Additives are supposed the make up for the lubricating qualities that ULSD diesel lacks, help lubricate the fuel system, and raise the cetane rating a few points, and net you better fuel economy. All great benefits right?

Then why oh why does my truck run like crap and get WORSE fuel economy when I use them?!?!?!?

I normally use Power Service Diesel Kleen Gray bottle and my truck seems to like that...sometimes.

I just started using Howes "Diesel Treat" since Oreilly started carrying it, and although the idle is quieter, my power and fuel economy suffered.

I just topped off with normal diesel, no additives and my truck feels stronger and way more confident....

Can anyone explain this?

 

I think all those statements are arguable. But I'm still learning stuff so what do I know. I don't notice any improvement or reduced performance and I've tried several brands. I don't notice any mpg improvement whatsoever. I just use the stuff in the winter to prevent gelling.

 

The graphs below compare untreated #2 diesel (red curve) with #2 diesel that's been treated with the Amsiol Cetane Booster product (green curve) and I borrowed this picture from their web site. By examining the widths of and the areas under these pressure-time curves and the locations of the peak-pressures relative to TDC crankshaft position one can explain how using a DFA "might" increase or decrease the "HP" and/or "MPG"!

It seems to me that adding a DFA might increase the HP and/or MPG by increasing the area under the pressure-time curve and/or by effectively advancing the injection timing by shifting the peak of the pressure-time curve to a more favorable crankshaft position because either of these situations can potentially increase the amount of fuel heat energy that's converted into HP!



For a given amount of injected fuel the area under the pressure-time curve helps to determine the MEP=Mean Effective Pressure and the MEP helps to determine the HP and MPG! Adding a DFA to increase the cetane number of the injected fuel shortens the ignition delay interval between when the fuel is injected and when it auto-ignites. The effect of shortening this interval is to decrease the amount of fuel that's prepared to burn at auto-ignition so that when auto-ignition finally occurs the combustion event will be less severe. This results in a lower rate of pressure rise and a wider pressure-time curve with a time-advanced and lower value of peak-pressure.

The OEM injection timing is retarded from optimum due to emissions requirements and this means a DFA might increase performance by advancing the pressure peak to bring the timing closer to optimum. If your DP program already has adjusted the injection timing to its optimum value then adding a DFA might advance the timing too far and reduce performance!