89 Or 93 Octane Gas For Lexus Rx300 - What Is Everyone Using

[FloridaRX]

I'm switching out my o2 A/F ratio sensors, and fuel filter since they need to be changed. However, I'm thinking of switching gas frm 93 to 89. I don't drive my RX a lot during the week. On the weekends, it's a little more.

Can I get a few opinions on what everyone is putting in their gas tanks and if you will change to a lesser octane gas?

Thanks for reading!

[lenore]

here in california I use 91 octane. I question why change fuel filter....It is inside the fuel tank and generally from what I have heard and read on these sites should never need replacement unless someone has contaminated your fuel tank. Also please note: the Air fuel sensors should only be replaced with Original equipment ones as the Bosch ones are not generally happy in these engines. Make sure it is a Denso air fuel sensor.

[FloridaRX]

I didn't purchase my RX from a Lexus Dealership. I pulled the carfax report and I'm missing two years of vehicle maintenance on my truck. I've gotten several trouble shooting codes which gets me thinking the truck was not properly taken care of. I'm getting crappy gas mileage. Maybe 50 miles for a 1/2 tank of gas. So I figured I better change the fuel filter as well. Thanks for your insight.

[smooth1]

These vehicles have a "learning" mode that establishes some settings over time based on the drivers habits. You may need to "reset the ECU" so it will go back into the learning modes with you as the new driver. There is a seperate proceedure for clearing out the transmission memory as well.

I agree with lenore in that you don't have to replace the fuel filter unless you have particulate contamination in your fuel tank like chunks of rust or dirt and so on. You may want to look before wasting time and money.

If the vehicle specifies 93 octane, you might want to reconsider going to 89. That's more of a jump than lenore going to 91. Understand that the octane ratings are not "quality" ratings. They are a measure of resistance to ignition. 89 octane has less resistance to being ignited than 93 octane. Because of this, as the fuel is entering the cylinder, you will be more prone to pre-ignition, or spark knock than if you were to use 93. Which will mean less horsepower, (fuel is igniting before piston reaches top dead center), and rougher idles and lower mpg's. All that can add up to more money than if you were to just use the right octane. Can you get away with a lower octane? Probably. Will it damage your engine? Possibly. Given the used status of your purchase, the mileage and year, missing some maintenance, I would just stay with 93 for at least the first year of ownership. Get to know your new vehicle first. Then if you put in 89 and the change ok with you, then you at least know what's going on. But I'm puzzled at the fact that the fuel filter and maintenance history bother you, yet chincing out on the fuel is ok ?

[LEX-SV]

In northern California, premium gasoline averages about 5% more in cost or an extra 20cent per gallon over regular. In other words it's really not that big of a cost difference, so if the manufacturer of my particular car specficies premium, that's what I use.