Hi, I just got 2015 ILX. Like the car a lot. Book says to use premium gas, but dealer said can use regular. Has anyone measured efficiency (mpg) gained by using premium? Will it do any harm to use regular? Thanks.

 

what trim did you get? 2.0L or 2.4L?

 

I've heard you have to worry about knock on less than 91...
I would recommend you stick with what Acura suggests.

 

2.0 5 speed auto.

 

I would stick with what Acura suggested you run. Who ever suggested to you that you can run regular gas, i would ask if he has tried it and how the car runs

 

It looks like the 2.0 ILX has the R20A1 engine. I don't know anything about it, but Wiki says it has a 10.5:1 compression ratio. Compression ratio isn't always the end all say all when it comes to what kind of fuel is required, but a 10.5:1 isn't terribly high. I'd bet you could get away with regular or mid grade. But I'm with the others. I'd go with whatever Acura recommended.

I don't believe auto manufacturers always have your best interest in mind. But when it comes to fuel octane, I fail to believe that there's some sort of conspiracy between automakers and oil companies where a higher octane would be recommended when it's not needed. In fact, a car requiring higher octane fuel is usually seen as a negative attribute when purchasing a car. If they could engineer the motor to have the same power and performance with regular fuel, they'd do it since it would be a good feature to tout. That's the case with a lot of these direct injection turbocharged vehicles. It's considered a feature to sell a higher horsepower, efficient and turbocharged vehicle that only needs regular. Unfortunately, with standard port injection - most engines with compression ratios over 11:1 are going to need premium or they'll experience reduced performance and economy.

 

Then there are engines like the SkyActivG 2.5 in my wife's 2016 Mazda3 s GT; it is normally aspirated, has a compression ratio of something like 13.0:1, and runs on Regular 87 AKI fuel.

 

How long do you plan to keep the car? I like to stick with manufacturer specs, as I keep my cars for 15+ years. But if you know you're going to dump it in a few years (such as a lease) I would drive the hell out of it and do the least amount of maintenance possible.

 

Looks like there really isn't much of any difference between the R18 and R20 family of engines, specs look near identical between the older ILX's vs CR-Vs and Accords which also used them. Heck the R20's used in newer civics have a 10.6:1 comp ratio and run on standard gas. For your R20 engine in your auto ILX i wouldn't worry about it.

Now if you had the 2.4L 12-15 ILX which is basically a Si engine, or 16+ 2.4DI engine which is a higher performance varient of the current Accord engines... I would only use Premium on them as those engines are much more performance oriented and designed/optimized for 91+ fuel.

 

I agree, 100%. I'd at least test it out and see what happens.

 

There is a "knock sensor" that will adjust the timing should there be a difference in octane levels. The car computer will back off the timing if needed.

If you are more of a lead foot driver (especially high revving) then I would definitely recommend staying with Honda/Acura specs, however if not and based on the 2.0 L engine you could probably get away with it. I would recommend you trying it out first going from 91 to 89 octane first and see if there is an appreciable difference in driving performance and fuel economy, after that then you could try going down to 87.

Honda makes solid engines and the vehicle will not break down nor will it drive like sludge if you change the octane.

 

Regular.

 

I can give my experience with my 2013 2.4L. I started off using premium (91 octane in a higher-elevation area). Then after a few years I switched to regular (having moved, now 87 octane in a low-elevation area). I noticed a drop in fuel economy, but the drop in price was even bigger (2-3 MPG drop, but 50-60c/gal drop) so I was saving money. I think I noticed a slight performance drop, but it's hard to be certain.

However, as time went on, my car kept running worse and worse. The engine was louder and less smooth. After a year of that I switched back to premium (now 93 octane in the same low-elevation area) and the car is back to running smoothly and quieter (although, it's obviously not a quiet car in general). It's like brand new, again. So, for me, I like premium, even with the higher price tag. As I'm now down to about 4-5k miles driven per year, it doesn't make that big of a difference cost-wise, but gives me a better driving experience and considerable more confidence in my car's longevity--if the engine is gasping and straining some at regular octane levels, how much stress is that putting on things?