Regulating water temp on mountain uphills

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Regulating water temp on mountain uphills

June 15, 2021, 09:19:01 pm

Heading west on Interstate 80 today from the Bonneville salt flats where the temperature was 103, up into the Nevada mountains, my water temp gauge hit 210 and the water temp warning lit up on the dash. This happened twice. I was close to the top of the hill each time, where I could pull off and let it settle down to 180 by running high idle in neutral. At the campsite tonight I'm reading the Allison transmission operator's manual and the "Driving Tip" for mountainous driving says "Manually preselect a lower gear in order to maintain engine speed within a range of 500 RPM of engine governed speed. Road speed may decrease but power (torque) will remain at peak output while ascending a grade." What does this mean, and what is the governed speed of my C8.3 325hp engine? Any other tips/suggestions for ascending these hills?

Re: Regulating water temp on mountain uphills

Reply #1 – June 15, 2021, 09:25:30 pm

I believe it is 2500 RPM

Re: Regulating water temp on mountain uphills

Reply #2 – June 15, 2021, 09:40:26 pm

Quote from: oldguy – June 15, 2021, 09:25:30 pm

I believe it is 2500 RPM

Why do I see it at 3,000 sometimes before it upshifts?

Re: Regulating water temp on mountain uphills

Reply #3 – June 15, 2021, 09:43:43 pm

Increasing RPMs increases cooling for the engine and the transmission. If you are running AC from the engine try turning it off, start the generator and run rooftop AC. When you stop and things cool off a bit check the radiator through the side louvers. Rinse off any debris.

Re: Regulating water temp on mountain uphills

Reply #4 – June 15, 2021, 09:49:44 pm

Don't know your governing speed , so what rpm does it normally shift to next higher gear? Preselect on shift pad when climbing to increase engine rpm to below that shift speed and relax a little during the climb with higher rpm and slower speed. Everthing will be happier in the long run. Okay to down shift several times and watch the 320s roar by

If your temps are climbing slower speed, higher rpm , lower power setting will reduce temperatures.

Re: Regulating water temp on mountain uphills

Reply #5 – June 15, 2021, 09:50:11 pm

Like the book says. Slow down and select a lower gear.

You are not in a race. Most people think they know about diesel engines. And mistakenly think that you are supposed to lug a diesel. They do not like to be lugged down too low while at full throttle and max turbo boost. So if you are at 1000-1500 RPM and at full throttle to just maintain your speed, this raises the exhaust gas temps to dangerous levels. The exhaust temps are what is throwing heat into the engine/water.

You need to slow down and keep down shifting until you do not need to have the throttle to the floor to maintain your speed.

Just to clarify lugging. Most engines operate most efficiently in the upper third of the RPM range.

If I start pulling a 3-4% hill in our rubber band powered Subaru in 6th gear (2500 RPM) It won't make it. I have to be revving the crap out of it in a lower gear as max HP is AT redline. A very dreadful engine.

Re: Regulating water temp on mountain uphills

Reply #6 – June 15, 2021, 10:30:25 pm

I googled the 8.3 and it is 2500 RPM and the M11 is 2100. When I had an
8.3 engine on a long pull I would run at least 2000 and higher.

Re: Regulating water temp on mountain uphills

Reply #7 – June 16, 2021, 01:21:56 am

Like bigdog said, slow down and use a lower gear. Get in the right hand lane and keep you eye on the temp gauges. Maybe turn on your emergency flashers. I usually pour a cup of coffee and check out all the burned pavement as I'm going up those grades.

Re: Regulating water temp on mountain uphills

Reply #8 – June 16, 2021, 07:53:08 am

Call Cummins with your engine serial number to verify the following for your engine-- info every owner should know:

Peak torque RPM
Peak HP RPM
Governed RPM
Max no load RPM

Cummins 800-286-6467

As far as driving, good advice so far, 2000 RPM or so (just below peak HP), in a gear that leaves you will a little throttle. Said another way, you are just short of WOT. Use the Allison shift pad down arrow to lock you in that gear so it doesn't try to upshift until you determine the grade has lessened enough to allow the upshift.

