8.9L Cummins 450hp ? Hot with Black Soot ? WTH? (this is not short)

[Kim (skyking4ar2) Bertram]

When our coach was delivered to us in Salt Lake City last year, it had about 2,000 delivery miles on it. As we rolled on out over the hills to Oregon, we often noticed a burned smell, a little like something electrical but not that acrid, when pulling a hill, wafting through the coach. We could go in the rear bathroom and it was obvious it was coming from the engine bay. Never smoke, just an odor.

We stopped in California at a Cummins service center for a 5,000 mile check for the transmission, and had oil and fuel filters changed out on the 450 hp version of the Cummins 8.9 ISL. I asked the service tech about the smell, and if it had anything to do with the Diesel Exhaust Fluid used in this engine. He said he did not find anything amiss when he was underneath and that it should burn off. He said there was a burn in period on that exhaust system. I thought 5,000 miles should have burned in anything that needed burning.

Well, here we are at 10,000 plus miles and it hasn?t. Shortly thereafter, I bought the SilverLeaf software to track the computer outputs, especially after a check engine light came on climbing a grade in northern California. I also started monitoring the engine temp and trans temp on the Freightliner dash module as I was driving.

I noticed we would run some high (seemed to me) trans temps when climbing (over 180 degrees) but then learned that was well within the operating range.

All of this background leads to an incident recently climbing the San Juan Mountains out of Taos. Most of the way up the last grade, the engine temp light came on, the engine temp showed 212 degrees, and as I was slowing, the stop engine light came on, the engine derated, and then stopped. A low coolant indicator came on, but checking the coolant, it was at the top of the filler reservoir, just where it always is.

We unhooked the toad, the ambient temps were in the 50?s, let the engine rest, then pulled on over the top of the grade, and rehooked at the bottom of the grade. On we went, same song, different verse another couple hundred miles in to Utah.

The temp gauges running around 1400 RPM which is our normal cruising range at 55 mph, will typically run 170-185 on engine temp and roughly ten degrees lower for trans temps. When we hit a decent grade, or long grade, the engine temp will start clicking up to 200 or so, and if we keep hitting the grade, it will climb to 210 or so. What I noticed, was, that once we top the grade and start down, especially when the engine brake comes on and runs the engine up to 2000 RPM, the engine temp will drop 20 to 30 degrees in an instant.

Finally, we go into the bathroom at the end of this adventure, and there are soot streaks on the mirrors, at the door jambs, dusted in to the shower, and craziest of all, inside the dryer on the tub fins!

I believe the soot and the engine temps are roughly related, i.e. when it is pulling hard, it is pushing soot (hopefully out the tail pipe) and that is the source of the smell. I am also wanting to believe that somehow, the water pump or radiator fan is related to a speed sensor, and that is why the engine temps fluctuate wildly.

Now it?s your turn, if you have some Cummins engine owner experience, to weigh in on the two issues ? where is the soot coming from? And why are the engine temps wildly fluctuating?

And, yes, we are headed to Cummins Coach Care Center in Salt Lake City after Moab.

 

[taoshum]

Water pump?  Thermostat?  The instant cool down seems like a big clue.... faulty thermostat might not fully open when hot and might not fully close when it cools down...no expert though!

 

[Gary RV_Wizard]

The cooling fan is controlled by the Engine computer, in response to a number of parameters. Engine temp is obviously one, but the same system also cools the incoming air (Charge Air Cooler - CAC) and the dash a/c. Plus it is hydraulically driven, so it shares the available hydraulic pressure with other demands.

If the soot is coming out the exhaust pipe, the toad will be coated with it. Is that the case? I'm thinking you have a leaky exhaust manifold or a break where the pipe runs under the engine bay. That lets soot get sucked up into the coach somehow. What bathroom was coated - is it a rear bath?

Obviously engine load drops when going downhill. The engine brake pushes the rpms up, but no fuel is being burned and temps should go down.

 

[Kim (skyking4ar2) Bertram]

@Taos - Gary - not knowing the system yet, if the water pump is engine driven, I would expect temps not to peak, but rise and fall with flow. In this case I would expect a sticking thermostat, unless it is also electronically controlled and getting bad information. If the water pump is not gear driven, like my LT-1 Chevy patrol car was, and electronically sensed, there's a suspect, again a bad sensor. I actually had that happen.

