Sorry, If I'm late into this discussion.. but OP had an '13 RX350 (Which uses Regular), and he wants to buy or did buy a NX200t (which uses Premium) according to MPG.GOV.

The NX only gets 3 mpg better hwy and 4 mpg better city but need Prem Gas.. The Difference is Negligible.. i mean Annual fuel cost based on MPG.GOV is only $50 less a year going with the NX.. https://www.fueleconomy.gov/feg/Find...32343&id=35912

I mean If I were in this situation.. Just Keep the RX350.. and with all due respect to the OP.. But I don't understand how people get themselves into this frame of mind..BUT (I've been there too trying to save here and there but most times you end up spending more by saving the wrong way) ie.. Also using Regular 87 gas in a higher compression engine that requires higher-octane.. You end up burning more fuel in the NX using 87 so the gas mpg will probably ended getting the same as the RX350 and the NX will run crappy and risk internal damage.. Big win for OP.. Anyways, people will do anything to save a buck.. but will spend alot more in the long run..

Sorry, if it offended the OP, but I'm justing stating Facts.. (Trying to be helpful here)

 

Fuel economy gains can depend on one’s personal situation. My previous 2011 RX350 was spec’d to run on premium, but it ran on regular. In doing so, however, one sacrificed some performance and mileage. Because of this, I tended to use some grade above regular (87octane). The best that my RX would usually otain on the highway was 24 mpg and 18 mpg. in town.

My new NX200t appears to be getting an average of 22 mpg in town and nearly 29-30 mpg on the highway (it is relatively flat here). That is ~ 25% improvement in overall gas mileage over what I obtained with my previous RX. Our local BP station sells 93 octane gasoline at a $0.20/gal. premium and at a $0.10/gal. premium for 89 octane gasoline over 87 octane fuel. One could mix 89 and 93 octane from time to time to realize an extra cost of ~ $0.15/gal. Assuming a $2.50/gal base price (about on the money here these days), this represents something like a 6 – 8% increase in the price of fuel costs over the use of regular 87 octane. This figures out at a roughly ~18% savings in total fuel costs using the new NX in my circumstances (keeping in mind that in reality I usually used something better than 87 octane in my RX anyway).

This represents a modest savings to be sure, but still a notable one. For those for whom it matters, the carbon footprint is smaller with the NX … and it more fun to drive than the RX, too.

Need I say, YMMV.

 

If you would have click on this previously posted link, I compared OP's old car to his new car, is what I was talking about.. https://www.fueleconomy.gov/feg/Find...32343&id=35912

 

See, and this is where the issue is. When you car says to run premium, its not an option for you to be scrooge and put regular in it. I am not overly sure WHY people even debate this. The car is told to run premium due to compression ratio and timing.

To this day it stuns me, I figured I'd hear this type of cutting corners conversation on a Ford forum, but you bought a Lexus, and want save a dollar...

 

You'd be surprised how often this question is asked in the other premium brand forums.

 

 

Yeah, I'll +1 that as well.

 

Because it was shown that some manufacturers actually inflated the fuel requirements as a marketing tactic rather than technical requirements. The premise that people associate a premium car to NEED premium gas, rather than regular gas, and oil companies are marketing premium gas as such too.

On an energy basis, there is no difference between regular and premium. The both contain the same amount of joules when burning. It's how the engine management system handles compression and ignition timing that makes the difference as which gas give more or less mpg. The difference in octane level is all about knock prevention (that can and should really be a function of engine management, not gasoline requirement) and additional detergents that are not mandated by the DOT. Those additional detergents are not and should not be required by the engine manufacturers, as they design the engine based on the most common denominator which is DOT requirements.

Regardless of how much I make, or how much I paid for my car, I would always opt to keep some money in my pocket, rather than the oil company's pockets. If the car really needs premium due to technical requirements (knock prevention) then yes, use that. If not, then, sorry, no need to use that.

Here in Canada (specifically Ontario) most stations have a $0.20/litre difference between regular (87 octane) and premium (91 octane). That's a 76 cents a gallon difference. This means that I can pick up a full tank and lunch using regular or just a full tank using premium. Hmmm.

 

I feel luxury auto manufacturers would love to have a 87 octane recommendation.
Lexus dropped the premium to reg with the ES and RX with no changes to the 3.5L.
Don't you think Lexus would love to have a 87 recommendation for the NX?It's premium for a reason.

 

We most of the time agree on things, but this is going to have to be a agree to disagree. I don't believe in the whole "they are out to get us". I've looked at the tuning of WAY too many cars to see the reason that you have a specific fuel requirement. Heck, look at the 2013 GT-R, it is tuned for 93 from the factory, and if you don't use it, the car will lose boost and under heavy load go into limp mode. My Camaro from the factory required minimum 91, if you didn't use 91, the car would knock in the cold (not mine, but reviews from the forums).

I understand the 76 centers per gallon sucks, I would complain as well. However, I wouldn't risk the motor in my car over it.

 

Yes there as been much debate over the years between Regular Octane VS Premium octane.

Average cars have a compression ratios that can use regular octane gasoline.
Premium car with high-performance engines have higher ratios. They require high octane gasoline.

If you have a premium car the requires high octane gasoline, spend the extra cash at the pump and get high octane gas. The high cost of buying a higher performance car also comes with a higher cost of owning it. If cost of gas is that much of an issue.. then trade-in/buy something else.

 

I think we already agree. If you read my statement, I am clear that if there is a technical reason to require premium, then so be it. That happens in high performance / high compression ratio engines. But it should not be solely because "it's a premium car so it should use premium fuel", that is marketing BS. It should be because the technical requirements justify it. That's the engineer in me, not the "hey I bought a Lexus, so I am going to **** my money away in my tank so it can burn at each stroke of the piston" talking.

Heck, I think most small 4 bangers in entry level cars should require premium as they are being squeezed too hard, but they don't because they do engine and ignition management so well.

BTW, they are not "out to get us", they ie (marketing folks) have a vested interest to maintain the perception of "premium" for a particular product and premium gas does that. The oil companies have a vested interest to ensure they maintain healthy margins. If they are going to have to keep 2 grades of fuel, then might as well differentiate it (detergents and additives) well and boost the price too. As a consumer, we have to be smart on what is "needed" versus what will make us "feel good".

For the record, I use premium if the manual calls for "premium required", I use a premium or regular on a rotation basis (2 fills regular, premium) or mid grade if the manual calls for "premium recommended" and I use regular if the manual states so. You will know the marketing BS when you read the "premium recommended" part. That is the marketing department 's compromise because the engineers didn't agree that premium was "required" and the lawyers provided the middle ground statement.

Specifically for the NX, I have gone of record stating that premium is the best choice:

 

I have always had the opinion that you should live within your means. Whether it is your car, your house, vacation or your get-a-way in cottage country, you shouldn't invest if it will have a significant impact to your quality of life.

Spending money frivolously is one thing but trying to save money by ignoring mechanical requirements is irresponsible.

I can understand someone debating the issue if they are otherwise unaware of the mechanical differences between regular and premium fuel requirements, however, on this forum there is more than enough information to fill that void.

Premium fuel "recommended" I can see being a trickier debate since it does not otherwise state required.

 

Gas prices have and continues to crater. Not sure why anyone would want to mess around with fuel types.

 

I suppose you can do that if you are under the impression that you are smarter than the engine designers who required you to run premium...[/QUOTE]

300 H does not require premium, it's 87 and above. Smart enough to read the requirement of my car.