Running in the mountains in the morning

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Running in the mountains in the morning

June 06, 2019, 12:23:35 am

Well, I have made it from Florida to Colorado Springs so far with my 2000 U270 with the 8.3 and Allison combo, but I leave in the morning and will be running through Denver on the way to Yellowstone and eventually end in Fairbanks AK where I will be living. My question is what RPM is too much when climbing the steep grades on the big mountains between me and Alaska. I am pulling about 6500 pounds and my RV weight is right at 28k as it sits

Re: Running in the mountains in the morning

Reply #1 – June 06, 2019, 12:25:23 am

Also what temps are y'all running during the steep inclines on gauge

Re: Running in the mountains in the morning

Reply #2 – June 06, 2019, 01:16:48 am

I have an ISM11 so it might be a bit different than your engine. 1700 on a long haul up, maybe a bit more. Coolant temps get to about 190. Transmission 195. Maybe 45 mph in 4th. About the same going down 4th or 5th, one notch of retarder, maybe 2. Whatever speed feels safe. 45ish. Use the service brakes firmly to slow down not to maintain speed, lower gear and retarder first.
Use the service brakes on the straights before the curves to slow down enough to drive through the curves w/o brakes. That means slow down. The yellow speed signs are absolute max speeds for you. Higher RPMs get more cooling and reduce engine load. The correct speed is what you are comfortable and safe doing.

S to N through Yellowstone, Big grades through Mammoth. Probably better through W Yellowstone and then N Coming that way from Tetons and you will cross the Continental divide three times. Good roads, 45 mph speed limits.

Re: Running in the mountains in the morning

Reply #3 – June 06, 2019, 01:39:41 am

I think we have the same setup (ISC350). If you don't have Silverleaf, it would be a good investment. It will give you a digital display of the retarder temp as well as the gear you are actually in. Both essential when driving in the mountains. Of course, it provides a lot of other info, but those two parameters I find the most useful. Contact Roger (of Roger and Susan) for information on Silverleaf. I would not drive in the mountains without it.

The rule of 50s in 5th, 40s in 4th and 30s in 3rd works pretty well. You are probably going to have to do some downshifting manually and it is critical to get the speed right before downshifting. Remember the controlled max for that engine 2200 rpm.

When driving in the mountains you have to keep an eye on your retarder and engine temps. Going uphill with that load you don't want the engine temp to get much above 185 degrees. When it starts to creep up I slow down and downshift to a lower gear and higher RPM. That usually solves the problem.

Likewise, when going downhill you need to control your retarder temp. If you don't have Silverleaf I guess you can use the transmission temp as a guide but in my experience, it lags way behind the retarder (i.e., the retarder will be a lot hotter than the transmission temp). The rule about going down a hill in the same gear you came up the hill in is generally a good one. But with all that weight you have, it might be a good idea to start at the top one gear lower and slower. Again the MPH vs gear guide should be followed. Avoid going too fast at all costs. Use your brake to slow down, but don't ride the brake. You should be able to control your downhill speed with the retarder and transmission gear. When you get the combination of gear and retarder setting right it will go down the hill in a controlled manner without overheating the retarder. You might have to occasionally apply the brakes to bring down the speed. But if you are applying them too often, slow down and drop down a gear to control your speed.

Driving in the mountains is a very active process. For me, it takes a lot of concentration. It is NOT like driving a car.

Re: Running in the mountains in the morning

Reply #4 – June 06, 2019, 10:34:02 am

If you are going to be driving in any sort of mountainous area on a regular basis, Silverleaf is a VERY useful tool and will take your driving skills to a whole 'nuther level. Jeff could concentrate on the driving, and I would call out the numbers to him as they rose and fell ... making sure he was always in the best parameters for our engine. I also checked the route with our Mountain Directory, to be prepared for any steep grades up or down. Knowledge is power!

Re: Running in the mountains in the morning

Reply #5 – June 06, 2019, 10:48:39 am

You have a pretty good load. I'm 31k pulling a 4600lb Jeep. When pulling a steep grade I try to keep about 1800 RPM, and keep temps below 205. In warmer weather you will have trouble keeping temps at 185 pulling hard. Just don't worry about folks passing you, drop down manually to what ever gear you need to keep things cool and calm. Same goes with down hill.

Re: Running in the mountains in the morning

Reply #6 – June 06, 2019, 10:50:37 am

I find that 1 click on the retarder will raise the retarder temp 10 or so degrees. 2 clicks about 20º. 3 clicks or more the temps will start rising to 250º pretty quick. So like Roger said 1 or 2 clicks will work best to slow down ahead of time or to maintain speed with some occasional brakes applied. But a VMSpc is your friend!
When do you think you'll get to Fairbanks? We're in Carcross, YT near Whitehorse now and heading into AK in a few days.