@ Florida - Gary - I like the leaky exhaust manifold but have not been down the engine hatch or under the coach in the gravel. The toad has had a bit of a film from time to time, but not the soot. The soot is in the rear bathroom which obviously straddles the engine. It has appeared in every area that would pass air around the engine room, including the inside of the rear bay doors as if there was some low pressure area in the rear of the coach.

We will be up in Moab in two weeks, concrete pads, and lots of Forum geniuses. We may turn this into a happy hour project. At least I will feel better yakking about it with a beer in my hand.  8)

But seriously, soot in the dryer which is closed??? that makes me wonder about the dryer vent on the upper rear side above the tailpipe... many clues, possibly more than one issue...

 

[Spudnut81]

Kim,

From attending Camp Freightliner, I learned that the "sweet spot" for the Cummins ISL is about 1750 rpm.  Also, when going up step grades is was recommended to keep the rpm's above 2000(for power and proper cooling).  I believe you may be lugging the engine too much.  No help on the soot issue.

 

[huntnski]

Kim, don't have any answers for you, hope things clear up for you. Thanks for putting me in touch with Wendy, she helped a lot. Off thread question, what hiway did you cross mountains on, we will be going through Tao's on our trip and eventually crossing on hiway 50. I would offer mechanical advice, but I'm still learning which end of my MH my motors in.

 

[Gary RV_Wizard]

On  my ISL the water pump is engine driven - belt driven right off the main drive pulley. The thermostat is the standard bi-metalic type and opens at 185 degrees. That's a late 2003 edition ISL in a 2004 Freightliner XCM (modular) chassis. The fan for the radiator and CAC is not belt driven and is variable speed under ECM control. It starts running at about 115 degrees and increases speed as directed. I'm told by a Freightliner factory tech it is PWM control, but not quite sure what PWM means with a hydraulic fan. Maybe the solenoid that gates the hydraulic pressure to the fan is PWM-controlled to regulate the available hydraulic pressure.

1750 would be fairly high for my ISL, even though that is the peak horsepower point (peak torque is much lower, around 1300).  I cruise at around 1600-1650 most of the time and that gives me around 62-65 mph. Definitely not lugging and I don't think you can "lug" as long as you are between the peak torque and peal HP points.  Besides the engine ECM, in combination with the Allison ECM, is managing the rpms vs power demand. It is pretty much impossible to cause lugging, even if you select the wrong gear. It simply ignores choices that would cause problems and up/down shifts. On any sort of grade, though, the engine ECM puts the tach firmly at 1750 and lets the Allison choose the gear that fits best.

 

[Kim (skyking4ar2) Bertram]

Roger,

I have read that 1750 number before, and while it may be the sweet spot for horsepower, I thought my engine was maximum torque at 1400 rpm, a little higher than Gary's but that can be discovered in the book.  I can try the 2000 rpm on grades, too. I am pretty confident the computer can manage the shifts better than me, so I usually leave it alone and it does fine. I pulled Tehachapi Pass last summer at 55 mph with nary a whimper on cruise, but I will give you that this sounds like a classic lugging issue or even the wrong shift points.

I will have to check my gearing at 1750, but on the flats, that's probably way too fast for my tastes. 62 mph has always been my mark for better ride and control, and certainly fuel mileage. We got in the habit of 55 mph in California with the tow limits, and it seems fine.

We'll have a chance to tach it up at the end of the week when we move up to Blanding, UT from Bluff and pull a couple of hills at altitude. I'd rather discover it was my driving habits than a mechanical issue.

And I still have to find the source of the soot... :'(

 

[Spudnut81]

Kim,

I have found that I get better mileage on 2 lane roads when I drop the transmission down to 5th when I am on those roads and like to run in the 58 to 62 area.  I especially notice the difference if you have to fight the wind.

