Premium Fuel… What you need to know!

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I get people coming into the shop and talking with me all the time about their cars.  One of the things that honestly doesn’t come up very often is fuel.  I’d venture to say that most people think that premium fuel is simply better.  In a way I suppose it is but maybe not in the way you would think.  I’m here today to debunk the premium fuel myth and maybe confirm some suspicions that you might have about it.

So lets first get into the difference between regular (87 octane), premium (90-93 octane) and we will even cover a bit about E85 (yuk…). The main differences between premium and regular fuels are their resistance to self ignite and the additive package that the fuel manufacturer adds.  Regular fuel usually has very few if any additives that help to keep your fuel system and engine clean while most premium fuels will have detergent additives that honestly in my opinion are just marketing ploys to get you to spend the extra money on it.  Gasoline in itself is a great cleaner!

So what does this all mean and how does it apply to you and your vehicle?

I thought you’d never ask!!  You see, engines run by burning a compressed air and fuel mixture.  Air is drawn into the engine by pistons moving downward within a cylinder, similar to how one of those tube style water guns draw in water as you dip the tip in the water source and pull back the handle. While this air is being drawn in, a small mist of fuel is sprayed into air stream through the fuel injector and drawn into the cylinder with the air.  Once the piston is at the bottom of it’s stroke and it’s drawn in all the air and fuel that it can, the valve that let the air and fuel in closes and the piston heads back up in the cylinder squeezing (compressing) the air and fuel because the valve is now closed and nothing can escape.  This squeezing and compressing (known in the field as “compression”) creates a lot of heat and if enough heat is created, the air and fuel could ignite without the aid of the spark plug and before the piston gets near the top of its travel.  That’s where the fuel quality comes into play.

The fuel absolutely cannot ignite before the spark plug ignites it.  If it does this will cause a condition known as spark knock, or engine ping and that condition can be very damaging to an engine if left to continue.  Higher performance engines create more compression.  In other words to get more power they squeeze the air and fuel more.  Some production engines can have a compression ratio as high as 10:1!  That means if you start with 10 units worth of volume it will get squeezed down to just 1. It’s that extreme amount of compression and therefore heat creation that requires the use of premium or higher octane fuel so that spark knock doesn’t happen and tear up the engine.  Premium fuel resists that urge to ignite under high compression and heat better than regular.   For most gas engines on the road today, regular fuel is just fine and honestly using premium fuel will give you almost no benefit.  However, if you have a performance vehicle, and on your fuel door you see a sticker warning you to use premium fuel, you should.  That’s really it!  There isn’t any other reason to run it!

So the bottom line is this:  If the engine in your vehicle requires high octane fuel, use it.  It’ll run on regular, but you might unknowingly be doing damage to your engine.  If your vehicle doesn’t require it, don’t use it.  It’s not worth the extra cost as it will not provide any noticeable performance gains or power.  It MIGHT help keep things a little cleaner in there, but it is certainly no substitute for professional fuel and induction cleaning services that should be performed regardless of fuel type used at least every 20,000-30,000 miles and even sooner on a GDI equipped engine as there are places inside your engine that will suffer from carbon build up that do not come in contact with fuel to keep them clean, but that’s a topic for another day!  One more thing I should mention, if I don’t someone else will, some premium grade fuels do not have the “up to 10% ethanol” in them that pretty much all regular grade fuels do.  Honestly, I haven’t seen that much problem caused by the 10% ethanol in regular so I wouldn’t be worried about it.

Oh yea, I almost forgot… E85….  My professional opinion?  Stay away from it!  Especially if your vehicle is not a “Flex Fuel” vehicle. It’s tempting to use as it’s usually quite a bit cheaper, but I can’t tell you how many vehicles over the years have been towed to my shop after filling up with E85.  That’s right, some cars won’t even run on it!  And the ones that are designed to run on it see anywhere from a 3-7 MPG drop versus using regular.  E85 fuels can contain up to 80% ethanol which does not burn anywhere near the same rate as gasoline.  Flex fuel vehicles are equipped to handle this difference with extra sensors and programming to make the adjustments to the engine when this fuel is detected but fuel mileage will still suffer.

Till next time thanks for reading and as always you can find more info about my shop Auto Go Automotive Here!

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