanted to know and under stand all I could so as not to be a danger to me and my family or to others.

[fixit1957]

Originally Posted by rvjimzhr

Can someone please tell me the purpose/function of the MODE position? I was once told it related to fuel economy and I use mine always. I also manually down shift going uphill as necessary, not relying on the Allison to do it for me.

The mode option selects normal/economic vs performance mode that is the default. Why is it the default? As it was explained to it goes back to the very first Prevost bus conversions. The default was the economy mode but those owners wanted more RPM and noise thinking back to their car days and RPM IS MORE POWER. This is why they made the default the performance mode.

The routine is start the engine and then hit the mode button for the rest of the trip.

The mode button will kept the engine at lower rpm and closer to peek torque. Peek torque is where the work is done. High rpm in a diesel engine is just running more fuel and more wear on the engine.

All new truck engines run peek torque very low. Several at 1150 rpm.

[Jimalberta]

Fixit this is very interesting. I have a 2001 American Eagle US 40 ft with the 8.9 Cummins and 6 speed Allison. I have been wondering about the mode switch and the economy light but my manual will only mention that the mode switch is for diagnostics.
I just spent a month in British Columbia and guys if you want mountains and grades....this is the training ground . I almost kissed the hiway when I got back to flat ground. Imagine a province the size of Texas that is nothing but mountains.

I have to say too that the coach handled the mountains well it was just me freaking out in a new to me machine learning how it operates in both extreme heat and extreme grades at the same time. I did find that if I kept the fuel pegged to the floor on a long climb such as the Coquahalla.....( tv show Hiway from hell? ) that my check engine light would come on. It was hot out but my engine temp wasn't climbing. however I since learned that if you floor the throttle you are over fueling the engine and thus driving the engine temps up...especially the exhaust temps...that can put you into limp mode and you lose power.

[Ray,IN]

Originally Posted by fixit1957

Two weeks ago we sat in on the Silverleaf seminar at the Fmca Rally in Redmond Oregon. Here is what I learned.

Max engine temp on a Cummins ISL is 226 for 5 min.

Turbo inlet temps are the first indicator of what the water temperature will be doing. As the turbo spins up and compress the air higher temps are created in the cylinders along with more fuel to handle the load.

Almost always use economy mode on the transmission.

If you have watch the turbo inlet temps you will learn how hot the water will get if you continue at that load. If you know from practice that the inlet temps will take the water temps too high slow down a mile an hour or to and watch the turbo inlet temps come into line.

Down shifting on a hard pull and an already high water temp can cause water temps to rise slightly. Remember that on a down shift you be raising the turbo spin rate because of the increase in rpm. This will increase the turbo inlet temps more. It would be best to learn what speed will allow you to keep the engine happy temp wise. Hot days may mean that you crime at 3 mph slower on a 6 % grade that day. Randy

What is used to measure Turbo INLET temperature? The Turbo inlet accepts air from the air filter, the Turbo then compresses it and charges the cylinders. The normal pyromometer is installed in the outlet/exhaust side.

[Peralko]

The mode function programs the transmission to upshift sooner on acceleration, and downshift later going up hills. When I hit a hill that causes the coach to slow down, it will downshift from 6th gear at 55 MPH in normal mode, and with the mode switch on, it will wait until about 45 MPH. I normally cruise with the mode on, and if I encounter a steep hill, I take the economy mode off. Then I let the computer do it's job, unless the engine starts getting hot, and I just reduce speed. I do not worry about manually downshifting.

[Skip426]

For the purpose of this document , secondary mode is " Economy " instructions came from the factory with the coach.
Following them works fine for me.

[Durabil]

All in all the computer does a wonderful "general" job of monitoring speed, torque range and gears ... however, consider anticipating a haul before the computer can detect the extra load. If you see or are aware of haul up a grade, best to select the best gear that will hold the rpms and torque as per manual for optimal range. When you summit and/or start to notice the revs climbing as a grade eases you may want to return the work to the computer and let it manage.

[Mr_D]

When we got our present DSDP I rarely used the economy mode, after adding the Banks kit I use it most of the time. The stock ISC has 1050 ft lbs torque at 1400 rpm, with the Banks I only get down to 1050 at 2100 rpm and above and 1200 ft lbs goes from 1400 to past 1700 rpm.
I did finally encounter some overheating this last trip out. Cummins suggested cleaning the radiator so I did. I was amazed at the amount of junk that came from between the radiator and CAC. Temps are back down, in fact at 60 mph my VMSpc is showing 179° to 183°. Of course ambient temps play into this too.