My car says "premium unleaded only" What harm could it do to use regular unleaded?

Question

I appreciate the replies, but "ruin the engine", "damage the engine", etc. doesn't say anything about what harm it could do.

It's a 2003 Infiniti Q45 that I've had since new. I have all the paperwork, manual, etc. and have been using Premium fuel.

Answer 1

Higher octane gasoline resists ignition under higher pressure and heat. The octane rating is thus a measure of resistance to preignition (knock). Preignition means that the fuel/air mixture ignites before it is supposed to.

Visualize the piston coming up in the compression stroke with a cylinder-full of explosive fuel and air, and imagine the effect if that mixture exploded before the piston reaches the top of its stroke. Instead of pushing down on the piston to drive the crank and make power the way it is meant to, the explosion is pushing against the rotation of the crank.

Something has to give. Usually it's the piston or the piston rod. Very dangerous and very expensive.

Your Q has an acoustical 'knock sensor' that listens to the engine and retards the spark if 'incipient knock' is detected.

This is a safety factor so that if you find yourself in a situation where high octane gasoline is not available, the spark occurs later in the combustion cycle (when the piston has started its downstroke), where compression is lower.

This does nothing to reduce the peak compression, but the later spark also reduces the heat build-up in the cylinders enough to prevent preignition.

Your car does have such a system, so the only short term negative result of using lower octane gas is a reduction in performance, because the force of the explosion is now driving the piston over a lesser portion of the stroke, and the effective compression is lower.

However, there is also the possibility that if you continue to use a fuel with lower octane than recommended by the manufacturer, and there is damage due to preignition, you may have voided the warranty.

If you were to use low octane gas say, while climbing out of Death Valley with the ambient temperature around 115, I wouldn't count on the knock sensor to protect the engine.

Answer 2

Many cars have this sticker near the tank. Very few of them actually need to use the "Premium grade" gasoline that the sticker recommends.

You do not give particulars about your vehicle, and it's not likely you have the owners manual if it is a used car. So, lets assume you don't have the manual and figure it out. Have you actually tried to use the regular grade of gasoline? As some have noted if you need premium your car may ping on regular gas. But, usually on regular it will just run a bit rougher and extreme levels of performance will be affected. Engines in newer cars are typically more isolated (especially when the windows are down the air conditioner is on and the radio is playing) and rough idle is difficult to detect. Try putting 1/2 a tank of regular when it is down to 1/8th. Run it for about 8-10 miles (so you know it's running on the regular gas and not the premium in the gas lines) park it (somewhere safe of course, like your driveway) and open the hood. Observe. If the car is running smoothly, it doesn't need premium.

Manufacturers put these "premium " stickers on the cars so you put in expensive gas. Sometimes this expensive gas is a bit cleaner and has more detergents to keep the engine cleaner (this is not guaranteed just because it says premium). How can it hurt the manufacturer anyway? They don't pay for the gas! And there is a slight chance (extremely slight) it may help the engine run with fewer problems during the warranty period!

Check it out. Then use regular if you can!

Check the manual. It should tell you what octane rating the engine needs to run properly. If it does not make a preference try what I recommend with the regular gas. And if it NEEDS premium the owners manual will say so!

Answer 3

It calls from the premium unleaded because it's a high compression engine. Using regular could lead to a degrading of performance, and pinging, which in time would ruin the engine. So it the $6 or so extra per fill up is killing you, sell it to someone who will appreciate it and buy yourself something that calls for 87 octane instead.

Answer 4

Its a high compression engine, high compression engines "crush" the fuel to air mixture more before the spark plug fires and ignites the gas but when they do this the extra compression causes more heat, higher octane gases dont ignite as easy and allow the high compression. If you engine is suppose to fire at bam------bam------bam------bam with high octane gas in it and you put low octane in a high compression engine it will fire out of sync or like
bam--bam-----bam-bam because the gas is igniting before the pistons reach the top of thier stroke. This will cause the individual pistions to fight themselves puttin excessive stress on your crankshaft and cams. Also the valves will wont be all the way open or closed which will cause harmful buildups on the valves as well as a loss of preformance because the valve will be letting pressure out that is supposed to be traped to harness the energy and drive the car, think of it as if you drilled a hole in the side of a firecracker and lit it. It still might explode but it wont be as loud as it should be.

The effects of the low octane gas wont be immediate but it will really make your engine crappy a couple thousand miles down the road.

Answer 5

Using too low of an octane rating will cause detonation or pre-ignition (usually causes "pinging" when accelerating, towing, or going up hills) which in the long term will burn pistons and valves. The heat causes the alloy in the pistons to crystalize. eventually the ring lands will crack on the pistons, or holes will burn in the tops of the pistons. It doesn't happen overnight, but it will definitely shorten the life of your vehicle.
It's possible to change the spark plug heat range to a lower number and slightly retard the timing to eliminate the detonation. But it's best to use the higher octane rating fuel.

Answer 6

Your car's engine was tuned to run more efficiently on Premium unleaded.....

You will not get as good MPG and the lifetime of your engine will be compromised

Answer 7

Very damaging to the engine over the long run. You will notice a lot of pinging when you push down on the pedal.

Answer 8

block up your injectors, put a carbon build up in the valves and make the engine slowly clog up really... but it wont happen overnight...... it'll take a while.. oh and ur car (if u have run it all the time on premium) will fell like its running like a busted ***....

Answer 9

Much. I would strongly recommend that you do not do that because if you put the regular gas in there, your car will say "Why the hell did you give me that stuff? I feel like crap!"

Answer 10

I agree with ty. Try using a lower octane and see if you hear any pinging noises. If not then you will be fine