Interesting diesel regen observation

Yesterday I did 400 miles, mostly at 60-75mph,in my 150bhp UK diesel. At the start of the trip I reset the average fuel consumption.

Not sure why, but I check it quite frequently. Around the 50 mile mark, I was averaging 51mpg. Shortly after it plummeted to 45 and I realised it was in a DPF regen cycle.

The final average consumption at 48 by the end of the 400 miles.

Only mildly interesting but, to those in the US who are about to get diesels, you might find this useful to know ahead.

Ziggity said:

Yesterday I did 400 miles, mostly at 60-75mph,in my 150bhp UK diesel. At the start of the trip I reset the average fuel consumption.

Not sure why, but I check it quite frequently. Around the 50 mile mark, I was averaging 51mpg. Shortly after it plummeted to 45 and I realised it was in a DPF regen cycle.

The final average consumption at 48 by the end of the 400 miles.

Only mildly interesting but, to those in the US who are about to get diesels, you might find this useful to know ahead.

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Are there any indicators on the instrument cluster to let you know it was in REGEN?

mazdadude said:

Are there any indicators on the instrument cluster to let you know it was in REGEN?

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Not on my late 2014 CX-5 170bhp diesel, nor my previous 2015 Mazda 6 170bhp diesel, nor my neighbour's 2016 Mazda 6 150bhp diesel, nor his previous 2015 and 2014 Mazda 6 170bhp diesels.
The only warning you get is the current (and average) mpg plummeting for a good few mins. Also I get an occasional puff of white smoke under moderate acceleration, and the exhaust note changes on the over-run.

On Australian models, the only regen indication on the dash is that the iStop light goes off. Comes back on when cycle is completed. Does it not do that on UK models??

Depending on how well tuned your ears are to things automotive, you will also notice a change in the engine note. The owner's manual mentions that too.

And I would also confirm that what Ziggity described is typical of when the regen cycle happens. Of course, the mileage change is far more noticeable if you have just refilled your diesel tank and reset average fuel economy monitor. The flip side is that if you have used half a tank or more, the average is naturally not affected as much.

Moonlighter said:

On Australian models, the only regen indication on the dash is that the iStop light goes off. Comes back on when cycle is completed. Does it not do that on UK models??

Depending on how well tuned your ears are to things automotive, you will also notice a change in the engine note. The owner's manual mentions that too.

And I would also confirm that what Ziggity described is typical of when the regen cycle happens. Of course, the mileage change is far more noticeable if you have just refilled your diesel tank and reset average fuel economy monitor. The flip side is that if you have used half a tank or more, the average is naturally not affected as much.

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Yes, the Stop stops working which is often the first indication. The “NOT READY” sign on the fuel economy monitor shows and yes the engine note changes. This new model did it today for the first time at 240 miles which is a huge improvement over the 100 miles of the 2016.5. The trouble was that it was raining and with the car5 being so quiet I couldn’t hear it but I will have a good listen next time.

Moonlighter said:

On Australian models, the only regen indication on the dash is that the iStop light goes off. Comes back on when cycle is completed. Does it not do that on UK models??

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Mine is the pre-facelift model with the older style NB1 stereo with the volume button on it rather that down at the commander. There's no iStop light lit during normal driving, but it lights up yellow/orange if you disable the iStop for a journey. I pretty much always have mine disabled, but I'm pretty sure the same light goes green if iStop has shut the engine down. There's no specific indication that a regen is happening.

My previous 2015 Mazda 6 had the newer infotainment style stereo, and the iStop light behaved the same, but there was a screen on the infotainment you could choose with info about how many trees you've saved etc. One part of that had an iStop indicator which changed to "not ready" if a regen was occurring, but it also went to "not ready" for other reasons - IIRC when you had just started the engine, or the battery was slightly low, or you had a drastically different outside temp to inside, or you had the heater set to screen. Either way - it wasn't dependant on only a regen occurring.