AAMCO - Which Gas Should I Use?Diesel

It is first of all crucial that you understand that a Diesel engine car can only use Diesel. You have no other options. Period. Most people already know this but we just want to make sure that nobody accidently gets the wrong impression.

Follow Directions

As car specialists, we know that the easiest way to keep your car in good shape is to follow the factory recommended products to maintain your car. However, you have probably heard somewhere that using a cheaper octane level of gasoline than what is recommended is alright. The answer to the question is really up to you and though we recommend the car manufacturer’s choice of gas for your car, we will go over why there are different types of gasoline and why some cost more than others.

Regular, Mid-Level, Premium

Most gas stations in the U.S. have three tiers of gas and each grade comes with a different number. These numbers refer to octane ratings, and with higher octane levels come higher prices. But is an octane rating? To most people it simply means: higher number better gas, but why is it better to have higher octane?


An engine can only work in the proper conditions. The most important variables that makes sure an engine works efficiently is the combustion ratio and operating temperature. Every engine come with a minimum octane rating, which calculates all the variables that allows an engine to work correctly. Usually car manufacturers do not recommend the minimum amount of octane to use for your car engine however. Think about it, the minimum amount of anything can get you a passing score, but if you want to make sure that the heart of your car keeps ticking longer, you should be doing more than the minimum.


If you get less than the minimum amount of octane required for your engine, then your engine will “ping”. When your engine has the right amount of octane gas as its fuel, then it can control combustion correctly. However, when your octane levels are too low, then the gas will combust uncontrollably within the cylinders and this is what we call a ping or knock. You DO NOT want your car to ping. Pinging can severely damage your car engine and kill it over time.


Let’s say that your car’s manufacturer recommends that you use a Mid-Grade octane level of gasoline. However, as your engine gets more wear and tear over time, you may experience pinging even though you have been using the right octane level gasoline the whole time. This is when you should use a higher grade of gasoline. The longer your car is used, there will be carbon buildup within your car’s engine. This will increase the combustion ratio of your car, which will also increase the octane rating of your engine. An older car may have been running fine on the fuel you have been using for years, but suddenly your engine might start to knock. When your older car starts knocking, then use higher octane gas to stop this from happening and keep your car running properly.

Premium Gas

Though it is not always highlighted at the pump, premium gasoline usually comes with more than just a higher octane level. When premium gas is getting refined, it receives a better additive than regular. Though the contents of these additives are not clearly published to the public, it is usually a mix of solvents that keeps the fuel system within the engine clean.

Speculations On Modern Octane Ratings

There have been various studies that have been publicized on the media that questions the proper octane level to use for your vehicle. Some studies have found that most modern cars can use the lowest octane level gas that is available at the pump. Since we here at AAMCO Colorado did not conduct these studies, we believe that it is always best to follow the directions given by your car’s creator. If you decide to go with a fuel that has an octane rating that is lower than recommended, please make sure to do your research before and check your engine often.

Picking the right gas is part of maintaining your car properly so that it runs efficiently. Whether you are maintaining your car or repairing it, we here at AAMCO Colorado are here for you. Contact Us for anything related to your vehicle. We are engine and transmission repair experts with locations in Denver and Colorado Springs. See you soon!