Do you really need to put premium gas in a rental car? – Jalopnik

It’s common knowledge that buying a former rental car can be a way to score big on your next car. However, keep in mind that rental cars often have more imperfections than normal, such as extra scratches, dents and crushed wheels. After all, renters are unlikely to treat their temporary ride as carefully as they would a personal vehicle. And we haven’t even mentioned the tough driving techniques to which borrowed cars are sometimes subject.

We know Jalopnik readers would never abuse a rental car, but what about covering the extra costs if your next rental car requires premium fuel? On average, premium gasoline costs about $0.80 more per gallon than regular gasoline, which can really add up if you fill about 20 gallons. What we can tell you for sure is that not all cars need high-quality fuel. In fact, the majority are fine using regular gasoline, which has an octane rating of 87 or even 85 octane in some high altitude areas.

Unless premium fuel is clearly identified with a label or sticker on or near the gas cap of your rental car, don’t even think about filling up with regular gas. That said, even if your rental car calls for premium fuel in an obvious way, it still won’t hurt to use regularly, although it will hinder performance.

Powerful engines with high compression ratios or forced induction such as a turbocharger often require high-quality fuel. However, with the advent of computer-controlled engines decades ago, such cars and trucks can adapt to lower octane fuels if necessary. If you rent a Corvette that clearly demands premium, and you fill it with regular gasoline, the pistons won’t hole due to detonation or pre-ignition like they used to. Instead, the ECU uses knock sensors and other inputs to at least retard ignition timing. More advanced systems can also adjust valve timing or limit the amount of turbo boost to prevent engine damage when using lower octane fuel.

Such detuning of the engine to adapt to a lower octane number will obviously adversely affect performance and possibly fuel economy. If you’re just cruising around town under normal circumstances, you might not even notice the horsepower handicap of running on regular gas when premium is recommended. That said, the performance drop will be noticeable as you push the limits. For example, Mazda rates its 2022 CX-5 with a 2.5-liter turbo engine at 256 hp and using premium 93-octane gasoline. But that same engine, running on regular 87-octane gasoline, produces only 227 hp.

If your next rental car is designed for premium use, and you fill it up regularly during your rental period to save some money at the expense of optimal performance, that’s your prerogative. But at the end of the rental period, you may need to refill the tank at a gas station near the airport so you don’t have to pay high fees for returning the car with less than a full tank. That’s where the real moral dilemma begins.

Will you take into account the fuel cap’s recommendation for an octane rating of 91 or even 93 so that the next renter can enjoy the car’s full performance capabilities? Or say, fuck it, I’ll save some money on that last fill-up, even if it means the ECU will detune the engine for the next renter? That’s between you and your conscience, but just know that you won’t actually damage the vehicle or get picked up by the car rental police, like they do with those gigantic error-prone AI damage scanners.

Finally, it cannot be stressed enough that if your car, rental or otherwise, does not specify premium fuel (or even mid-range), just use regular fuel. With a few exceptions, like Ford’s EcoBoost range, anything else is probably a waste of money.