If no place to pull over, in an emergency, turn on the dash heater and fan to high. It IS another "radiator". Better to be warm for a few minutes than to loose an engine.

If you can pull over, do not shut off the engine unless the overheating is due to coolant loss. Leave it in neutral and at around 1,500 RPM. Temperature will quickly return to normal.

If you know it will be a long grade at high ambient temperatures and you have a passenger, consider having the toad driven separately.

Preventive measures:
Clean CAC and radiator. Simple Green EXTREME is an excellent, aluminum-safe degreaser.
Make sure coolant is good (both chemically and system full).

Re: Regulating water temp on mountain uphills

Reply #9 – June 16, 2021, 07:53:32 am

Quote from: Dan & Annie – June 15, 2021, 09:19:01 pm

1. ...what is the governed speed of my C8.3 325hp engine?

2. Why do I see it at 3000 sometimes before it upshifts?

1. At Cummins QuickServe Online there is a listing of the important RPM numbers for my C8.3 300hp engine. They are reproduced below. The numbers for your engine should be similar.

ADVERTISED HP: 300 @ 2200 RPM

GOVERNED HP: 285 @ 2400 RPM

TORQUE PEAK (lb-ft): 820 @ 1300 RPM

HIGH IDLE: 2760 RPM

GOVERNOR BREAK RPM: 2450

2. If you are seeing 3000 rpm before your engine upshifts, I suspect your tachometer is inaccurate. I seriously doubt your engine is really revving that high. "HIGH IDLE" is what Brett refers to as "max no load RPM". This is the RPM that engine would reach if you put the transmission in neutral and floored the accelerator pedal untill the RPM stabilized. You should NEVER exceed this RPM under ANY normal circumstances.

Sign up for FREE at QuickServe Online for a wealth of info on your specific engine. All you need is your ESN (engine serial number) which is found on engine data plate. Lots of White Smoke

Cummins QuickServe Online

Re: Regulating water temp on mountain uphills

Reply #10 – June 16, 2021, 11:50:04 am

Since the question has been answered I will re tell a short story. While at a camp ground a neighbor was telling me about his Cummins in his coach being "dusted" , his term.. While going up a steep grade out west in the summer heat his motor kept getting hotter and people still kept passing him so he kept pouring the coal to it. Bottom line he burned it up and had to buy a complete engine. He was one who didn't listen well so I didn't get far into telling him how to climb a hill before I shut up.. people are going to pass going up grades and one has to drive THEIR drive. Like said above stay focused on coolant temp and rpm.. already said but 2000 to 2100 rpm giving the engine 3/4 to half it's throttle will keep temps the coolest it can be and give no consideration to speed or what is passing you. This is the reason I don't agree with "turning up" fuel to an engine. If you use the power you gained in a climbing situation you are more likely to burn an engine. If you can't use the power why on earth have it pray tell.

Re: Regulating water temp on mountain uphills

Reply #11 – June 16, 2021, 11:53:17 am

Dub,

You new CG "friend" probably picked up the term "dusted" on the internet-- where everything you read is true.

But, for the rest of us, dusted means that the engine ingested enough dirt to wear it out-- Generally from an old/damaged/wet air filter.

Re: Regulating water temp on mountain uphills

Reply #12 – June 16, 2021, 12:46:19 pm

Quote from: Dan & Annie – June 15, 2021, 09:19:01 pm

"Manually preselect a lower gear in order to maintain engine speed within a range of 500 RPM of engine governed speed. Road speed may decrease but power (torque) will remain at peak output while ascending a grade." What does this mean,(?)

It means that you're going to be passed by higher horsepower lighter vehicles.

As others have pointed out, holding the foot feed to the floor is not a good thing.

Downshift until you're not holding the foot feed to the floor, and if you choose to so do you can accelerate, but don't.

FWiW, on Memorial day Duke, the Dog snatched me off my feet and I broke my fall with my right eye on a lead acid battery case.

On Thursday the 10th of June I had to drive the 903cc Siata the 90 miles to Savannah, GA and back in the heat of the day. 3,400 rpm gave me 45mph and kept the temperature gauge just out of the red. And gave me 45 MPG.

We operate the machinery within its capability and not our desire.

