[turbodiverart]

Hey all,

Towed for the second time with the truck, 5500# - 6000#, 24' enclose car trailer. The first time I went out I left the truck in drive (not manual) and not tow mode. I was monitoring my EGT's and I believe I remembered my EGT's being in the 1000+ range most of the trip. I had registered about 13 MPG.

This past weekend I towed back to the same location but this time I had the truck in manual 5th the whole way. I don't like tow haul because of what I feel is the ineffectiveness of the exhaust brake with such a heavy load. Just doesn't seem to slow me down but it certainly tries revving the engine north of 4000 RPM's. I will say that I likes towing in manual 5th. Held the gears better and the mileage was pretty good averaging 14.5 to my surprise. The other thing I noticed was that my EGT's were significantly lower this trip. I averaged EGT's in the 800's. The unfortunate byproduct of the lower EGT's is that my soot levels went up from 30% to 80% on my 130 mile round trip. I had thought the EGT's would have been high enough in the 900-1000 range to passively burn out the soot from the DPF. Now I know the truck will have to do another active regen soon.

With the local racetrack opening up I'll have to monitor and play with towing in 6th to see if I can get higher EGT's and burn the soot out and also to see if the lower mileage towing mostly in 6th was just a fluke.

 

[alberta minimax]

Interesting results.
You are moving more air through the motor, with lower temps so soot will be higher.
Keep us updated Please.

 

[turbodiverart]

I had originally thought that. The first time I towed up to the track was to try out the truck towing my trailer and that was in March shortly after buying my 2017 truck. Although I don't know the air temp that day, I would say it was probably a little cooler than on Sunday when it was 74 and sunny. One thing I do remember from the first tow was that it was damp, misty and drizzled a little during the tow. I would think the moisture in the air would have kept EGT's lower acting as a natural water injection but who knows, certainly displacing oxygen. I would say even if the temps were cooler the barometer was definitely lower on the first tow vs Sunday's where the air was very dry.

I'll definitely be doing regular towing to the track this summer so I can try different stuff out and gather more data. I do think having the truck in 6th gear and lugging the engine will create higher EGT's but we will see.

 

[Coloradorob]

I also use manual mode and I believe the crazy downshifting and high RPM is not good for the engine. I also use manual 5th as I noticed at 6k lbs my truck never shifts to 6th anyway.
last year I didn’t have a monitor connected but this year I do. I was hoping the regens would be passive with a load on the engine.
i do notice that while on the highway my soot levels actually drop even without a load.

Rob

 

[turbodiverart]

I test towed again trying 6th gear to lug the engine and although my EGT's were highest in 6th with the converter locked up I just couldn't get the EGT's high enough to passively regen. I think I'm regening less than once a tank, probably averaging in the high 300 low 400 mile range. But it's tough cause I just have not been doing much highway driving except for towing.

 

[18Z71Minimax]

I also use manual mode and I believe the crazy downshifting and high RPM is not good for the engine. I also use manual 5th as I noticed at 6k lbs my truck never shifts to 6th anyway.
last year I didn’t have a monitor connected but this year I do. I was hoping the regens would be passive with a load on the engine.
i do notice that while on the highway my soot levels actually drop even without a load.

Rob

Not to be rude, but you're wrong. There's absolutely nothing wrong with the engine RPM coming up to provide engine braking and engage the exhaust brake.

These engines have so much emissions crap on them it very literally requires catastrophic failure to break them. A stuck injector. A manufacturing defect in a rod or piston. Regardless of manual mode or not, you simply can't make these engines function in a dangerous way.

Don't believe me? Put it in manual mode at 70 mph and keep hitting downshift... You'll never make it to first gear, I promise you.

 

[18Z71Minimax]

Also... The rotating mass of these engines is rated quite high. They don't rev that high because you can't burn diesel fuel completely that quickly.

But have a look at the internals... They're not like the diesels of yore with pistons that weigh a couple pounds each.

If I'm not mistaken, the rotating assembly on these is capable of something like 6k.

 

[Coloradorob]

Also... The rotating mass of these engines is rated quite high. They don't rev that high because you can't burn diesel fuel completely that quickly.

But have a look at the internals... They're not like the diesels of yore with pistons that weigh a couple pounds each.

If I'm not mistaken, the rotating assembly on these is capable of something like 6k.

View attachment 8821

Sorry man but I think these are not built that well. And a big problem with reving a diesel is that the high pressure pump is mechanically connected to the engine. And with today’s diesel fuel having low lubricity the last thing you want to be doing is spinning it any faster than necessary. Or cycling poorly made injectors getting a lack of lubrication from today’s fuel any more than absolutely nesesary .
its not just the rotating assembly that you need to be thinking about.

