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Old 07-23-2006, 09:03 AM   #29
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Audrey I use the same tactic as Dave. I do draw the line at 204 degrees and down shift to maintain 2000 RPM and just go slower. I am usually in no big rush anyhow. I have read the Silverleaf guide but chose not push the envelope.
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Old 07-23-2006, 10:04 AM   #30
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Engine temp in a turbo diesel isn't as straight forward as in a naturally aspirated rig. Higher RPMs generally mean higher Intake Air Temp, and therefore higher in-cylinder temp and higher Exhaust Gas Temps than a lower RPM, due to heat of turbo boost (compressing air causes heat). EGT is the penultimate determinant of engine heat load.
BUT, the variable geometry turbo of the Cummins can alter the IAT (and therefore EGT) based on how the ECM (computer) modulates the turbo boost. Higher boost = higher IAT/EGT, though somehwat ameliorated by the intercooler. And the modulation will be based on input from the Accelerator Pedal Position sensor (APP, throttle or gas pedal) which is used by the ECM to choose fuel rates and boost targets (more Foot-In-Gas = more fuel & boost and vice versa). In essence the amount of FIG is the most direct operator control of engine heat load.
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Old 07-23-2006, 12:42 PM   #31
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Wayne- As usual, I overshot. The point I was attempting to make was that upping the RPMs won't necessarily optimize engine heat. IMO, its the FIG. If ECM is demanding much boost for the higher revs, that may be more heat than one gear higher @ lower revs w/same FIG. Based on my driving so far, I'd say that sometimes the lower gear will be less heat, and sometimes the higher gear will be, but it isn't something I have a precise formula for controlling.
If we didn't have the intercooler, I can state flatly it would be better all the time for the higher gear/lower revs for engine heat. I did a lot of driving w/an EGT gauge on my last diesel (w/out intercooler), and wound up driving by the EGT gauge because of this issue. It meant 2-300 degrees lower EGT to run in the higher gear, which when that means the difference between 1000 and 1250 on a sustained grade, that's a critical difference that comes from lower boost temp.
For the Cummins w/intercooler, as I perceive it so far (note I don't have the EGT gauge which is instantaneous vs coolant temp which may lag EGT by 2-3 minutes), gear selection is sort of blind due to the number of variables, whereas FIG is more absolute- less fuel = less heat.
Said another way, because of the heat of turbo compression (which is higher @ higher RPM), the cooling effect of running more air thru the engine that a non-turbo engine sees w/higher revs, isn't so clearly available. Whether you'd get a cooling benefit depends on the intercooler's ability to waste the compressor heat fully. I doubt it can with the tranny & motor radiators, in the same stack as the intercooler, running @ 210. Ordinary non-turbo IAT is equal to the ambient temp, but ours is probably near double that on a small grade, maybe more @ higher revs. some of the time, almost certainly more on a steeper grade @ higher revs, and that added 100 degrees+ has nowhere to go but into the coolant.
After I finish my more useful home remodeling projects (2 more basement sliders, compressed air storage, inside voltmeters... and a few more OEM fixits like getting the radiator fan working when idling in traffic), I'll probably add an EGT gauge to see this issue real time.
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Old 07-23-2006, 01:09 PM   #32
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Mike, on my 2000.5 Alpine with an intercooled 350 and the Banks Power Pack which included the EGT. I found the same driving techniques that Dave and I described to be the most effective. I even installed a " Desert Cooler and played with it a bit. Never got in the right conditions to prove it out though. 100 degrees and no humidity like we are seeing in Eastern Washington now.
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Old 07-23-2006, 04:15 PM   #33
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We just drove from Page, AZ. to Lemon Grove,CA. via Phoenix and Yuma. Outside was 110 to 117. I always kept the rpm's around 2000 on the hills and hardly ever went over the 200 peg. Granted sometime we were down in third.
Also tried to run the gen/set w/ front air. Worked great until outside got to 115. Mostly kept drivers/passenger area about 80. Around Gila Bend the gen/set quit and the 3 light flash said "High Temp." I have a remote temp sender in the front gen/set compartment and it read 125. Sounds hot to me. After that it was 115 outside and 100 inside.
Now we are in Lemon Grove. 90 and fine although both airs are running. Forgot what humidity was like.
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Old 07-23-2006, 04:21 PM   #34
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Mike, are you saying higher RPM's equals higher boost? Pulling a hill at 50 in 5th is probably around 1500 rpm like Audrey says. But the FIG is on the floor, boost is probably around 21-22 lbs. Shifting to 4th RPM's will come up to 2100 but the foot comes off the floor and boopst will drop to around 18-19. Boost drops, FIG comes off the floor...less fuel, less boost equals less heat.

Don't you think boost is more related to FIG than RPM?

