Regeneration and Towing

[richp]

Hi,

I was trying to explain the regen system to my wife over dinner. Smart lady that she is, she immediately asked, "Will all that hot exhaust damage the trailer while we're going down the road?"

My fast answer was that if there was a problem like that, I probably would have read about it here. But it did make me wonder. Has anyone towing a fifth wheel with a DPF-equipped DMAX noticed whether the higher heat from the tailpipe is impacting the trailer? Or is the new tailpipe design dissipating the heat adequately under speed?

Thanks.

[DmaxMaverick]

Very good question. Kudos to your better half.

I have several friends with late Duramax trucks, and they haven't seen any heat damage or pealing paint/decals. The tail pipe outlet is designed to dissipate the heat. The angle of the outlet should also direct the heat away from the trailer, although at speed, the ram air would dissipate the heat before it could cause damage. There should be at least 6 feet between the tailpipe and trailer, which is more than enough to keep the heat off the trailer.

[afp2007]

My better half asked me the same question - the suggestion was made to purchase an aftermarket DPF back exhaust that discharges out the side. I am not sure if the airflow would dissipate heat better than the factory unit, or if the heat from the side exhaust would damage paint at the rear quarter panel.

A concern I have is that we use a grass skirt style tow skirt to reduce rock and gravel damage when towing on gravel roads. I suspect the regen cycle would melt some of the grass skirt filaments.

Comments?

Rick

[richp]

Hi,

Thanks for the quick responses.

Inasmuch as this is a fifth wheel, I may not have the six feet of separation that I'd get if it was a typical trailer. I'll measure it today, but I'll bet it's more like four.

Chevy says the temps are moderated by the design of the tip, and of course whatever airflow there is past the outlet will start to mix and cool it at once. But the more I think about it, I do wonder about hour after hour of exposure by the fiberglass, to what has to be somewhat elevated temperatures.

We're leaving for Florida with it a week from today or tomorrow, so I guess I'm going to find out. Full report to follow after the southbound leg....

Have a good one.

[Gapper_ca]

well a friend of mine has a 08 chev. he has the horsetail style of rock deflector on his truck. with the oem exhaust he has melted it away to nothing, where the exhaust pipe is. not sure about a camper if you have a 3-4 ft hitch or a 5th wheel. would hope that the gm engineers thought about that......
good luck ...

[MacDR50]

If you really want to check it out this link may help.

http://www.omega.com/ppt/pptsc.asp?ref=ML4C_LABELS&Nav=temf02

I would be interested to know as I have a fifth wheel and have yet to tow with my new truck.

[richp]

Hi,

I just went out and took a good look at my setup. The end of the exhaust pipe is dead even with the rear bumper. Worse still, it points straight back at where the front corner of the fifth wheel is going to be -- about two, and certainly not three, feet away from the tip of the exhaust outlet.

Jim Begley's article on the LMM says this, "This reduces exhaust temperature at the tip during DPF regeneration from 700-800°F to approximately 500°F."

I'm really concerned now -- 500 degrees will not be healthy for the fiberglass skin of my trailer. Even if it is down to 300 degrees after the air is mixed in at the other end of the tailpiece, I can't imagine long-term exposure will be free from some adverse impact.

Am I being a Nervous Nellie? Is there anyone out there who has been towing a fiver with an LMM truck, and can give some first-hand account of what happens under prolonged load?

Thanks.

[afp2007]

well a friend of mine has a 08 chev. he has the horsetail style of rock deflector on his truck. with the oem exhaust he has melted it away to nothing, where the exhaust pipe is. not sure about a camper if you have a 3-4 ft hitch or a 5th wheel. would hope that the gm engineers thought about that......
good luck ...

If you are anywhere near Regina, you can check with CloudRider.

I am either considering this, or the modified exhaust with side firing

[richp]

Hi,

I went to the dealer today, and they somewhat agreed it could be a potential issue. Chevy does not make a diverter or modified tip of any kind that would further direct the exhaust out or down. The owner himself has placed one call to the GM fleet testing manager, and is waiting for a second return call from the diesel testing component of GM in Detroit.

The more I wonder about this, two conflicting things run around in my mind.

1) I must be a "nervous Nellie" -- surely GM's testing of this exhaust setup and two years of towing experience by actual owners would have disclosed any problems.

2) I know (by my pyro gauge) that there are times going up long hills and mountain passes that the exhaust stream will reach 1000 degrees, and stay there for quite a while. Even if the distance down line from the turbo and the action of the venturi tip reduce temps by half or two-thirds, what effect will there be on the fiberglass of my trailer and the plastic underbelly, of sustained exposure to 300-350 degrees?

Anyone out there actually towing a fiver with an LMM who can give some first-hand info?

[MacDR50]

I asked this question in the Montana Owners Club forums and search a number of other ones. I have searched as many forums as I am able to find and the only RV related damage I have heard about is to the anti-chip skirts similar to that noted above. I really got into this subject and have been busy doing research. Here is a summary of my general findings on the DPF. If I have misunderstood or got something wrong I hope someone corrects me.