 

[Kim (skyking4ar2) Bertram]

Latest report - today we moved 25 miles (mostly uphill) and I altered my driving habits to incorporate some of the earlier advice. I manually shifted the hills to keep the RPM's up and there was noticeable difference in the way the temps responded. It is important to note, though, we did not tow the Honda because of the short haul.

There were several long grades, and on the steepest, I got the low coolant annunciator again. It went off over the hill, and the temps stayed right at 200 degrees, no higher, which is different behavior. They did not tach right up like they had been doing - they moved slowly like an engine trying to keep itself cool. I did not notice the soot or the smell on this trip, but we may not have been on the road long enough, either.

When we move to Moab next week, we will have another opportunity because there are a couple of good pulls to get there in the next 70 miles. The final chapter is yet to be written.

 

[Kim (skyking4ar2) Bertram]

The final chapter after relocating up to Island Park, Idaho, and pulling some grades from Moab on the way is that changing driving habits has all but eliminated both the black soot and most of the temperature issues.

Insuring that the RPM's are up around 1700 on grades, and punching down a gear when the temps start climbing hard to kick the fans in around 2000 RPM on the big hills have forced the temps to be more reasonable.

 

[Chet18013]

There have been several discussions on other forums about temps, climbing, torque, and HP. The general consensus is whenever climbing a long grade, force the engine to downshift and get the RPMs up in the 1900-2000 range. This will actually make the engine run cooler. It is especially true with the high torque diesels that are available in the larger class A coaches. Running them at the peak torque rpms rather than the peak HP rpms produces much more heat.

Using the higher RPMs when climbing forced me to make a change in my driving habits, but has certainly reduced my engine operating temps in the mountains.

 

[Kim (skyking4ar2) Bertram]

Running them at the peak torque rpms rather than the peak HP rpms produces much more heat.

I might not have believed that until I was specifically told that by Freightliner and then I saw it with my own eyes on the gauges. I would have also thought running at peak HP would have impacted my fuel mileage, but that does not seem to be affected.

 

[Ernie n Tara]

Kim,

We have the smaller diesel so results are not directly comparable, but I watched closely (because of this thread) when we pulled Wolf Creek pass Saturday. Water temps reached 212 and the trans got into the 190's. This was mostly at relatively high rpm's (2000+) and speed in the high 30's and 40's because of the road. At no point did I get any indication of problems.

If I were you I'd have the radiator cap and/or the system pressure checked. The only way I can think of (other than a computer problem) to get the low water indication you mention, with full water, is boiling the water in the reservoir. Water at 10+ psig, 18-20 psia?, does not boil at your reported 212 F.

Ernie

 

[Kim (skyking4ar2) Bertram]

Ernie,

We actually did have a low water issue. I did not read the opaque tank clearly.

Your numbers were almost identical to mine using the new driving technique.

We are pretty sure we are past the major issues.

Kim

 

[Becks]

Kim....I do not mean to sound rude, but I think you have learned what many have known for years. Simply down shift as needed to keep your RPM,s at 2000 when climbing steep grades and you will go up without problem. But do not forget to keep your radiator clean. Enjoy.

 

[Kim (skyking4ar2) Bertram]

My other coach did not have this behavior at all with a 300 Cat. The computer and cruise control never failed me and it never lugged or got warm. The only time I had to manually manage it was on extremely steep grades.

I feel certain the gearing and the programming on this model are materially different and require a different driving style which we now have.

 

[Gary RV_Wizard]

I'm shocked, though, that any driver management is needed for rpms on a late model rig. The transmission and engine ECM should manage that by themselves, and should do a better job than you could ever do on your own. I think you need to get the programming re-calibrated so that the shift profiles are correct for the weight, axles and tranny gearing.

 

[Kim (skyking4ar2) Bertram]

Well, that's what I knew from two years in the other coach, Gary. The Cat made a lot of racket so you pretty much could hear where you were, but this one is so quiet, you don't get a sense of the lugging unless you glue your eyes to the numbers.

I was always suspicious of the shift points, but now I am doubly so. Possibly getting some recorded metrics from the VMSpec will help the diagnosis. I have no clue how they parameterize their programming, but will be asking some questions of the Freightliner folks. We have some scheduled maintenance here shortly and that would be something I'd like to get verified.