Re: Running in the mountains in the morning

Reply #7 – June 06, 2019, 11:38:56 am

Our engine has a fuel cutoff at 2130 RPM. Climbing grades, I don't think much about bring it up to that number during normal acceleration or climbing grades. I try to keep RPMs up to at least 2000 on grades as it circulates coolant best at that speed and also keeps EGTs down. If the temperature gets to 200-205 degrees, I back off the throttle, shift down and then keep engine RPMs up to around 2000. One thing to avoid is loading the engine at lower RPM as it WILL cause higher EGTs. High altitude and warm temps translate to high density altitude so a 7000 foot map elevation can easily translate to 9000 feet or higher. EGTs can soar especially in mechanical engines. The cooling fan is much less efficient up high and since the air is so much less dense, the radiator is much less efficient in transferring heat to the air passing through it. Translation: going up a 6 percent grade at high altitude will see much higher coolant temps that you may be used to a low elevations.

So, climbing grades, don't let your transmission "hunt" from one gear to another. Just slow a bit and use the lower gear at high RPM to climb the grade watching the engine temp as you go up.

Don't shut the engine down after getting to the top for photos, lunch, etc without a 1000 RPM fast idle for at least five minutes. Oil temperature cools slower than coolant temperature and petro oil will coke in the turbo shortening its life.

Watch your air pressure before you start down a grade and several times during the descent. Choose a lower gear and high RPM during the decent to make use of the maximum engine braking so you don't have to use the retarder constantly and overheat it. Don't use the service brakes continuously but rather intermittently. Best to descend in a lower gear. Stop and let them cool if in doubt and before it's TOO late.

We spend a lot of time in Yellowstone so PM for tips, campsites, etc.

Pierce

Re: Running in the mountains in the morning

Reply #8 – June 06, 2019, 12:37:36 pm

We have 2000 U270 with ISC 350. From the Cummins data sheet I posted this on our dash. Never failed us last year out west on steepest grades.

Re: Running in the mountains in the morning

Reply #9 – June 06, 2019, 01:34:28 pm

My opinion is that almost all motorhomers baby their engines excessively. If the temp gauges move they are concerned.

Not that they should not be but these are made to be driven hard in a stick shift truck carrying heavy loads.

The dash gauge on my coach is too high by at least 10 degrees versus VPMS's readout.

We took over our 97 at 100k miles. As usual it had never been driven hard.

I have a heavy foot. Engine pulled grades better after stretching its legs for the next 15k Miles.

Commercial m11 engines in a big rig do not turn on their electrical cooling fan until 210.

Thermostat does not even fully open until 195.

If I were in your 8.3 it would show 220 on the temp gauge before I did anything to compensate

Do not be afraid of it. Drive it.

Re: Running in the mountains in the morning

Reply #10 – June 06, 2019, 02:45:11 pm

You have wet liners just like our Detroit. Being smart and conservative is not being afraid of it. No one else is going to pay for a $30,000 overhaul down the road. Overheating damage is cumulative so it may not catch up until thousands of miles later. Who is in a hurry to get up the hill anyway?

Driving up to fuel cutoff RPM, using full throttle from a stop sign, on freeway on ramps, grades, etc is just normal driving for a truck diesel and not running it hard. I've pulled trailers with aircraft on them coast to coast twice using full throttle almost all the time in our 300SD. It has well over 400,000 miles and still as good as new. Not taking care of your EGTs on grades, overheating, shutting down before oil temperature has stabilized, is not just running it hard but abusing your only source of motive power. Who wants to be stuck in a small town waiting for an overhaul for weeks?

Pierce

Re: Running in the mountains in the morning

Reply #11 – June 06, 2019, 03:05:35 pm

On my 1999 U270 cummins told me to keep it about 2000 RPMs and downshift manually to keep the RPMs up as well.

Re: Running in the mountains in the morning

Reply #12 – June 06, 2019, 06:54:35 pm

As Pierce said , run it it will not hurt it to work hard. Just keep the RPMS up around 17-1900 and the temps below 210 life will be good. Shift it manually on the hills if you need to. The 320 folks with the M11s are a whole different animal, they make power at lower RPMs. ISCs have to turn a bit higher to be happy. I average 8.5 mpg, locked in 5th up to 62 mph good power and drive ability, over 62 mph 6th gear. The worst thing you can do is turn these smaller diesels to slow, back in the old days it was called lugging the engine.

Re: Running in the mountains in the morning

Reply #13 – June 06, 2019, 07:13:07 pm

Out of curiosity, what rpm should those of us with the m11 be looking at? Cruising this weekend at 70, the engine was running 1500 rpm.

Larry

Re: Running in the mountains in the morning

Reply #14 – June 06, 2019, 08:25:04 pm

M11 should max at 1800 RPM so climbing long grades would seem that 1700 would be a good engine speed for circulating coolant and keeping EGTs down. Just because it will climb the grade at a lower RPM doesn't mean it is the best for the engine. It is only a 10.8 liter engine so while it is about the same displacement as a 3208 CAT, it produces more power. Lots of big rigs have 15-16 liter engines.

