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High Altitude Driving: How Does it Impact Your Engine and Gas Mileage?

BY: Dario DiGiuseppe
Red SUV taking a road trip through the mountains

America is a place like no other to own a car. Whenever the moment takes you, you can set off on a road trip and travel the entire country. But with such varied terrain, it’s more than likely that you’ll find yourself driving at high altitudes from time to time.

Combustion engines need oxygen to operate, so it would make sense that a lack of it might affect your engine and gas mileage (or MPG). How much, however, is what we’re here to investigate today. Let’s take a look at the science behind high-altitude driving and the impact that it might have on your vehicle.

The Basics of Engine Combustion

Combustion is the scientific term for burning, which is the basic chemical process of releasing energy from a fuel and air mixture. As the name implies, with an internal combustion engine (ICE), the ignition and combustion of the fuel happens inside the engine itself.

This is converted to energy via a fixed cylinder and moving piston. As combustion occurs, expanding gases push the piston, which turns the crankshaft. This then activates the vehicle’s powertrain, which propels it forward.

The two types of combustion engines currently being used in cars are the spark ignition gasoline engine and compression ignition diesel engine, which both differ in how they supply and ignite the fuel. For spark ignition gasoline engines, fuel is mixed with air and then inducted into the cylinder.

The piston then compresses the fuel-air mixture, and the spark ignites it, resulting in combustion. In a diesel engine, only air is inducted into the engine and then compressed. Fuel is sprayed into the hot compressed air at a measured rate, which causes it to ignite.

How Altitude Affects Engine Performance

During World War II, engineers were working on constantly improving fighter planes to allow them to fly at higher altitudes. The higher they went, however, the higher the air pressure got, the less oxygen was available for combustion. This ultimately led to the invention of the supercharger, which made air pumps engine-driven. With one of these equipped, planes could fly normally, even at extreme altitudes.

This is great for planes, but as most cars don’t have a supercharger installed, the problem of high-altitude “breathing” still affects them. Even with all of the modern bells and whistles cars often come with, nothing can alter the laws of physics, and less available air means a poorer fuel-to-air mixture. There is a little room for maneuvering, but mess with this delicate balance too much, and you’re bound to experience a few problems.

If you’re wondering why automakers don’t just put a supercharger on to their vehicles like a 1940s Hellcat, the answer is simple: money. Cars are designed to operate under an ideal set of circumstances right here on the ground—not tens of thousands of feet in the air.

While there are some very high-altitude roads around the world, it’s not often you’ll find yourself on one, and so the extra expense of designing a turbo or supercharger that kicks in when needed would just be a complex, unnecessary cost.

Implications for Gas Mileage at High Altitude

So altitude can wreak havoc on your engine, but can it affect your gas mileage, too? Unfortunately, the answer is yes, and it isn’t good news. This goes back to your engine being starved of oxygen, and as a result of there being less air to pull in, fuel isn’t burned as efficiently. On top of the lack of fuel efficiency, because your engine is generating less power, it needs to work even harder to perform at the level it’s supposed to.

But the gas mileage problems don’t stop at your engine. The higher you drive, the lower the temperature will be. This will affect a number of things, including your tires, which will lose pressure rapidly. They’ll still have enough air in them for you to be able to drive, but a lower PSI will result in more friction with the road. That extra drag will harm your fuel economy and could even lead to total tire failure if the pressure gets too low.

Other Altitude-Related Vehicle Concerns

If you thought the problems ended there, that’s some wishful thinking. The effects of altitude can also cause other concerns:

Loss of Horsepower

For a number of reasons, vehicle engine performance suffers at high altitudes. The rule of thumb is that for every 1000 feet, you lose 3% in horsepower. As a quick example, if your car has 300 hp, and you drive from sea level to the top of a 14,000-foot mountain, you’d lose up to 126 hp (42%) by the time you reach the summit.

Using the Right Fuel

The octane of your fuel is what prevents premature detonation in fuel (aka knocking). High-power sports cars use high-octane fuel because their engines can run at higher pressures. If you’re at high altitude, however, a low octane is better. Gas stations at high-altitude locations can have gas with octane ratings as low as 85.

Filling up on 85 octane fuel is all good while you’re up there, but as you start to come back down, your car’s octane requirements will return to normal, and it won’t be too happy about it. Your only option is to use up the low-octane fuel while you’re at a high enough altitude or have a service center flush the fuel system for you.

