The secret to improving your diesel fuel mileage!

Ah yes, the magic to getting better fuel mileage.  I get this call quite often.  First we have to understand what fuel mileage is.  Fuel mileage is getting the most power out of every drop of diesel fuel.  What makes one drop of fuel work better than another?  Quality is one factor.  Fuel needs to be burned to make power.  The proper mix of fuel, air (oxygen), and heat is needed to make fuel burn.

I am a Boy Scout and have built many camp fires in my day.  To make a fire you have to light the wood.  Putting a match on a log does not work.  Trying to light damp wood does not work.  A match produces a small amount of heat and can therefore only light something small, like paper.  Once you get the paper lit it makes more heat.  The extra heat can light small sticks.  That extra heat can light larger pieces and so on.

Fuel is the same way.  Poor quality fuel takes more heat to burn, and larger fuel droplets take more heat to burn.  Using a quality fuel additive raises the cetane number which makes the fuel burn easier and improves fuel mileage.  Worn out injectors spray larger fuel droplets than new injectors.  We recommend Stanadyne Performance Formula.  It is a great year round fuel additive that pays for itself in additional mileage and the rest of the long list of benefits it provides does not cost you anything.

Ok, so using a quality fuel additive will increase your mileage enough to break even on the cost.  That is not what most people want for better mileage.  So here is the rest of the story…

A diesel engine makes power and torque across a wide RPM window.  The power and more importantly the torque is what pushes your truck down the road.  The peak torque on most pickup trucks is below 2000 RPM.  In that 1800 to 2000 RPM range the engine is more efficient at burning diesel fuel.  As the RPM rises over 2000 the torque droppes off and your mileage does too.

This is where horsepower comes into play.  Let’s use an early Duramax engine that makes roughly 300 horsepower.  Driving around empty and keeping the RPM under 2000 will average 16 miles per gallon.  Now that same truck loaded with a large trailer can drop to 12 MPG or less.  The reason is the additional load on the engine needs more horsepower to maintain the same speed.  The truck empty may only need 250 horsepower to go down the road.  When the truck goes up hill more power is needed which is not a problem because there is 50 more horsepower available.  Now that truck loaded down needs more like 275 horsepower or more until it hits that hill.  Then it needs more than the available 300 horsepower to make it up the hill.  So what happens?  The transmission down shifts, ask someone who drives a stick shift.  Dropping to a lower gear gives the truck a mechanical advantage to get up the hill.  When the transmission down shifts the engine RPM goes up over the ideal 2000 and mileage drops off.

So the answer is power!  Yes horsepower is wonderful unless you have to pay warranty bills for the engine.  Manufactures are smart and they only give us enough power for what the engine can safely handle.  Remember the fire analogy?  Well to make power we need to burn fuel.  Burning fuel creates heat.  Too much heat melts your pistons.  That is the reason for EGT gauges.  Monitoring exhaust gas temperatures is the key to how much additional power you can safely run.  The rule of thumb is do not exceed 1250 degrees of exhaust gas temperatures for more than 30 seconds or so.  A good combination of upgrades include airflow improvements.  Start with the exhaust system so the heat is not bottle necked in the engine.  Next improve the air intake system to allow air to get into the engine uninterrupted.  Better airflow reduces EGT’s and allows you to run higher horsepower safely.  That is the ticket for better fuel economy.  Make enough power to not have to down shift and have the ability to run under 2000 RPM as much as possible.

Everyone has different needs and goals for their diesel car, truck, or RV.  You can count on Huckstorf Diesel to sell you what works and not a bunch of hype.  There is no magic “Mileage Tune” out there.  The manufactures do their best to optimize their engines for mileage while staying compliant with the stringent government restrictions.  If there was something simple to improve mileage they would be doing it.