Tip & How-To about Toyota Prius

Why to Use a fuel with the lowest required octane in the car?

Low-octane "regular" gas is usually all that is required. Octane is only a rating of the fuel's resistance to engine-damaging pre-ignition ("knock") in high-performance engines (that few people have). Low octane gas is less expensive and a better value if that's all your engine requires. Best case scenario you're wasting money by filling up with a higher than recommended grade of gas. Worst case scenario that high octane fuel is building up damaging carbon deposits in your engine because it's not being burned as completely as lower octane fuel would be. Check your owner's manual to be sure. Modern high performance cars will sometimes recommend higher octane fuels because they are engineered to use those fuels. The use of lower than recommended octane will not make your car explode, the ECM (Engine Control Module, aka:computer) will adjust the fuel injectors and spark timing to save the engine and compensate for you cheaping out at the pump. Those adjustments will consist of retarding the spark (reducing power and efficiency) as well as dumping lots of extra fuel into the cylinders to cool them, potentially costing you more than getting mid grade or premium IF that's what your car requires. NOTE: Remember that engines need less octane at higher altitudes. If your engine does not "knock" on regular, paying more for a higher octane rating is a waste since the increased octane makes no significant improvement to gas mileage and it is no better for your engine. All available fuels have detergent and additive packages. This will help.good luck.

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2 Answers

Can I use 88octane-15% ethanol in my 2011 ram hemi


The owners manual probably says no. Most say 89 octane is the lowest. Look in manual if you have one or they are typically on-line. With that said, test your vehicle with that fuel. Next time it is very close to empty put 2-3 gallons in the tank and drive. If the octane is too low the engine will "spark knock" or "diesel" (a rattling sound from the engine upon acceleration caused by fuel pre-ignition/detonation). If that happens put an equal amount of premium fuel in the tank and the spark knock will go away. Short-term a spark knock won't damage an engine, but longer term can by causing over heating, vibrations, abnormal stresses ... hesitation on acceleration - poor mileage and poor engine performance. If you are able to use 88 octane-15%, without getting a spark knock, make sure you check your mileage and see if, or how much, it drops. Lower octane and higher ethanol both reduce mileage. What I always told my gas customers was to check your mileage with different octanes and see what octane gives the highest mileage (and then do the math and see if its cost effective). Say you use regular normally and you get 30 MPG. Then you try the mid-grade and get 33 MPG, so you try premium fuel but you still get 33 MPG. In that case the mid-grade is your best option, assuming that your 10% increase in mileage cost you less than a 10% increase in cost! But you do always stay away from fuel that causes a spark knock.
The rule of thumb is: The higher the octane the cooler the combustion, therefore the lower the octane the hotter the combustion. Higher ethanol means that the engine is running a little leaner and a little hotter.

Mar 09, 2018 | Cars & Trucks

1 Answer

Is Premium and higher octane better than regular gas in Mazda 3, 2012 car?


Octane ratings have nothing to do with fuel economy or power. The octane rating only indicates how much the fuel air mixture can be compressed before it ignites without the spark plug firing in a hot running engine. Some really high compression engines require higher octane fuels so they don't knock when running. If you don't have a sticker under the filler lid that says you have to use one of higher octane fuels, then don't use high-test.
It used to be that using a low octane fuel in an engine designed to use high octane fuels could damage the engine.
Nowadays, engines are all computer controlled and most high octane engines will re-tune themselves on the fly so that they don't knock if the wrong grade of fuel is used.

Feb 20, 2015 | Mazda MAZDA3 Cars & Trucks

3 Answers

what is the cause of detonation noise ?


Wrong spark plugs?
Make sure you use iridium plugs by NGK or Denso.
NGK V-Power Plugs BKR5E-11

Carbon Buildup?
Get some Techron and run several tanks

Wrong Octane?
Your engine should use regular gas. But you might be getting some low grade gas. You can try using a higher octane fuel. Or try adding a octane booster.

Jul 21, 2014 | 1995 Mitsubishi Montero

1 Answer

What kind of gas does a maxima 2001


According to page 10-3 of the 2001 Nissan Maxima Owner's Manual:

FUEL RECOMMENDATION
Unleaded premium gasoline with an octane
rating of at least 91 AKI (Anti-Knock Index)
number (Research octane number 96)
If unleaded premium gasoline is not available,
unleaded regular gasoline with an
octane rating of at least 87 AKI (Research
octane number 91) can be used.
However, for maximum vehicle performance,
the use of unleaded premium gasoline
is recommended.

Engine "knock" is not just an unusual sound - but over time can cause real damage to the engine. You *should* use fuels with the recommended octane levels, but if you choose to use fuel with a lower octane level due to reduce fuel costs - do not repeatedly use fuel that causes engine knock. Find the "sweet spot" between the cost of lower octane fuel and an octane level that does not cause knocking. Expect fuel economy and performance to drop with lower octane fuels, too.

Good luck!

Feb 12, 2012 | 2001 Nissan Maxima

2 Answers

What part of the engine knocks when your knock sensor is bad on a 11995 cutlass supreme sl


Hello: The Knock Sensors purpose is to detect pre-ignition, when the computer receives a knock signal it re tarts the timing to prevent the pre-ignition. Any mechanical related knock will activate the knock sensor signal. If the knock sensor is bad it WILL NOT cause the engine to knock.......

Sep 15, 2011 | 1994 Oldsmobile Cutlass

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