Do they do anything? Are they a gimmic?

If there is no recommendation in the service manual for a DPF cleaner I would leave well alone.

The car has it's own system for cleaning the DPF, leave it be and let it continue to do its thing.

The manual makes a specific reference warning you not to add any additives to either the fuel or engine oil.

The car has it's own system for cleaning the DPF, leave it be and let it continue to do its thing.

The manual makes a specific reference warning you not to add any additives to either the fuel or engine oil.

Caution

It is not permitted to add the various fuel additives on the market, including petrol, to

diesel fuel in order to improve its flow properties

Above is the actual quote for fuel additives, it refers only to flow improvers which are still available and were only intended for use in extremely cold conditions before winter grade diesel was universal.

Modern diesel systems could be damaged with their use,never seen a confirmed report of this happening yet.

DPF cleaners are not flow improvers, if the vehicle is driven as per the manual and the information supplied by the dealer such cleaners are not needed, trying to back flush a DPF unit is also not a good idea.

Removing and re-programing the engine electronics can also cause other problems, an engine is designed to work with a designed back pressure in the exhaust system for optimum power and economy reducing this is not good practice.

Many boy racer types, used to buy and fit extra large diameter exhaust pipes and straight through silencers then come into our workshops complaing the vehicle did not go as well as it did, plenty of noise loss of fuel economy and in some cases power loss that could be felt just road testing the vehicle.

Some DPF cleaners do work, you will also find that many dealers add a fuel treatment on certain services, use premium fuel and drive as per the book and you should have no problems. Also remember if you try and obtain a new DPF under warranty, all regens are saved in the vehicles electronics this will be taken into account with any claims, it also gives a rough idea of the driving methods a large number of regens points to incorrect driving methods or type of fuel used.

I have less regens and 3mpg better fuel economy when using Millers Diesel EcoMax, compared to when I don't.

Jus' sayin'.

I added an STP NCT injector cleaner to a fill of diesel and then an injector protector on the second fill.

The motor is running great.

I have less regens and 3mpg better fuel economy when using Millers Diesel EcoMax, compared to when I don't.

Jus' sayin'.

I use millers ecomax too and have seen a similar increase in mpg. I can't say for sure how many passive regens I've had as it's often difficult to tell if you're on a motorway etc. I did have one yesterday-telltale fans going flat out when I'd switched off, but it completed it's cycle on the return trip (noticed the tickover higher than normal for the first few miles). I also tried an experiment on the way back not selecting 6th until I was doing 60 rather than change up as soon as possible and it made no difference to the mpg. I think the engine might produce less soot for the dpf to collect too as it responds quicker to slight throttle changes in a lower gear than I might normally take which would explain why I got the same mpg I guess.