Regular Grade Gas and its Effects on Car Engines

[moriah]

TL;DR Summary

I remember when I was in high school, most of my friends and acquaintances would claim that regular unleaded is bad for a car’s engine. Is there any truth to this?

Is regular grade gas detrimental to a car’s engine?

 

[Baluncore]

It depends on the compression ratio of the engine and on the octane rating of the fuel.

It did depend on the cylinder head valve seat materials, which changed when lead was removed from gasoline. Older engines could be damaged by unleaded fuel, newer ones are not damaged.

 

[anorlunda]

Tetraethyllead in fuel helped prevent valve wear and knocking. When lead was cut back, there were lead substitute fuel additives you could buy (they are probably still available today.)

https://en.wikipedia.org/wiki/Tetraethyllead

But the manufacturers also adjusted the design and the materials of the engines to compensate for the lack of lead. For example, ethanol raises the octane level without lead. Also, "[they]began specifying hardened valve seats and upgraded exhaust valve materials to prevent valve recession without lead."

The Wikipedia article also exposes the real reason for use of lead in the first place.

TEL offered the business advantage of being commercially profitable because its use for this purpose could be patented.

See https://en.wikipedia.org/wiki/Ethyl_Corporation for more on that.

So what you learned in high school may be obsolete today. If you attended high school as many years centuries decades ago as I did, nearly everything is obsolete.

 

[russ_watters]

Is regular grade gas detrimental to a car’s engine?

Define "detrimental" and "grade". Assuming you mean octane rating: The purpose of higher octane gas is to eliminate pre-ignition/knocking at higher compression ratios. So if your engine doesn't have a high compression ratio, there's no benefit to higher octane gas/detriment to lower octane.

Engine knocking can damage an engine. So if you do use low octane gas on a high compression ratio older car, yes, it can be detrimental. But newer engines with computer-controlled timing and combustion have knock sensors that can make adjustments in ignition to avoid the knocking and reduce the potential for damage:
https://www.thedrive.com/cars-101/35148/what-is-a-knock-sensor

The bottom-line is: Read the car's manual (or look on/in the gas cap) to determine what kind of gas to use.

The below-the-bottom-line is: My car (Kia Stinger, 2.0T) has vague guidance that has been altered between model years to be even more vague. Higher octane gas is recommended but evidently not required. There's spirited debate online regarding what this means, with the consensus seeming to be that if you use lower octane gas against the recommendation, the likely result is going to be slightly lower fuel economy but no harm.

 

[moriah]

Tetraethyllead in fuel helped prevent valve wear and knocking. When lead was cut back, there were lead substitute fuel additives you could buy (they are probably still available today.)

https://en.wikipedia.org/wiki/Tetraethyllead

But the manufacturers also adjusted the design and the materials of the engines to compensate for the lack of lead. For example, ethanol raises the octane level without lead. Also, "[they]began specifying hardened valve seats and upgraded exhaust valve materials to prevent valve recession without lead."

The Wikipedia article also exposes the real reason for use of lead in the first place.

See https://en.wikipedia.org/wiki/Ethyl_Corporation for more on that.

So what you learned in high school may be obsolete today. If you attended high school as many years centuries decades ago as I did, nearly everything is obsolete.

Technology has improved our lives in ways that a layperson like me, wouldn’t even know without forums like this one. It’s also destroying our lives, but that’s a whole other show.

 

[moriah]

Define "detrimental" and "grade". Assuming you mean octane rating: The purpose of higher octane gas is to eliminate pre-ignition/knocking at higher compression ratios. So if your engine doesn't have a high compression ratio, there's no benefit to higher octane gas/detriment to lower octane.

Engine knocking can damage an engine. So if you do use low octane gas on a high compression ratio older car, yes, it can be detrimental. But newer engines with computer-controlled timing and combustion have knock sensors that can make adjustments in ignition to avoid the knocking and reduce the potential for damage:
https://www.thedrive.com/cars-101/35148/what-is-a-knock-sensor

The bottom-line is: Read the car's manual (or look on/in the gas cap) to determine what kind of gas to use.

The below-the-bottom-line is: My car (Kia Stinger, 2.0T) has vague guidance that has been altered between model years to be even more vague. Higher octane gas is recommended but evidently not required. There's spirited debate online regarding what this means, with the consensus seeming to be that if you use lower octane gas against the recommendation, the likely result is going to be slightly lower fuel economy but no harm.

I did a little online research. What I’ve gleaned is that unless you drive a high performance car, like a sports car for example, and unless the manual specifically recommends it, spending money on high octane gas is pointless.

 

[cjl]

That's basically correct. Even though as Russ said, there are mechanisms where modern engines will try to prevent damage from a too-low octane, you absolutely can still destroy a modern engine (or at least some modern engines) if fuel with insufficient octane is used. However, there's no benefit to using octane higher than what the engine requires.

If you drive a car where the manual or the inside of the fuel filler cap states "premium fuel only" or has a specified minimum octane, you should absolutely follow that, but there's no benefit going further above what the engine requires. As you said, nearly all cars that require higher than regular grade gas are sports or high performance cars, so unless you drive one of those, you almost definitely gain no benefit by going to premium above regular (but check your manual if you want to be sure).

Some people believe that higher octane makes more power, but that's not true. High power engines use higher octane, but that's because they are actually unable to run safely on low octane. Running a higher octane would allow you to modify your engine for more power, but just switching to a high octane will not change your engine's power output in any measurable way.