Fuel EconomyDear Ole Mechanic;

I've been looking at new trucks to see if any of them would get me better fuel economy.  I am currently driving a small 2004 extended-cab truck with a 4.3 liter engine and automatic transmission.  I'm looking for a full-sized truck rather than a smaller one, because I'm going to be pulling a two-horse trailer part of the time.  I'm also looking for a two-horse trailer.

Some of the dealerships that I have visited have mentioned ‘MDS’ and ‘FFV’ as ways to save fuel.  I didn’t want to appear dumb, but what are ’MDS’ and ‘FFV?’  How would they help my fuel mileage?

Looking and Confused

Dear Looking Confused;

Let’s get a couple of things straight.  A full-sized truck will not get as good a fuel mileage as a smaller truck, simply because it weights more and takes more fuel to move this additional weight.  When you add even more weight by hooking on a two-horse trailer, you are going to burn even more fuel. 

If you have not purchased the horse trailer yet, then you can keep from burning more fuel by purchasing one made out of aluminum rather than one made out of steel.  Less weight in the trailer means less fuel to tow it.

Now to your question about ‘MDS’ and ‘FFV.’  FFV  (Fliexible Fuel Vehicle) indicates that the truck can burn E85, regular gasoline or any combination of the two.  E85 is a mixture of 85 percent ethanol and 15 percent gasoline.  I'm not sure why any dealership sales representative would say that a FFV vehicle would increase your fuel mileage, because the ethanol has fewer BTU’s of heat content per gallon than gasoline.  Since the heat content is what produces power to move a truck, you will use more gallons of E85 to move a given weight than you would gallons of gasoline.  E85 does make use of renewable American resources to make ethanol; therefore, less oil is imported from abroad.  Also, ethanol comes from renewable sources such as corn and other things that can be fermented into alcohol.  Yes, E85 is 85 percent corn liquor, but don’t try to drink it, as the 15 percent gasoline tastes like crap and doesn’t do your innards any good.

MDS (Multiple Displacement System) can save fuel.  MDS is just a different programming of the engine ECM (engine computer).  It works by sensing the load being placed on the engine.  If the load on the engine is light enough to be handled by four of the eight engine cylinders, then the computer stops delivering fuel to four of the cylinders.  Using four cylinders under light load conditions saves fuel.  When the load increases, the computer returns to a full eight-cylinder operation and power.  This system was developed by Cadillac in the late 1970’s or early 1980’s as a 8-6-4 system.  The electronics at that time were not as good as today’s engine computers, and there were some complaints, as the change from eight to six to four cylinders could be felt.  While the new truck’s computer is a lot better, a change from eight to four cylinders and back may be felt but in the face of $3.00+ per gallon gas prices, it feels good to be saving fuel and people are more willing to accept it.

Will MDS save fuel while pulling a horse trailer?  NO!  You will be pulling a heavy load and the engine will need all eight cylinders to pull that load.  Will MDS save you fuel when not pulling a load?  Possibly, but it will depend upon your driving.  If you have lead in your right foot--Nope.  If you drive it easy, then Yes, you might.

I have a suggestion.  Why don’t you ride the horses and leave the truck and trailer at home?

Herr Professor Nuzanbolts