Brakes are cheap and easy to replace. And my trailer has brakes too. So why would I want to rev the crap out of the engine? Sorry man but this back pressure idea for Diesel engine braking is one of the stupidest I haVe come across.
I would use it if it wasn’t so aggressive with the rpm . But the way it is ......no thanks..

And the transmission programming is so poor it’s unbelievable.
Even without a trailer there is days my truck will do the engine braking when just normal driving around the city.
Other days it doesn’t do it. Same route same speeds. Can’t figure out why.

I really like my truck and I like the diesel option, especially here in Canada where diesel is cheaper than gas.
But unfortunately I have no faith in the quality of this engine.
I pull 6k and am very impressed but I am not going to press my luck reving the crap out of it for no reason.
On my truck the exhaust brake does very little to slow down my 6k load...

Rob

 

[bigoilbob]

"And the transmission programming is so poor it’s unbelievable."

Interesting. Mine's great on my 2018. Yes, I do occasionally push 4 grand, but not often, or for long. To each his own, but I'm going to over serve my truck and trust GM engineering otherwise.

"On my truck the exhaust brake does very little to slow down my 6k load... "

Same total load, I'm guessing on mine. We've pulled with 5000+ in the trailer, and a packed bed and back seat, for over 20K miles. Much on Canadian "highways" that are sub Arkansas secondary road quality. And my engine braking is just fine, in conjunction with early use of a combo of vehicle and properly adjusted trailer brakes. I especially like how it works in trailer tow mode, and cruise control. Helps to keep an Uber space cushion around, with regressive driving habits...

 

[turbodiverart]

Again, to each his own! I'm with Rob that I don't like the exhaust brake on our little 2.8, others may like it. I will differ with Rob in that engine and exhaust braking does work. I have friends who have the 6.6 Duramax and Cummins diesels and the exhaust brake works very well. Big rigs have been using Jake brakes and exhaust brakes forever and they clearly work. Engine/exhaust braking works very well when it's effective.

I, like Rob, tow a fairly heavy trailer. Mine is in the same range as Rob's, 5500-6000 lb range (I've never weighed the trailer). It's a 24' enclosed steel constructed car trailer that houses my racecar. For that weight the engine braking just creates RPM and really doesn't slow things down, going down a hill it absolutely does nothing for me. When I come off exit ramps it may slow a little but it's not like my friends with 6.6's and Cummings engines where they barely touch the brakes and you can feel the engine slowing the truck/trailer down. For me when I've tried it with my 2.8 I tap the brake once, then again to get it into like 3rd gear where the RPM's are like 4000 and it still doesn't slow me down. I end up having to hit the brakes harder than I would have if I was not trying to let the exhaust brake work. The little 2.8L just doesn't have enough displacement to slow down 10K combined weight. If it was not so aggressive I would probably use it but for me spinning 4,000 RPMs for no real benefit just doesn't make sense. Regardless if spinning 4000 RPM's while braking doesn't do any damage, it's not adding life to the engine so why do it?

An excellent comparison I can personally give. For over a decade I towed this same trailer to the same track using my 99' Suburban K2500 with the 6.5 turbo diesel (weights over 7500 lbs fuel and tools). There is no exhaust or engine brake. Using cruise control with the converter locked up, I can de-accelerate using the "de-accel" button on the cruise control and my non exhaust brake 6.5L diesel at 2200 RPM's will slow my trailer faster than my 2.8L Colorado at 4000 RPM's and the Colorado weighs almost 2000 lbs less! I can't tap the brakes with the Suburban because doing so will unlock the converter hence the need to use cruise control. The old adage is true, "there's no replacement for displacement".

 

[bigoilbob]

"I would probably use it but for me spinning 4,000 RPMs for no real benefit just doesn't make sense."

I agree that doing something for "no real benefit" is silly. But if I were you, I'd get my system checked, We all have similar tows, but I get plenty of "benefit" from my engine brake. Even well below 4 grand....

 

[turbodiverart]

Maybe but I wouldn't know what to request other than, "I don't think my Exhaust brake does much". LOL.

You can fell it trying to do something and maybe I'm just expecting too much. In my 6.5 I can feel a distinctive push when I de-accel. With the Colorado I don' really feel much other than the RPM going up, the drag it creates is very minimal for me. Maybe I'm just expecting too much. Besides, with it off I'm barely using the trucks brakes as it is as I generally let the trailer slow me down vs. having it push my truck.

 

[scarfile]

I also use manual mode and I believe the crazy downshifting and high RPM is not good for the engine. I also use manual 5th as I noticed at 6k lbs my truck never shifts to 6th anyway.
last year I didn’t have a monitor connected but this year I do. I was hoping the regens would be passive with a load on the engine.
i do notice that while on the highway my soot levels actually drop even without a load.