Re: Regulating water temp on mountain uphills

Reply #13 – June 16, 2021, 12:54:18 pm

I'm not sure the man yet understands how his "dusting" occurred. He seemed more concerned with the vehicles passing than anything else. Without changing his habits he hasn't burned his last. This thread is a read that all NEW Diesel pusher owners needs to study.. As of late we have a number of new people that may or may not have operated a 30,000 lb plus rig in the summer heat.. Many have just driven the family van which will take care of itself in a hot climb IF the coolant system has no weak points..Buying an engine can put a strain on most budgets not to mention the 2 or 3 week down time in a small town where all parts have to be shipped in at a premium.

Re: Regulating water temp on mountain uphills

Reply #14 – June 16, 2021, 01:10:58 pm

Here is my note on my 1997 8.3.
jor

Engine
Cummins C8.3 (504 cu)
Engine Serial Number (ESN): 45473701
Date of Manufacture: February 3, 1997
Idle Speed: 750
Governed Speed: 2400
Blow Up Speed: ?
Advertised Horsepower: 325 @ 2200
Peak Torque: 915 @ 1300
Compression Ratio: 17.3:1
Weight (dry): 1330#
Reference Number:
Maximum Coolant Temp: 212
CPL2169

Re: Regulating water temp on mountain uphills

Reply #15 – June 16, 2021, 02:04:32 pm

Not to vary to far from the subject. But there was a great example of to high an engine duty cycle. It was in Formula 1 when they went from the V-10 to a V-8 engine. It was very literally the same engine, As all they did was chop off the two rear cylinders and put in new valve gear and cylinder heads.

Suddenly the engines started blowing up with alarming regularity. The F-1 engineers were perplexed. UNTIL they looked at the throttle positions on identical cars and tracks. With the V-8 and the old V-10 being the only difference. The lower HP V-8 had the drivers holding the throttle to the floor a much higher percentage of the lap. The V-8 was operating at nearly 100% duty cycle. It couldn't cool off and was over stressed and blew up.

It is the same with any engine.

Re: Regulating water temp on mountain uphills

Reply #16 – June 16, 2021, 02:55:47 pm

When they were building the Mica Dam in BC they were blowing engines
transmissions and rear ends in the 100 ton belly dumps. The cause was the
engines were running full racked. They cut out 6th gear and everything had
a chance to cool down and the problem went away.

Re: Regulating water temp on mountain uphills

Reply #17 – June 16, 2021, 02:57:35 pm

Quote from: Dub – June 16, 2021, 11:50:04 am

This is the reason I don't agree with "turning up" fuel to an engine. If you use the power you gained in a climbing situation you are more likely to burn an engine. If you can't use the power why on earth have it pray tell.

Just because you have extra power doesn't mean you always have to use it, but it's nice when you want it. With cooler ambient temps, you can use more power, longer, to pull that grade. It also gives more power for passing. If you are going to monitor the engine temps anyway, why not have more power?

Re: Regulating water temp on mountain uphills

Reply #18 – June 16, 2021, 03:16:54 pm

Quote from: WS6_Keith – June 16, 2021, 02:57:35 pm

Just because you have extra power doesn't mean you always have to use it, but it's nice when you want it. With cooler ambient temps, you can use more power, longer, to pull that grade. It also gives more power for passing. If you are going to monitor the engine temps anyway, why not have more power?

That would ASSUME (yes, a big assumption) that all who want more power also know how to use it properly. Sadly, in many cases an erroneous assumption.

Re: Regulating water temp on mountain uphills

Reply #19 – June 16, 2021, 03:49:23 pm

Overheating is a common result from letting coach drive itself. 'Secret' is for us to drive coach.

Only pressing throttle pedal is always the wrong thing to drive up hills/mountains.

Like you, years ago, we once saw our Cummins C8.3 engine coolant temp gauge climb over 200 degrees and after figuring out how to drive, we now usually see 180-185 and have not seen anything over 190 degrees.

On our dash we made an informational sign:

Peak Torque = 1200-1400

Peak HP=1800-2000

Our style is to manually DOWNSHIFT to keep RPM around 1500-1800. Usually finding 3^rd gear is about 30 mph, 4^th gear about 40 mph, and on occasion 2^nd gear about 20 mph. We never push to engine limitation.