We just pulled a 5 mile 6-7% grade at 44 mph in 4th. Around 1900 RPM I think. H2O temp rose to 201, tranny around 199. Outside temp 105, at the bottom of the grade.
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Old 07-24-2006, 09:24 PM   #35
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Tom- First, I like your 201 a lot better than 210+ as was mentioned earlier. IIWM, I'd be looking for why my temp was over 205. A partially clogged radiator could be the issue. I've never seen over 205, even on a long 7% pull in August, except when the radiator fan isn't working, but I'll get that fixed.
Second, yes I'd say that lower fuel and boost will be lower EGT & coolant temp.
But what you've described demonstrates how fuel/boost tables have become fairly complicated. Used to be FIG = fuel rate, and RPM = boost. Now FIG still equals fuel rate, but boost is modulated based on IAT, MAP and or MAF, APP demand, and possibly torque feedback, and GKW else. The tables are the solution of complex chemical equations that try to optimize air + (the complicated chemical compound) diesel to provide power while minimizing adverse air emmissions. If'n it were not for that pesky smog, this would be simple.

One thing for sure about all diesels- when you get to the point where you step further on gas, and you don't feel a propotional difference in go-go, you are adding heat disproportionately, and pouring fuel thru the tailpipe along with it. This is related to the statement earlier that "a diesel will work until it dies. But a properly designed & properly working coolant system will manage practically anything we throw at these rigs w/style (one of the beauties of a DP). And IMO, the Alpine coolant system is nicely oversized. That's why I mentioned that 210+ looks improperly high to me; either some coolant is wearing out, or the rad cap is weak, or the radiator needs cleaning, or maybe the rad fan isn't up to speed.
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Old 07-25-2006, 09:43 AM   #36
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Why does 210+ seem like a problem? The Silverleaf document says it's OK to climb hotter than that (but not much hotter). The engine only has 10,000 miles and was recently serviced (annual service). The VMS system goes into yellow zone at 209 degrees.

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Old 07-25-2006, 10:39 AM   #37
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I do not think 210? is too high I was told that over heating is 225?. I was told and I am following the advise I was given and I use 210? as my cut off point to start attempting to back off the power and not permit any higher coolant temps. I do not want to get to 225?! So by maintaining over 2000 rpm including backing off on the throttle and down shifting, maintains my coolant at a lower temps so I hopefully never reach my cut off point.
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Old 07-25-2006, 07:46 PM   #38
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Isn't all this talk about coolant temp, EGT, TIG, and all the other acronyms much ado about nothing? Diesel trucks have been pulling heavy loads up long steep grades for at least 70 years-- I myself for 50+. How did we do it before turbo-boost, RPM guages, Silverleaf and all the other new-fangled engine monitoring devices?

We started up the grade and kept down-shifting until 2/3 throttle would maintain speed [perhaps 10mph in the early days]. "Floor-boarding" the fuel pedal would needlessly waste fuel and was hard on the engine. If your exhaust pipe tip was glowing red as you climbed-- you were just right.

The only reason to glance at the coolant temp guage was to be sure it didn't climb into the red zone thus indicating a blown coolant hose or a worse problem. We never worried about whether the coolant was at 199, 201, or 208.

I have yet to drive my own Alpine but I will bet that all the old principles still apply.

Postscript: As I read the above posts I kept wondering why there was such concern about coolant temp-- then it hit me. It's because of the digital readout on the Silverleaf monitor. So people keep watching their temp. Folks, it simply does not matter unless the temp pops into the red warning status. It is a case of information overload made possible by digital output. Try monitoring something else and enjoy the trip.

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Old 07-26-2006, 07:22 PM   #39
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Dave Fernandez:
I do not think 210? is too high I was told that over heating is 225?. I was told and I am following the advise I was given and I use 210? as my cut off point to start attempting to back off the power and not permit any higher coolant temps. I do not want to get to 225?! So by maintaining over 2000 rpm including backing off on the throttle and down shifting, maintains my coolant at a lower temps so I hopefully never reach my cut off point. </div></BLOCKQUOTE>
That makes sense to me Dave. The Silverleaf Seminar suggests using 205 as time to take action to manage the heat, and so that's generally what I've been doing.

OK Folks - Tomorrow is the big "Cabbage Hill" day. (Knock on wood).

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Old 07-26-2006, 08:09 PM   #40
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Audrey and John,

I've been wondering where you were. I keep looking over at the WRV lot for a coach your color. We have the same color but in 34'. I have property across the street from the service center, so I'm there most days. Thought I'd stop over and say Hi.

Regarding Cabbage Hill, with your Jake on Hi you'll find you have to use the gas pedal to go fast enough downhill. Pretty much like every other hill. I have to travel Cabbage Hill all the time. The biggest risk to me is the Indian Casino at the bottom of the hill.

Have a good Trip in to Yakima.

TerryM
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Old 07-27-2006, 05:21 AM   #41
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Hi Terry. We'll get there Sunday afternoon and hookup. Our appointment is Monday.

We'll probably stay in Toppenish this weekend.

Audrey
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Old 07-27-2006, 05:36 PM   #42
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I believe this has been a very long issue about going up & down large hills. I realize before you jump all over me that I have done a number of pretty good sized mountains and let the engine, the transmission & the Jake brake do its job. They have been absolutely wonderful. I think you just want to go over the d*** hill and be done with it. Forget all the strange talk and just do it. The hill is not going to change. If I had any concern at all it would be brakes, period.
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