Tough to really "lug" a diesel with an Allison as it makes most (but not all) of the decisions for us. Using RPMs up to the rated maximum won't hurt the engine. High EGTs can, plus don't think for a second that a 210 degree temperature gauge reading is uniform throughout the engine. Low RPM (slower coolant circulation) may allow hot spots around the exhaust valve to actually vaporize the coolant next to the valve area so no coolant actually is in contact with the hot metal. This can cause cracks, loosen valve seats, cause the valve not to seat completely so it can't transfer it's heat to the cylinder head. Most Cummins failures seem to be on number 6 cylinder. Doing a search online, number 6 also comes up a lot. I met a Cummins mechanic from a repair facility in Albuquerque. He also said number 6 was the cylinder that failed more often that the others. I think keeping the valves adjusted, keeping the EGTs within limits with a good RPM for both EGTs and coolant circulation will insure the M11 (or any engine) will live a very long life.

And remember that high altitude, high ambient temperatures will mean less cooling efficiency and higher EGTs. The high EGTs can also crack exhaust manifolds and damage turbo vanes.

Read this and then drop a gear and let the engine breathe: Why EGT is Important | Banks Power

Pierce

Re: Running in the mountains in the morning

Reply #15 – June 06, 2019, 09:01:26 pm

My only comment is when descending a hill, grade, or mountain, when braking is required do not ride the brakes, apply them hard slow your vehicle to a safe speed then completely remove your foot or totally release the brakes. If you ride the brakes they will heat and fade. By using a hard application and then removing pressure you allow the rotors to cool in between applications. Your retarder or Jake brake is your best control when descending steep grades.

Re: Running in the mountains in the morning

Reply #16 – June 06, 2019, 09:28:35 pm

M11 maxes at 2100 if memory serves me. I do not know of a m11 here with an EGT gauge.

Stock it was nearly impossible to "lug" our m11 with the Allison attached.

The trans says not enough torque here so downshift the engine.

Just what was described.

I fixed the parasitic losses and unrestricted the exhaust and now the motor "lugs" much better.

Versus downshift and rev always under 2/3rds throttle now the coach torques up medium grades.

Driven a lot of other 11-14 liter diesels in SOB's and now our m11 runs like them.

I did not touch the engine ECU or the trans. Just put more power into it.

No heating. Gauges look the same. Mpg went up.

Thought the m11 was gutless. Better now.

Trans holds gear at 1300 rpm or so under a fair amount of throttle. And accelerates in the upper gears without a downshift unless floored. 'This is in power mode.

Did not like the stock setup. Might as well been a giant gas engine the way it ran stock.

I feel that the restrictive exhaust stock should cause more heating.

Re: Running in the mountains in the morning

Reply #17 – June 08, 2019, 10:16:11 am

Foliver we should be there around the 14-15 of June

Re: Running in the mountains in the morning

Reply #18 – June 09, 2019, 08:22:54 am

Thanks for the info Pierce and Bob. I just keep on learning.

Larry

Re: Running in the mountains in the morning

Reply #19 – June 09, 2019, 10:04:47 am

Does anyone "mist" their radiator for better cooling? Thoughts on that?

Wantabe
1986 gas Grand Villa

Re: Running in the mountains in the morning

Reply #20 – June 09, 2019, 10:08:07 am

Wantabe,

I would consider that a technique of last resort.

You would have to use distilled water or the radiator (and CAC on a diesel) would quickly become mineral encrusted. Rust would also be an issue.

I would systematically go through the rest of the "likely suspects" before even considering it.

BTW, you need to let us know if you have a front engine or rear engine gas coach-- cooling systems are totally different.

Re: Running in the mountains in the morning

Reply #21 – June 09, 2019, 10:41:14 am

I drive in the mountains all the time and I don't use brakes when descending unless I am in too high a gear and then brake just
long enough to get into a lower gear so the engine brake will hold.

Re: Running in the mountains in the morning

Reply #22 – June 09, 2019, 10:46:16 am

Quote from: oldguy – June 09, 2019, 10:41:14 am

I drive in the mountains all the time and I don't use brakes when descending unless I am in too high a gear and then brake just
long enough to get into a lower gear so the engine brake will hold.

Perfect!

Re: Running in the mountains in the morning

Reply #23 – June 09, 2019, 11:39:42 am

Came down Sherwin Grade to Bishop yesterday. Think it is 8 miles long. Stayed in high gear (4th) all the way. I don't like to exceed 55 downhill on a grade with curves so I used 5 seconds of service brakes 3 times on the way down. Jake Brake is switched on all the time and did the job perfectly.

P

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