Rob

They're happiest running hard.... Was designed to.

 

[FFPaul]

I’m surprised no one has mentioned that in tow haul mode the goal is to keep the torque converter locked up to reduce transmission temperatures and reduce wear on the transmission. Locked in 5th or sixth gear the transmission must unlock making extreme heat. The transmission won’t make many miles abused like this.
I have towed a tractor that was all of the rated tow capacity from California to Montana over many grades. With cruise control and tow haul mode I averaged 20mpg with speeds as high as 75mph. The trailer was rock solid and exhaust brake worked great slowing to cruise control speed as we went down the grades.
My take is use the truck as it was designed and you have good results. Ymmv

 

[turbodiverart]

OK, so I’m getting some strange regen data going on, I may have to go in for that recall to see if it helps.

I’ve been tracking regens for a past few times. I wasn’t too worried before as I have not been doing any real highway driving so I expect it to regen rather frequently. With almost all in-town driving, lots of stop and go and short trips I seem to be regening about every 170 miles. Where I think I’m concerned is that I also build up soot in the DPF while towing. This past weekend when towing to the track I started my trip at 24% soot load in the DPF. Mostly highway or state route driving. Highway is at 70 MPH for about 30 miles and state route is about 50 MPH for another 30 miles with a handful of stoplights. By the time I got to the track my soot load had steadily risen from 24% to 78% in 60 miles towing 5500-6000#. My sensor 1 bank 1 EGT’s are usually in the 800’s occasionally going into the 900’s while cruising depending on if I hit a small hill. Bigger long hills I’ll get into the 1100’s. DPF EGT’s are close behind the post-turbo EGT’s. On the drive back I was expecting to perform a regen but my soot load for the 60 mile trip back only rose from 78% to 90%. The track is about 600 foot elevation from my home but that’s not really that much compared to what lots of you tow. Going home is technically downhill but honestly not that much, NJ is mostly flat. I’ve noticed similar results when towing to South Jersey where it’s completely flat the entire way. I don’t know if I’m just blessed with lower EGT’s, they are reading wrong or I really need to get the DPF programming flash recall done.

A few additional observations I can share for you to chew on. Rain isn’t your friend. I’ve noticed that the DPF EGT is significantly cooler when it’s raining. Makes sense as you are splashing water under the truck. On the highway I see in dry conditions that the DPF EGT is only about a hundred degrees or less cooler than EGT sensor 1, bank 1 which I believe is the EGT immediately post turbo and other than the EGR EGT should be the hottest reading. That’s after the truck is completely warmed up and you are cruising on the highway for a while. I observe the same when towing. Tip: if you have to do a regen while city driving pull it into manual and keep the RPM’s between 2000 and about 2300. Doing this seems to complete the regen in about 25 minutes as opposed to 20 on the highway. The DPF EGT when driving is still reading above 1100 degrees but drops when stopped. I want to do another test to see if just driving with lower normal RPM’s has the same regen distance but I suspect not. Another observation and I have no tuning data to back it up but I seem to see higher Sensor 1, bank 1 EGT’s during a regen. I didn’t think the engine tune changed other than maybe closing the EGR. Maybe during regen it supplies a little less boost or a little more fuel at cruise to richen up the engine mixture to raise engine EGT’s.

 

[Coloradorob]

OK, so I’m getting some strange regen data going on, I may have to go in for that recall to see if it helps.

I’ve been tracking regens for a past few times. I wasn’t too worried before as I have not been doing any real highway driving so I expect it to regen rather frequently. With almost all in-town driving, lots of stop and go and short trips I seem to be regening about every 170 miles. Where I think I’m concerned is that I also build up soot in the DPF while towing. This past weekend when towing to the track I started my trip at 24% soot load in the DPF. Mostly highway or state route driving. Highway is at 70 MPH for about 30 miles and state route is about 50 MPH for another 30 miles with a handful of stoplights. By the time I got to the track my soot load had steadily risen from 24% to 78% in 60 miles towing 5500-6000#. My sensor 1 bank 1 EGT’s are usually in the 800’s occasionally going into the 900’s while cruising depending on if I hit a small hill. Bigger long hills I’ll get into the 1100’s. DPF EGT’s are close behind the post-turbo EGT’s. On the drive back I was expecting to perform a regen but my soot load for the 60 mile trip back only rose from 78% to 90%. The track is about 600 foot elevation from my home but that’s not really that much compared to what lots of you tow. Going home is technically downhill but honestly not that much, NJ is mostly flat. I’ve noticed similar results when towing to South Jersey where it’s completely flat the entire way. I don’t know if I’m just blessed with lower EGT’s, they are reading wrong or I really need to get the DPF programming flash recall done.

