2025 Cummins Regen Observations

[scdo]

I just made it back from my 700 mile trip from the dealer. While this is too early to be meaningful, I’m concerned on what I’m seeing.

Over the course of a 700 mile relatively constant 70-83 mph journey, I’m at 30% on the DPF gauge. Engine hours are approximately 17. I’ve also watched on my PID and can see that the soot load is slightly outpacing the engine hours in driving the % to regen.

My 2023 which had frequent regen problems (every ~120 miles around town) was able to keep to dash at 0% (after a fresh regen) on the other end of this journey.

Very surprised to see the brand new truck hit 30% but we also don’t know how the regen strategy on these operate yet.

Curious on others opinions but I’ll be updating my experience here. I’d also love to hear from other owners of the new engine.

 

[24Megacab]

How many idle hours were on it when you picked it up? I know when my 24 was delivered it had around 7-8 idle hours, if I recall correctly. I’m wondering if that’s the case with your truck, or if the 25’s just don’t passive regen as well? Congrats on the new truck.

 

[scdo]

Right now, there are 16 total hours, 4 Idle. I imagine 3-4 hours of idle before I started the 700 mile drive. DPF was at 0% at that time.

I would have thought any built-up soot would have been easily passively regen'd from that drive!

 

[24Megacab]

Right now, there are 16 total hours, 4 Idle. I imagine 3-4 hours of idle before I started the 700 mile drive. DPF was at 0% at that time.

I would have thought any built-up soot would have been easily passively regen'd from that drive!

I’d give it some time; wait til after your first regen and see how she does.

 

[AH64ID]

If the DPF gauge operates the same as 19-24 trucks then that is a little concerning, but time will tell if the gauge and regen strategies are the same or not.

 

[jharp]

I wouldn't be surprised if the baseline soot load is different (lower) for 2025. GM did this on the 2024+ L5P, they actively regen every 200 miles or so now. The regens are much shorter than before, but much more frequent. My 2024 L5P would let loose the grey smoke every 150-200 miles, but only for about 3-4 miles of driving. The duramax forum folks think this was done to extend the life of the DPF, rather than letting it get loaded with soot and risk incomplete burn off (like would happen on shorter trips) they regen more frequently, for a shorter duration of time.

 

[scdo]

If the DPF gauge operates the same as 19-24 trucks then that is a little concerning, but time will tell if the gauge and regen strategies are the same or not.

I haven't put many miles on it since returning to town but the DPF gauge dropped to 20% then back 30% - so it's definitely soot based as the older ones. That said, it's a close race of Soot vs Time... I'm like 76% to regen based on Soot and 75% based on time. Will be interesting to see when it actually regens and how it does on the next cycle. I'll keep this thread updated.

 

[scdo]

I wouldn't be surprised if the baseline soot load is different (lower) for 2025. GM did this on the 2024+ L5P, they actively regen every 200 miles or so now. The regens are much shorter than before, but much more frequent. My 2024 L5P would let loose the grey smoke every 150-200 miles, but only for about 3-4 miles of driving. The duramax forum folks think this was done to extend the life of the DPF, rather than letting it get loaded with soot and risk incomplete burn off (like would happen on shorter trips) they regen more frequently, for a shorter duration of time.

I don't know yet but the time-based regen appears to still be 24-hours based on how the PID values have changed.

 

[HarryN]

Right now, there are 16 total hours, 4 Idle. I imagine 3-4 hours of idle before I started the 700 mile drive. DPF was at 0% at that time.

I would have thought any built-up soot would have been easily passively regen'd from that drive!

Just curious - are your idle hours just running it to keep it warm while you work, or something else, such as warming it up before driving?

Do you put it into "high idle" when idling or just normal idle ? In theory, high idle is easier on diesel engines.

Thanks - just trying to understand how your use might compare to how I might use a truck.

 

[scdo]

Just curious - are your idle hours just running it to keep it warm while you work, or something else, such as warming it up before driving?

Do you put it into "high idle" when idling or just normal idle ? In theory, high idle is easier on diesel engines.