We usually find we are letting up on throttle pedal rather than pressing throttle pedal. Every further press on throttle that does not increase rpm is sending more fuel than needed and causing increased engine heat.

Adding an exhaust temp dash gauge (pyrometer) will add to engine temp knowledge. Also a fuel pressure dash gauge can be helpful.

Replacing our big old (internally) rusty OEM muffler with a resonator, replacing our OEM fuel lift pump with a new one and replacing the injector fuel return valve all seemed to give us a little more power and probably helped engine to run cooler.

Good luck. . .

Re: Regulating water temp on mountain uphills

Reply #20 – June 16, 2021, 03:55:37 pm

Many RVs find out that winter driving and summer driver are way different. High altitude and high temperatures make cooling management important to keep your engine healthy.

Parent bore engines like the 5.9 Cummins, 3208 CAT will tolerate a little higher temperatures, Wet liner engines like the 8.3, 10.8 Cummins, Detroit 6V-92TA, 3176 CAT have sealing rings at the top and bottom of the wet sleeve and need a little more care when it comes to high engine temperatures.

I don't let the temp go past 200 without slowing/gearing down, keeping the rpm up at about 2000. If that does not do it, I drop another gear. As an example, we can charge up and out of Death Valley in the winter without a thought about temperature but in summer, I've had to go down to first gear to keep the temp down.

Pierce

Re: Regulating water temp on mountain uphills

Reply #21 – June 16, 2021, 04:03:26 pm

Quote from: Barry & Cindy – June 16, 2021, 03:49:23 pm

Overheating is a common result from letting coach drive itself. 'The Secret' is for us to drive coach.

Yes, the magic words. You do NOT put in in "D", set cruise control and go-- unless you have a very thick wallet that you want slimmed down.

Re: Regulating water temp on mountain uphills

Reply #22 – June 16, 2021, 05:03:03 pm

On our coach pushing the MODE button on the Allison touch pad makes the transmission much more willing to automatically down shift on grades, and to hold the lower gears longer when moving from slow speeds up through the gears to cruising speed. I use MODE a lot in the hills cuz I like the feel of the Allison smoothly shifting up and down, and it makes the coach seem more lively. A plus is the fact that it tends to keep the engine RPMs higher and coolant temps lower.

Re: Regulating water temp on mountain uphills

Reply #23 – June 16, 2021, 05:11:09 pm

Quote from: wolfe10 – June 16, 2021, 03:16:54 pm

That would ASSUME (yes, a big assumption) that all who want more power also know how to use it properly. Sadly, in many cases an erroneous assumption.

Ding, Ding. You win the prize Brett. Having power and being able to manage said power is sadly a gap not often bridged. It might even be worse with a lower power engine. As most just throw a heavy rock on the throttle of a low power engine.

Re: Regulating water temp on mountain uphills

Reply #24 – June 16, 2021, 05:30:55 pm

Quote from: Chuck & Jeannie – June 16, 2021, 05:03:03 pm

On our coach pushing the MODE button on the Allison touch pad makes the transmission much more willing to automatically down shift on grades, and to hold the lower gears longer when moving from slow speeds up through the gears to cruising speed. I use MODE a lot in the hills cuz I like the feel of the Allison smoothly shifting up and down, and it makes the coach seem more lively. A plus is the fact that it tends to keep the engine RPMs higher and coolant temps lower.

While either Power or Economy mode can be the "primary" mode (i.e. when you turn the key that is the mode is goes into until you press the mode button, 99% of motorhomes come with power mode as the default and you have to push the mode button to get economy mode. Amy Allison dealer can set either power or economy mode to be the default setting.

In power mode, the transmission acts as you suggest-- keeps RPM higher on both up and down shifts under high throttle.

My approach is different-- more "manual transmission" more "driver control": I am in economy mode 99% of the time and use the down and up arrows to change that. The only time I am in power mode is if I say "I am willing to pay a lot more fuel for a little more performance"-- passing on two lane roads for example where I don't want to take my eye off the road to upshift.

There is NO "correct way" to do this. One has to balance what is best for THEM.

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