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Cummins M11 at Altitude

October 11, 2016, 04:08:10 pm

Question: what impact, if any, does altitude have on the Cummins M11 in our coach? Ditto for the PowerTech 10K generator (3-cylinder Isuzu)? 

I did a Forum search for "diesel and altitude," but ended up in discussions of Detroit Diesels versus Cats and Cummins, as well as 2-stroke versus 4-stroke. Reading further, I did find an interesting thread on the PowerTech 10K generator and hard starts, but that seemed (?) unrelated to our experience this trip.  So . . .

Cummins M11:  Now that we're in the West and plan to remain here a while, we're seeing altitudes we haven't driven before (7,888 ft at Raton, NM, campground). That's not high compared to some of the passes we expect to go through in Colorado, but the Raton Pass is what prompted the question. I don't spend much time looking out the driver's side mirror, but did notice once during this trip grey-to-black smoke from the M11 exhaust. Have never seen that.

PowerTech 10KW Generator:  We had an experience very similar to this one posted to ForeForums. Our generator has always started and run like a champ (doesn't mean it will do that forever or without care, I do realize!). But the very rough start and a lot of gray smoke was new. Again, altitude or . . . ?

With thanks!

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Re: Cummins M11 at Altitude

Reply #1 – October 11, 2016, 04:28:34 pm

Altitude will always affect the engine off boost - especially at startup. Your turbo makes a huge difference feeding the M11 more air at high altitudes, but at low boost or during startup an increase in smoke is to be expected. The generator will produce less power but unless you are running at or near maximum output, you shouldnt notice any actual difference.

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Re: Cummins M11 at Altitude

Reply #2 – October 11, 2016, 05:27:55 pm

Small puff of light black smoke on heavy throttle applications at altitude.

Noticeable power loss at high altitude.  Like all diesels.

Max boost lower.  26?  Noticeable torque loss in upper gears and medium throttle application.

As we got back to low altitude the change in power was very apparent. Max boost 30+

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Re: Cummins M11 at Altitude

Reply #3 – October 11, 2016, 11:04:22 pm

Find the hp plot for your engine (it should be in the user binder, or look it up online with CPL). Most that I have seen from cummins say they will make rated HP up to 5,000 or 6,000.

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Re: Cummins M11 at Altitude

Reply #4 – October 11, 2016, 11:20:56 pm

A few engines long ago held sea level power to 7,500 feet.  Most, as stated, start dropping off at 5k feet.

There was a factor from long ago about altitude loses.  Never seen one for a m11.

The butt dyno feels like 20% loss at 10k feet altitude.

Which feels like much more versus the needed power just to move the coach.

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Reply #5 – October 11, 2016, 11:56:05 pm

I have the 10KW PowerTech with Kubota on my 94 Bluebird.

Here is what I found in the past:
Load, fuel gal per hr
> 25% .256
> 50% .412
> 75% .912
> 100% 1.00

10KW (10,000 watts)= 83 amps theoretically avail
- derate 1% every 10 degrees F over 68 degrees
- derate 3.5% per 1,000 ft above 500 feet altitude
5,000 feet altitude = 68.75 amp or 8250 watts
- gen runs at 1800 rpm

Comparison:
"true" 50 amp shore power = 12,000 watts (split on 2 legs)
30 amp shore power = 3600 watts
20 amp shore = 2400 watt, 15 amp = 1800 watt

On transfer switches: With sources of 110 volt the priority scheme is:
If you have inverter on, generator on, and plugged into shore power as well (why we would I don't know)
Generator has priority 1
Shore priority 2
Inverter priority 3.

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Re: Cummins M11 at Altitude

Reply #6 – October 12, 2016, 12:20:06 am

Can't supply hard numbers , but as you approach summit of vail pass you will feel like your toad has tripled in size !
Best example , get out of coach at rest area and take  brisk walk up incline

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Reply #7 – October 12, 2016, 05:07:06 am

No real issues climbing and driving out west.  The turbo solves that problem but you will run hotter in the summer if it is hot out at altitude as the fans pull less air has been my experience.  I travel there every year and no issues.

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Reply #8 – October 12, 2016, 09:39:46 pm

I'm in Phoenix and run up to Flagstaff (7000ft elevation) all the time and have no problem in performance. Summertime though when temps are high I keep the speed below 65 mph and run in fifth gear to keep the radiator happy. I obviously I have more engine then the radiator when ambient temp is over 105 degrees.
Steve

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Reply #9 – October 13, 2016, 12:34:41 am

The Eisenhower tunnel is over 11000ft above sea level, turbo diesel suffers less than NA gas engine but still suffers loss of power

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Reply #10 – October 13, 2016, 01:55:06 am

Our last 30,000 miles in our M-11 have been flat-landing mainly. No real smoking at start or load ever, until...

The Teton Pass out of Jackson changed elevation pretty fast and we saw some "light black puffs" under throttle, until we got "back down." No problem later, the puffs quit as we descended. I was concerned at first, searched the forum and relaxed a bit. Pretty tough, old climbers, these! Our 10KW Kubota never sneezed.

Floor it...(if visibility, road conditions and equipment allows.}*

* lawyers

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Reply #11 – October 13, 2016, 01:58:05 am

I operated my 1996 UU320 and our current 2005 U320T in the mountains and parked at our house at 7500' with little problem.  The main caveat is try to avoid having to move coach from a standstill on an major uphill incline especially towing anything. There is little torque until you get to 1000rpm and that can be hard to achieve on a steep grade. I got caught once having to stop on a steep grade and I thought I was going to need to remove toad to get uphill.

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Reply #12 – October 13, 2016, 11:23:18 pm

This is a situation where having a free flowing exhaust helps immensely.  After removing muffler and installing resonator turbo spool up is several times faster, eliminating those black puffs pulling away from lights in Santa Fe.

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Reply #13 – October 13, 2016, 11:50:54 pm

Steve that's why I comment on owners pulling over on grades because they are maybe overly concerned about the temp gauge.

Had the same long term issues with my owners back in the 80's.  Took a lot of personal drives up grades to instill confidence that they were not damaging their coaches.

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Re: Cummins M11 at Altitude

Reply #14 – October 14, 2016, 01:56:11 am

My personal experience with starting on a grade is ta my house in the mountains.  I back out of the driveway and have to drive uphill to turn around.  In my case I am able to back far enough to get to a lower grade incline that allows me to develop rpm before I hit the steepest grade.

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