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Regular gas vs Premium

I’m interested in buying an '09 Infiniti FX35 rearwheel drive. If is recommended to use Premium gas but the salesman said he has seen info indicating that Regular is OK but will lose about 5% of power without damaging the car. Does this make any sense to anyone?

What he said makes sense, but first make sure the term "recommended" is used by the manufacturer in the owner's manual.  Also remember that in addition to the loss of power there will also be a loose of mileage, meaning it could even cost you more to use regular. 

Repeat after me:

High Octane gas does not help an engine that does not need it. Octane is not a measure of quality or power.

Octane is a measure of how easy the gas starts to burn or how fast. High octane means it is hard to start burning. On the other end diesel is measured by certane and a high certane number means it is easier to start burning.

High octane gas may or may not have more additives like cleaners in it, but with today’s regulations any gas has enough for most engines.

   The owner's manual will say that it must have high octane or that it may use regular but should use high octane.  The parts the leave out are:

  * If it needs high octane, using regular can damage the engine.

  * If it should use high octane then it has a system to sense the low octane and to make adjustments to the car that will protect the engine.  However the adjustments will result in lower mileage (reducing or wiping out any economic advantage) and will reduce the power, defeating the reason most people buy cars that require high octane. 

  * Using high octane in a car that does not recommend it very very seldom causes damage but cost you more and offer no advantage.

Car salesmen/saleswomen are extremely poor sources for accurate information regarding the cars that they sell.
If you want accurate information on this issue (or virtually anything else regarding the safe and economical operation of a car), you have to read what is stated in the Owner’s Manual.

I have heard statements from car salespeople that are so bizarre, one has to wonder if they know anything about cars in general (beyond any specific knowledge of the cars that they sell), or even if they are aware of other bits of knowledge that any adult should know. Perhaps the most bizarre was a salesman’s explanation of how the Traction Control system works. He stated that when the TC button on the dashboard is pushed, “it makes the car heavier”. I replied that I was extremely impressed that the car’s manufacturer was able to repeal the laws of physics, and then I exited the showroom in search of intelligent life.

Read the Owner’s Manual!

put the best fuel in your new car!!especially because your petrol is so cheap!!!try living in england where i pay the equivalent of $10 a gallon!i always use a name brand like shell,b.p,etc.because they put additives in the fuel to keep your engine clean,and i use the highest octane which is 97 in the uk.some people over here use cheaper supermarket fuel,but why bother ? ?because you only save about a pound per tankfull,id sooner have the best.

don’t about yours but i filled up w/reg by misstake in my 92 jag. had to drive it out.didn’t see any diff. then tried in my 88 xjs v-12 same thing. no valve rattle, still run up to 140 if i want to.still get 26 on the open road. going to try in my 2000 cad next. so far only diff has been in wallet.

I’ve found in many cars that can benefit from premium fuel that the increased cost of the gas is mostly offset by slightly improved gas mileage. The results very, but I prefer the way a car runs that can take advantage of the increased ignition timing that premium allows anyway.

Thats about as completely wrong as can be in the USA.

Here gasoline is delivered to depots via pipeline. All brands in the region buy gasoline out of the same pipe. The only difference is when the delivery truck is loaded they break open a pouch of the desired brand’s additives. Ethanol is optionally added at the same time.

The EPA mandates a strong dose of additives to keep injectors and intake valves clean. Some try to claim their brand does better than others, but there is very little evidence to support such statements.

As for the vehicle manufacturer’s recommendation one must read the manufacturer’s statement very carefully. I had a 2000 Avalon where the official statement was crafted so as to tell those who want to buy premium gas to go right ahead, yet said “87 octane” to anyone used to reading data sheets.

Some people (many Avalon customers) want to be told they have to buy the most expensive goodies for their car.

I have been running regular in my 2004 FX35 (all wheel drive) for about four years… “Premium recommended” means that they used premium to get the performance and horsepower numbers, but the engine will dial itself back if/when you use regular. Some require premium… don’t put regular in them. …I don’t know if the 2009 ‘recommends’ or ‘requires’ premium, but my 2004 ‘recommends’ it…