Has anyone done any checking to see if a cetane improver helps or hurts fuel mileage? I have been putting the AMS/oil cetane improver in my CRD and it seems that the fuel mileage has gone down a bit. Is the engine not working hard enough to utilize the better fuel or is it just that the weather has been cooler and the CRD seems to be very sensitive to outside temperature ?

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05 White Limited CRD
Weather Tech Mats (throughout), Fumoto valve, replaced thermostat @ 75,000, Yellow Samco hoses, 2nd generation OEM fuel filter head, Amsoil air filter, Firestone Destination A/T's, GDE Eco Tune, Timing belt & Water pump replaced @ 105,000 miles, Sears P1 battery

The higher the cetaine the faster the burning starts with out a lag. To compensate for lousy 40-45 cetaine fuel, the timing can be advanced a little to compensate for an engine that was designed to run on 55 cetaine. All non OEM tunes advance the timing to compensate (GDE more than Inmotion or Rocketchip) for the crappy US/Canadian cetaine. You tune most likely has the timing advanced to the point where boosting the cetaine of the fuel you use has a neglable effect on fuel economy. If you had a tank of crappy 40 cetaine fuel, the Amzoil cetaine boster may increase your mileage a little.
I use Amsoil oil in my engine and I carry a bottle of Amsoil cetaine booster for when I have to use lousy fuel when no better fuel is available. For general use with a fuel that I know the quality is OK and to better lubricate my CP3 pump and provide a mild cetaine boost, I use Walmart outboard 2cycle oil.
Keep in mind a fuel that produces the best fuel economy with an Inmotion Stage II tune or Rocketchip tune may not produce the best fuel economy with a GDE Eco Tune. When driving habits/conditions and local environment are the same, it all boils down to timing advance and cetaine.

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2006 Pearl Green CRD
Magnaflow 2 1/2" Cat Back
KJ Extra Leg Room Brackets, Carter Lift Pump, V6 Airbox, ORM
Fuel cooler, Oil Separator, Progard 7
Gauges EGT Boost Trans Temp Oil Pres, Michelin LXT AT2 245 70 R16
7,000# Draw Tight hitch, PML EX Deep Trans Pan
Centrifuge, SunCoast, Transgo, RAM TCM, InMotion Stage 2
Wife's 99 TDI VW Beetle

I think it is Snake Oil, It may work but with extra cost you will gain nothing. I use Power Service in the winter if I have to use unknown fuel, this is to keep it from gelling. I true higher cetane number should give you better mpg. It must not be a requirement to post that number I have never seen it here in WI.

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2006 Jeep Liberty CRD
1998 Beetle TDI Malone Tuning Stage 2
2001 Dodge Cummins
2005 Dodge Cummins
ASE, OBDII / VAG-CAN scaner / Service Manual

Mine starts better and in the winter here that means a lot.
I splash Powerserve grey in with 1 oz/gal 2 stroke from Walmart $12.15/gal
Every once in a while crappy diesel shows up, towing, hot, cold weather, why not?

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'06 Jeep Liberty Sport CRD with: GDE Hot Flash and Tranny Flash, ehm, Cummins fuel pump, 3" Magnaflow muff, Moog K3199's, Skids, 225-75-16 10 ply, OME springs, Euro T/C, Shift kit, Trans cooler w/thermal bypass, Bigboy bkt, Samco CAC, Brake controller, Trans temp gauge, Al's Upper Arms

PowerService grey gives me 1-2 mpg better - however whether that's cost effective - is a solid maybe....

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2005 CRD
stuff
Skeptic quod gratis asseritur, gratis negatur

So.... if you consistantly fill up at one particular station, you can fiddle with the quantity and brand of fuel additive to optimize your results. The higher quality the fuel you start with, the less effective your fuel additive will be? With the warmer weather coming here in Arizona, will the need for cetane improver increase or decrease ? If one were to add more airflow ( ie GDE turbo kit ) would the increased "boost" require better fuel or allow higher cetane rated fuel for potentially better fuel economy ?

For every 10 gallons of petrodiesel I add 4 ounces of 2 cycle oil, 3 ounces of PS gray or white depending on the season, and 1 ounce of Diesel Stabil. Don't know if it helps, but it eases my mind when I think about rebuilding a $10,000 motor. Like most lubrication issues, you only see the difference at the END of the service life. I expect my pump and injectors will be working longer than most.

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Grid power- the one true essential

2005 Liberty CRD- ARP studs, Fumoto, Hayden FC, inline Tstat, ETechno 7v GP, Platinum P1, in-tank lift pump.
1983 Volvo D24T
1981 Volvo D24
Dodge Cummins TD
Case 580B
Mitsubishi MT180 diesel
Kubota BX25 diesel

Well, cutting back on the cetane improver in my Dodge has netted me a measureable improvement in mpg. So tommorrow the CRD gets a fillup with a little bit of biodiesel ( 1/2 gal )and some Power Service instead of a big slug of AMS/oil cetane improver and a big slurp of Power Service and we'll see what happens. Whoooooo ya ! This is FUN !