With common rail diesel engines becoming the normal, engine manufacturers have been advising extra vigilance on diesel cold flow issues.
While the cloud point temperature does vary from fuel batch to fuel batch (in other words, no two fuel s are exactly the same), most ultra-low sulfur diesel fuels have a cloud point in the 20s. That’s not a concern very often for users in the South, but up north, it very much is. Cold flow treatments are effective at preventing diesel fuel gelling as the temperature drops below this, but only if they’re added to the fuel before the wax appears – when the fuel is warmer than the cloud point temperature.
Engine manufacturers are now telling us that this old protocol isn’t satisfactory anymore, because the fuel filters installed on common rail engines have tighter tolerances. They filter out smaller particles than ever before (to protect the valuable common rail system).
In the past, these fuel filters went down to 10-20 microns. This means the largest particles allowed to pass through the filter were between 10 and 20 microns, which is 10-20% the width of a human hair. Engine manufacturers are currently requiring fuel filters rated at 2-5 microns, to protect the advanced engines to a much greater degree.
Smaller filter ratings mean that the fuel will effectively cause gelling problems at higher temperatures (sooner) than before. How much higher temperature? The ballpark estimate is 10 degrees higher, which also happens to be the general temperature difference between a diesel fuel's cloud point and its cold filter plug point.
So if your diesel fuel has traditionally caused gelling issues at 20 degrees, you now need to plan for those issues at 30 degrees. If your local temperatures are already headed that way, now is the time to take action to prevent cold weather engine problems. These temperatures are already there in many parts of the country. Once the temperatures drop below those points, it will probably be too late.
Cold flow polymers are the only viable protection to prevent fuel gelling. But since there's so much variability in fuel properties, it's hard to know which is the best to choose. At the large scale level, cold flow improvers can be matched to the fuel properties by analyzing the wax distribution and determining what combination of pour point and cloud point depressants will work best for the specific refined diesel stock being used.
Consumers - fleets, stored fuel users, municipalities - can also rely on these kind of aftermarket cold flow protection packages. These are more along the lines of one-size-fits-all, but are formulated to give the broadest protection across the most possible kinds of fuel.