If you own an '07.5-newer diesel vehicle then you understand what the term "regeneration" means. In short, it means crappy fuel mileage and insanely-hot exhaust gas temperatures.

 I towed my boat to Lake Havasu, Arizona and back last weekend for a quick family boat trip. The temperatures were a mild (for Arizona in the summer) 115-degrees. I have to idle the diesel a lot to run the A/C for the wife and kids while waiting at the boat launch, fuel fills, restaurant take-out runs, and so on.

Normally idling wouldn't present a problem, but modern diesels like mine are laden with Nox and DPF filters that collect soot and other stuff from the exhaust so nothing but invisible vapor with a mild chlorine-smelling undertone escapes. As the DPF fills with soot, the ECU triggers a "regeneration" cycle during which raw diesel is injected into the engine on the exhaust stroke. It's kinda like an afterburner in a jet and increases the EGT to between 1,100-1,300 degrees to burn off the soot inside the DPF.

My big problem with trips like this is for a regen cycle to complete you really need to drive your truck at highway speeds for 30-40 minutes. And that just doesn't happen when you're in a little river town in the middle of nowhere. I do have a high-idle feature on my truck, which I activate during idle time. It helps prevent the DPF from filling too quickly, but it doesn't prevent it. So, after a weekend of boating bliss, I hooked my trailer, loaded the family, and headed back to home. As soon as the truck hit 50 mph I watched the EGTs climb to 1,150 degrees as the regen cycle kicked on...then climbed to 1,200...then briefly to 1,300..then it settled down around 1,150 for a good 45 minutes of driving time at 60 mph.

I stopped in Parker, Arizona to grab some drinks from the cooler and hit the road again...and the regen kicked back on. It was like my truck was taking a massive dump or something. Finally, a couple hours later shortly outside of Desert Center, CA the regen stopped. I pulled over to in Desert Center before hitting the I-10 to grab some more drinks out of the cooler and I found one of my NAPA mudflaps had been torched by the exhaust gas temps.

I find it kinda funny and kinda scary but man, think of the fuel wasted to make all that heat.