1. The DPF is found on all diesel road vehicles manufactured since 2007. All require regeneration.
2. There are two types of regeneration. "Passive" created by a catalyst in the exhaust system ahead of the DPF when the exhaust gases reach approximately 650F which should be no problem during normal highway driving or "Active" which involves a metered amount of fuel being added to the exhaust stroke (GM not sure how Ford and Dodge get the fuel in.) to bring the temperature in the filter up to 1200F.
3 During "Active" regeneration the temperatures at the tailpipe can be as high as 600F in the center of the exhaust gas cone. This temperature is reduced by the vented pipe extension that has a venturi effect caused by the speed of the gases coming out of the exhaust. This draws cool air into the exhaust gas stream.
4. As far as I can tell, all light duty trucks are now produced with or have a ECM reflash available that prevents "Active" regeneration during idle.
5. Active regeneration can use between 1.5 and 3 gallons(US)of fuel.
6. The colder the weather, the longer it takes to get the exhaust gases up to the required temperature. In "Active" regeneration this increases fuel consumption and the time required for regeneration to occur.
7. MDT and HDT are able to activate a manual regeneration at idle. I wouldn't want to be close to their exhaust when this was running.
8. Stop and go city driving will not normally allow a complete regeneration cycle and you will get a DIC warning. You need to take the truck for a 30-40 minute run at 50MPH or greater to allow regeneration to occur. If this isn't done soon, the ECM will put the truck in "Limp" mode. (30mph and 2nd gear??)

I don't run my truck fast or far enough. This might explain why my mileage is in the 10-12 mpg (imperial). This next weekend it gets a 600 km run at highway speeds.

[Kennedy]

At 30mph or better there will be enough wind mixing with the heat to keep you from having problems. While I would rather see the tip point directly out the side of the truck with say a 10° lay back angle, apparently all have gone to the back sweep deal.

[MacDR50]

I have taken out my infrared gun this week and shot temps at 3 locations in the exhaust: The DPF, the pipe before the tail pipe cone and the cone. Outside temps here are hovering just below freezing. Temps were taken after the engine reached operating temperature, with the motor running at idle.

DPF 354-680 F
Pipe 135-363 F
Cone 81-145 F

I expect that the higher temps were an indication of an interrupted active DPF regeneration. I wasn't able to get a good reading on the exhaust gas itself. Based upon my experience with other gases and fluids I would expect the centre of the gas cone to be hotter. I am going to try a few more tests particularily one after a long trip.

[richp]

Hi Mac,

Thanks for providing the first actual data I've seen. That's a great help to me.

But I'm not sure if I'm reassured or not. If the cone temps are in the same range as the gasses passing through it, things may not be as bad as I fear. Now if going up long passes and hills with 1,000 pre-turbo EGTs just aren't any worse than a regen....

I'm leaving on a 3000 mile, three week trip to Florida this weekend. Whatever happens will happen. I'll provide a full report on our return.

Have a good one.

[Rabbler]

The only trailer damage I've heard about occurred when an owner took off the stock cooler/tailpipe and installed an aftermarket chrome tip that pointed straight back.
As mentioned above an active regen while towing is unlikely (unless it was right on the verge due to previous city driving) because the exhaust will naturally burn off accumulated soot during the heavy load towing as the exhaust temp increases.

Make sure you only use CJ-4 rated oil and emission safe fuel additives.

I think you're good to go.

[richp]

Hi,

Well, back from about 3,500 miles of towing, and my apprehensions were totally unfounded. No sign of any over-heating of the front of the fifth wheel trailer.

Other impressions were positive. Towing stock felt comparable to my old LB7 with an Edge Juice. Hand calculated fuel economy was about what I got with the LB7 as well. I did get 13.4 once with a nice tailwind, but for almost all of the trip I got between 10-10.5 MPG with cruise set to 62 (1800 rpm in fifth). Unless I slept through it, the engine never regenerated. EGTs on the flat ran in the 7-800 range, and on long hills it held under 1250 -- again with cruise on.

So count me as a very satisfied LMM owner so far. Now if GM can just stay in business.....

[More Power]

That's good news! I wonder if it would be helpful to use one of those stick-on temperature strips (like they use on engine blocks) on the front corner of the trailer?

If the Banks advertising is the real deal, they claim their LMM exhaust temps at the exhaust tip are a little cooler than the stock pipe, and much cooler than the exhaust systems offered by other manufacturers.

Jim

[richp]

Hi Jim,

I actually put a remote temp sensor in the right-side compartment -- one that records max/min temps. It showed no appreciable rise over outside ambient conditions. Not quite the same as an outside temp strip, but still reassuring.

I confess I'm a bit surprised that there was apparently no regeneration over that many miles. But I suppose that's a benefit -- not a problem -- of towing. And with all the reports of lowered fuel economy in the LMM, the numbers I got seemed pretty good.

[MacDR50]

My understanding is that highway driving raises the filter temperature to about 650 and keeps it there. At this temperature you get passive regeneration (no fuel added to exhaust to create active regeneration).

Thanks for the report.

[Rabbler]

My understanding is that highway driving raises the filter temperature to about 650 and keeps it there. At this temperature you get passive regeneration (no fuel added to exhaust to create active regeneration).


You got it exactly right. At those temps any particulate will burn off from just the exhaust temp.
I have an acquaintance who hauls horses for a living with an 08 DMAX.
He has over 80k on his truck and it has never performed an active regeneration. Everything burns off from the extra heat caused by the towing.