I know Lexus recommends premium fuel for my NX 300 AWD. I have talked to other users who say they always just use 87 octane. I tried 3 tanks of both and could not see any difference in performance (based on the conservative way I drive). I also did not find much difference in the MPG. Doe anyone else have more information on any adverse effects of the lower octane?

 

Lexus requires premium fuel, not recommends it. This is huge difference between two. If car manual states 93 (or 91) recommended, you can use lower octane gas without issues, unless you drive at high elevation (thin air). If car manual states that 91 octane gas is required, then it is required. Do not try to cut short as you risk damaging engine.
Incidentally, this topic has been beaten to death, so do search on this forum.

 

I understand your thinking on the matter. It’s hard to believe that a Toyota engine needs 91 octane vs 87. I’ve used premium but hate paying higher prices. 1.99 vs 2.99

 

Driven vehicles that required or recommended premium for over 750,000 miles with zero engine problems. As you stated I also experimented with premium have noticed no difference in mpg or acceleration.

https://www.cartalk.com/content/premium-vs-regular-1#4

 

Most of the time, the driver will not be able to tell much difference between 87 and 91 octane but that's does not mean that there isn't any. With turbo charge engines and its force air induction, it is even more important to use the right octane. Some turbo charge engines are design for 87 octane but the NX300 is not one of them. When you put in 87 octane in the NX, the engine's knock sensor will detect the engine knock and retarding the engine's timing to eliminate the knock. Since our cars are design for 91 octane, the engine will eventually try to advance the timing until it detects the knock again, in which time, it will retard timing again. Now imagine this happening over and over thru out the lifetime of your engine, the knocking will cause an incomplete combustion cycle timing and eventually cause carbon build up in the intake valves and engine sludge.

 

Hedge your bet and use 89 octane or fill with 93 and at 1/2 tank fill with 89 ,giving you 91.

 

Not to mention, if you were to ever claim engine damage and you're still under dealer warranty (I'm not sure if the aftermarket warranty companies do), they will most likely take an oil and fuel sample for analysis. So it's better to save yourself the headache and spend the extra couple bucks and use 91 octane.

 

Gas is cheap... seriously. The manufacture tells you EXACTLY what fuel octane to use. Sometimes there is a problem and you can't get 93 in an area or an emergency. I'm sure they have planned for this. But why would one want to run a lower octane than what the manual/gas caps tells you to put in? If you don't want to use the right octane then you shouldn't buy a vehicle that requires it. This isn't a rant on you the OP, but I'm not sure why we have so many threads on fuel octane. 95% of the time you will not notice it at all, but why take the chance on detonation or knock..etc. Sometimes premium vehicles require premium things.
And between 87 to 93 you are talking like a 10-15 dollar difference... That's like two star bucks coffees or put in something that you like to get that you'd skip twice in order to make up the difference.

-Nigel

 

I always wondered about this. If you fill half a tank with 93 and half a tank with 89, will that truly give you 91 ?
Let's assume for a moment that the fluids are well mixed.
There seems to be a big difference in price when going up from 89 octane (here in the northeast). Going from 91 to 93 is a small jump up.

 

in mathematics yes, (0.5 x 89) + (0.5 x 93) = 91

 

It is a high compression turbo engine and must use at least 91 octane. We had a customer come in with a P137800 Pre-ignition engine fault code in his NX after using 87 octane.

 

It's only about 60 cents more per gallon for "premium" over regular in my area. Our grades are typically 87, 89, 91 (some stations have 93 as the premium). So if your dead on empty you're looking at an extra $9 to fill up. Since most people have a few gallons left when they fill up we're probably talking about $7-$8. If you fill up once a week you're looking from $28-$32 a month.

 

Does it really cost the oil companies 60 cents more to manufacture 93 octane compared to 89 octane? I recall mid-grade being 10 cents more than regular, and "supreme" 20 cents more than regular. Is there a way to add octane increaser to 89 octane gas to make it run like a 93 octane, but for less than 60 cents per gallon?

 

No, it doesn't cost that much. Oil companies have seen the demographics and they know cars that require premium are often driven by people who can afford 60 cents more a gallon.

You could use an additive like this:

https://www.amsoil.com/p/dominator-o...IaAiv6EALw_wcB

Of course, it's $10 a bottle...one bottle per tank.

 

Here is an interesting article regarding a Lexus rep and premium fuel.

https://www.google.com/amp/s/blog.co...?client=safari

According to Doug Herbert at Lexus, “Required” is a bit overstated:

Herbert said that both vehicles (an RC 350 sports coupe and an NX 200t compact SUV) will run on regular-grade fuel without damage. But since both the advertised power ratings and the EPA fuel-economy figures were attained using premium, that’s what they have to put as the required fuel. However, he also warned that continued use of regular-grade gas would cause the engine’s computer to back off on the ignition timing—thus adversely affecting both power and fuel economy—and that it would continue to do so for a time even after the car is filled with premium.