[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