4 Tips for High Elevation Driving

Highway leading to a mountain viewYou probably won’t be driving at extreme altitudes too often, but it helps to know a few tips in case you ever find yourself up in the mountains of California, Colorado, or Washington:

1. Prepare your vehicle.

Driving at high altitude puts a lot of strain on your vehicle, so take some time to make sure it’s in top running condition before you head out. This could involve carrying out some DIY maintenance tasks or taking it to your local auto shop for an inspection and tune-up. You really can’t put a price on added peace of mind.

2. Keep an eye on your PSI.

Tires start to lose pressure the higher you go, so if your vehicle has built-in tire pressure monitoring, keep a close eye on the PSI. Carry an electric pump in your trunk, and you can top up as and when necessary. Just remember that you may need to let a little air out on your descent.

3. Carry octane booster.

If you top up on low-octane fuel and can’t quite use it all before you head back down, you should always carry a bottle or two of octane booster, just in case. This will increase octane ratings by 2.5%, which is just enough to bring that 85 octane back up to the standard 87.

4. Invest in an extended warranty.

With all of the strain that high altitudes put on a vehicle, it isn’t uncommon for breakdowns to occur. This is potentially quite a dangerous situation to find yourself stranded, as high places often go hand in hand with extreme weather. With a good extended warranty watching out for you, roadside assistance will come to your rescue, and your bills will be covered at the auto shop.

Modern Technology and Altitude Compensation

It’s hardly a standard feature, but some vehicles do come with a turbo or supercharger installed. If you own one such vehicle, you might not notice much power loss at high altitudes — if any at all. Of course, your car is still susceptible to all of the other issues caused by high-altitude driving, but by forcing air into the engine, the turbo/supercharger allows your vehicle to compensate for the altitude and overcome atmospheric differences.

What Is an Extended Auto Warranty?

They might not all have superchargers, but there is one thing that absolutely every vehicle has in common: they start life with a factory warranty. Factory warranties are effectively the automaker’s promise to repair or replace any parts that fail due to fault within a predetermined number of years/miles traveled. Once this expires, however, you, as the owner, are fully responsible for any future repair bills.

Traditional extended warranties, also known as auto protection plans, allow you to continue the coverage past the expiry date, but they come with two big caveats. The first is that your factory warranty must be active to purchase a traditional extended warranty — leave it just a day late (or buy a used vehicle), and you’ll no longer qualify. Secondly, all repairs must be carried out at a dealership, which isn’t ideal should you break down hundreds of miles away from one.

For these reasons and more, the vast majority of people prefer what’s technically known as a vehicle service contract from a third-party provider. Third-party providers have an incentive to offer almost as comprehensive coverage at an even better price point. They often throw in some great additional perks, and you can have repairs carried out at any certified mechanic. Vehicle service contracts can also be purchased regardless of factory warranty status.

Why Endurance Is Your Top Choice for Extended Auto Warranties

Even if you don’t push your car to its limits, it’s an unfortunate fact that all components fail eventually. When the worst ultimately happens, you don’t want to find yourself stranded at the roadside — much less up a mountain — and faced with an expensive repair bill that wipes out your bank account. To protect themselves (and their wallets) from the cost of unexpected mechanical breakdowns, drivers nationwide are investing in auto protection plans. And Endurance is your top choice.

Highly rated by industry experts and customers alike, we’ve helped many drivers save serious money on the cost of car ownership. We offer a wide range of plans, with options for casual commuters, rideshare drivers, select luxury car owners, and even high-mileage vehicles. And if our base packages aren’t quite what you’re looking for, our award-winning customer service team will be more than happy to put together a bespoke program that suits your specific needs and budget.

We don’t just offer market-leading coverage. Our value-added perks are some of the best around. Every Endurance plan includes 24/7 roadside assistance, trip-interruption costs, and rental car reimbursement as standard. Better yet, all new Endurance customers also get a year’s free access to our Elite Benefits, bolting on extra services like tire repair/replacement, total loss protection, key fob replacement, and more.

Be Prepared for Any Driving Situation

Don’t leave yourself open to repair bills—make sure you’re covered with top-tier auto protection from Endurance. To find out more about what we can do to keep more money in your pocket, just give our customer service team a call at (800) 253-8203 for a FREE quote, or shop online today. If you’d like to do some more reading about all things automotive, we also have plenty more articles on our extended warranty blog.

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