Thanks - just trying to understand how your use might compare to how I might use a truck.

I was actually very cautious NOT to unnecessarily idle and this was an all highway ride. That said, there may have been some idle time on it when I picked it up. I know it started with 20 miles but I’m not sure how many idle hours.

 

[Brutal_HO]

Just curious - are your idle hours just running it to keep it warm while you work, or something else, such as warming it up before driving?

Do you put it into "high idle" when idling or just normal idle ? In theory, high idle is easier on diesel engines.

Thanks - just trying to understand how your use might compare to how I might use a truck.

High idle reduces cylinder wash but creates more soot faster.

 

[HarryN]

High idle reduces cylinder wash but creates more soot faster.

Thanks

 

[HarryN]

I was actually very cautious NOT to unnecessarily idle and this was an all highway ride. That said, there may have been some idle time on it when I picked it up. I know it started with 20 miles but I’m not sure how many idle hours.

Does sitting at traffic lights count as part of "idle"?

 

[AH64ID]

Does sitting at traffic lights count as part of "idle"?

Yes, so does real slow speed driving in 19-24’s. So we’ll see what 25’s count.

 

[scdo]

UPDATE

I was out of town a bit and then only drove on a series of short trips (not ideal) after returning from the long trip from SLC to Phoenix.

Recap, over the first 17 hours (700 miles) I was at 30% on the DPF gauge.

From that point, I was able to make it to 23 hours, 48 minutes total before the first regen was triggered. DPF gauge was still only at 30% so I expect this was actually the 24 hour mark contrary to what Trip A showed.

The vehicle took 63 minutes driving to complete the regen (35 miles). This was a combo of high speed highway (not much), significant traffic, then city streets.

Interestingly, the EGT2 and 3 temps hovered around 650 the entire time in regen. My 2023 was more aggressive with temps running closer to 1,000. I find this surprising but maybe it’s better / easier on the system.

Let me know of any questions. Thus far I’m pleased to make it a full 24 hours eventhough I showed 30% on the dash. There was no sudden run/spike like I was seeing on the prior truck.

 

[superjoe83]

UPDATE

I was out of town a bit and then only drove on a series of short trips (not ideal) after returning from the long trip from SLC to Phoenix.

Recap, over the first 17 hours (700 miles) I was at 30% on the DPF gauge.

From that point, I was able to make it to 23 hours, 48 minutes total before the first regen was triggered. DPF gauge was still only at 30% so I expect this was actually the 24 hour mark contrary to what Trip A showed.

The vehicle took 63 minutes driving to complete the regen (35 miles). This was a combo of high speed highway (not much), significant traffic, then city streets.

Interestingly, the EGT2 and 3 temps hovered around 650 the entire time in regen. My 2023 was more aggressive with temps running closer to 1,000. I find this surprising but maybe it’s better / easier on the system.

Let me know of any questions. Thus far I’m pleased to make it a full 24 hours eventhough I showed 30% on the dash. There was no sudden run/spike like I was seeing on the prior truck.

Next time monitor the rear exhaust temp probes, they moved the DPF to the rear of the exhaust, where the SCR is on the pre '25 trucks, i bet you will see more activity on those probes

 

[scdo]

Next time monitor the rear exhaust temp probes, they moved the DPF to the rear of the exhaust, where the SCR is on the pre '25 trucks, i bet you will see more activity on those probes

Interesting, I was monitoring the same three probes as I was on my 23.

 

[Lerker]

Yah and if there is a seventh injector (is that now confirmed?), I guess it would make sense that EGTs wouldn't climb for a regen.

 

[AH64ID]

There is a 7th injector and I’ve read it injects just ahead of the DPF.

 

[scdo]

Yah and if there is a seventh injector (is that now confirmed?), I guess it would make sense that EGTs wouldn't climb for a regen.

They did climb but only to 650 F. That's more or less normal operating temperature... However, when slowing to traffic I could def see that the system was maintaining that temp even when driving wasn't conducive to it.