Anyone who’s filled up a gas tank knows that you have to choose what kind of gas to put in your car. Why else would the options be there? When you have a high-performance car like the Volkswagen GTI, though, the decision is already made: the car knows what kind of gas it wants.
A VW GTI can run on regular gas, but it will end up costing more in the long run, as it provides worse mileage and can be destructive to the engine. Additionally, only premium gas will let it reach official horsepower and torque figures. High octane gas is best for maintaining the VW GTI’s engine.
Here’s why you should fill up your GTI with premium gas: how it’s ultimately more cost-effective, safer to use, and better for performance.
The Cost Issue
If you’re looking to save a few bucks, choosing 87 octane gas at the pump might seem appealing. Think again. While it might be marginally cheaper at the pump, the price difference is just that: marginal.
When you’re driving a GTI, fuel isn’t where you should be looking to save money. Cut down on costs somewhere else, like your eating out budget, and treat your car right. That way, it’ll last longer, ultimately saving you money by making the most of your initial investment in the car, as well as cutting down repairs.
There have been cases where people experiment with 87 as opposed to higher octane fuels. These were short-term experiments, though, and therefore can only account for immediate differences and not effects that take place over the course of years of using low octane gas.
The test run in California reported only mild reductions in torque and horsepower. They noted that greater differences may be observed at higher altitudes. The 87 had a worse fuel economy. (Source)
When you’re in a pinch for cash, it could be okay to use 87 octane gas in your VW GTI, but don’t make it a habit. Especially don’t make a habit of switching between the different octane, as doing this carelessly may lead to a nasty case of engine knock.
Different fuels ignite at different temperatures. 87 ignites before 91 does. That said, most engines are designed to be timed for when the fuel ignites. If the fuel ignites before the engine expects it to, then you get a ping sound, and that’s engine knock. It’s also called detonation or pre-ignition.
This happens while the fuel is in the cylinder. The thing that’s supposed to happen in the cylinder is the fuel mixes with air as the piston compresses it, and then the spark is supposed to ignite it.
Instead, what’s happening with engine knock is some of the fuel is burning the way it’s supposed to, but another part suddenly explodes, creating two flame fronts that meet and cause serious damage to your engine. This is incredibly expensive to fix, especially for a car like the GTI. (Source)
Now, the engines modern GTIs are able to adapt to different octane levels, to a point. The test in CA mentioned above protected themselves from dealing with this issue by adding the 87 gas while there was still other gas in the tank, then running the tank empty before filling up with 87 for the experiment. This gave the engine time to adapt.
If you’re driving an older GTI, it might not have that technology and you should definitely always stick to premium gas. If it’s newer, you should be okay going to 87 sometimes, but be careful.
Simply put, fuels with 91 octane and higher are recommended for cars with engines like the VW GTIs. Engines designed for premium fuel should be given premium fuel, and regular fuel should be given to regular engines. Any crossover could cause problems. (Source)
When in doubt, go to your Owner’s Manual. The 2015 VW GTI Manual says to follow the recommendation on the inside of the fuel filler. If it says to use premium gas, then use premium gas. However, the 2019 VW GTI typically uses regular gas. (Source)
Your car was designed to run on a specific kind of gas, and though it can adapt, it’s best to use the gas that’s best for it in order to ensure a longer life for your car and prevent engine damage.
Along with being better for your car, using premium gas is also better for you in case you need to use your warranty: using regular gas where premium gas is recommended could potentially void your warranty, or possibly even your insurance, should using the wrong gas be the cause of a crash or other damage.
You may have noticed that I keep using the word “recommended” and its relatives. That’s because it’s simply the right word to use. Unless your Owner’s Manual says that premium gas is “required,” then it’s “recommended for best performance.” If your manual says premium gas is “required,” that’s the end of the story: use premium gas. But “recommended” is a softer word.
That means that if your manual says “recommended,” you have options. That doesn’t mean you can change the gas you use on a whim: all of the above still applies. What it does mean is that you can use lower octane fuel, but it will reduce some of your vehicle’s performance.
Part of that is gas mileage: 87 octane gas will give your GTI worse mileage. The other part is knocking prevention.
If your GTI has a knock sensor, it will be able to detect a potential problem in the fuel and act to prevent engine knocking from happening. This function does cost your performance, though, as it takes power from the engine for it to work. That’s why premium gas is only recommended instead of strictly required.
You can try running your GTI on regular gas, and see if you can tell the difference in performance. All the same, unless you already know the difference (in which case you wouldn’t have read this) it’s still the best practice to fill your GTI up with premium gas to keep up the engine’s health in the long run.