A few additional observations I can share for you to chew on. Rain isn’t your friend. I’ve noticed that the DPF EGT is significantly cooler when it’s raining. Makes sense as you are splashing water under the truck. On the highway I see in dry conditions that the DPF EGT is only about a hundred degrees or less cooler than EGT sensor 1, bank 1 which I believe is the EGT immediately post turbo and other than the EGR EGT should be the hottest reading. That’s after the truck is completely warmed up and you are cruising on the highway for a while. I observe the same when towing. Tip: if you have to do a regen while city driving pull it into manual and keep the RPM’s between 2000 and about 2300. Doing this seems to complete the regen in about 25 minutes as opposed to 20 on the highway. The DPF EGT when driving is still reading above 1100 degrees but drops when stopped. I want to do another test to see if just driving with lower normal RPM’s has the same regen distance but I suspect not. Another observation and I have no tuning data to back it up but I seem to see higher Sensor 1, bank 1 EGT’s during a regen. I didn’t think the engine tune changed other than maybe closing the EGR. Maybe during regen it supplies a little less boost or a little more fuel at cruise to richen up the engine mixture to raise engine EGT’s.

I been watching my soot levels for a while.
i find anything below 65mph and the soot level climbs like crazy.
if on the highway and the soot level is above 70% it will actually drop or stop climbing.
if the soot level is low it will climb even if on the highway.
at speed of 50 or less the soot level climbs very fast.
If I fill the truck and never get on the highway it will do almost 2 regens per tank. If i spend time on the highway I will get approx a tank and a third before a regen.
Rain really lowers the temp of the DPF and soot rises very fast as it can’t hold any heat with water splashing and cooling it off.
I was thinking that the down pipe and the DPF should be rapped to help hold heat for winter driving.....
I been avoiding the recall. It’s only to set a check engine light if the truck regens to often.
There is no code that will change how often it regens.
Also ...... during a regen the mixture is richer to cause a higher egt . The high egt is what causes the DPF to get hot enough to burn off the soot.

I have a Kabota tractor with no DPF and with today’s low sulfur fuel I never see any black smoke from the exhaust. So why are the DPFs on our trucks filling up so fast??????

Rob

 

[turbodiverart]

If I fill the truck and never get on the highway it will do almost 2 regens per tank.

I have a Kabota tractor with no DPF and with today’s low sulfur fuel I never see any black smoke from the exhaust. So why are the DPFs on our trucks filling up so fast??????

Rob

I think I'm probably seeing close to what your seeing so I feel a little better. Truck just did another regen, again 170 miles between.

I agree, since ULSD I can see it in my 6.5 TD's fuel filter. With LSD it uses to be totally black after 10,000 miles and even with LSD I'd get some black smoke out the tailpipe when towing, even when I had the soot trap in place. Now with ULSD the fuel filter doesn't look dirty at all, I have long removed the soot trap and even when standing on it I can't get any smoke.

 

[turbodiverart]

I have to add that I do find it strange that it seems to build up soot on the highway while towing at about the same rate as just cruising. I've tried towing at 65 MPH, 70 MPH and even 75 MPH, in 5th gear and 6th gear (which mine seems to hold just fine) and the soot build up is about the same. I know some on here see their soot levels go down while towing. Not sure if that's with a tuned truck or stock. Just think it's strange. My EGT's while towing are only a couple hundred degrees higher than just cruising. Just think it's strange. Generally flat towing.

I am towing my trailer light (maybe 4000 lbs) out to Ohio on Rt 80 which has hills thru PA most of the way so we will see how it does. My thoughts are the EGT's should be high enough to burn soot on the long uphill side and it'll be basically cruising the downhill sides. It'll be interesting to see if it performs a regen on the 450 mile trip out.

 

[DeeK]

I’m surprised no one has mentioned that in tow haul mode the goal is to keep the torque converter locked up to reduce transmission temperatures and reduce wear on the transmission. Locked in 5th or sixth gear the transmission must unlock making extreme heat. The transmission won’t make many miles abused like this.
I have towed a tractor that was all of the rated tow capacity from California to Montana over many grades. With cruise control and tow haul mode I averaged 20mpg with speeds as high as 75mph. The trailer was rock solid and exhaust brake worked great slowing to cruise control speed as we went down the grades.
My take is use the truck as it was designed and you have good results. Ymmv

I am confused by your sentence "Locked in 5th or sixth gear the transmission must unlock making extreme heat." It sounds like keeping torque converter locked in 5th and 6th by using tow mode should reduce hear. What do you mean by "must unlock", what would cause this?

 

[SFLTruck]

I can see the TC lock up and gear on my Banks I-Dash. The TC locks up in 2nd gear and never unlocks in 3rd through 6th even when towing 6Klbs. So as DeeK questioned what does "must unlock" mean....