BertL

I personally agree with you, but as you've likely observed in numerous threads, there are many others that have their own views and take different action from that of the mfgr recommendation. To each their, and our, opinion -- and how that effects pocketbooks and possibly our rides.

kitlz

Yup, the poor dead horse can't rest in peace. Some people will use whatever octane gas they want regardless of the recommendation in the manual.

NateJG

When I sold my German car, the fellow that bought it asked whether or not I used the prescribed Premium fuel -- to which I replied by showing him all of the gasoline receipts for the car.

He told me that if I was that OCD about fuel - surely I was as diligent with maintenance as I had claimed.

He bought the car at a substantial premium over the Edmunds suggested price.

mtmendez

Thanks for the fact checking! I stand corrected! They are such nice vehicles I thought for sure there would be more on the road!

NateJG

Actually, I wish you had been correct - as it would mean my replacement battery (heaven forbid) wouldn't bankrupt me.

tempestv8

The octane number in the USA is a bit confusing for folks in other countries!

USA Octane 91 = Euro 95
USA Octane 87 = Euro 90

In Australia, in most petrol stations, in addition to straight unleaded (Euro 91, 95 & 98), one can also purchase unleaded petrol with 10% ethanol added to it, which gives it an Euro 95 rating. So the addition of the ethanol to standard unleaded fuel brings regular unleaded up to the equivalent of USA 91 octane, premium fuel.

On the fuel flap of the Lexus, there is a sticker attached which says E10 fuel is permitted. The best part about this fuel is that it is cheaper than the standard unleaded. Not so good is that this fuel does tend to be consumed at a higher rate due to the lower energy value in the ethanol, but it does increase the octane level, which is important just to reduce the chance of pinging under load. Is this the same as for North American spec vehicles?



Lexus Australia recommends Euro 95, which equates to USA 91 octane (RON+MON)/2, basically premium gasoline, in USA parlance.

As someone else on this thread alluded to = it's a pricey vehicle, so why cheap out by putting in lower grade fuel?

My thoughts:

1. Given the spark plugs are only replaced at the 100,000 mile interval, the higher octane fuels are probably going to help prevent the plugs from fouling sooner, compared to using cheaper fuel
2. Being tuned for economy rather than outright performance, the 2GR-FXE engine in the 450h will spend far more of it's time at the lower end of the rev range, where the engine would be more suceptible to pinging rather than the RX350 which will be revving higher due to its conventional gearbox. Using a higher octane fuel will mitigate the risk of sustaining long term damage caused by pinging.

Freds430

This is probably the most heated debate on these forums. Do whatever makes you comfortable. I use 87 octane in our 2015 RX450h. Experimenting with the other two levels, I have noticed zero difference in gas mileage or performance. I have used 87 in cars that have required premium for over a million miles and have not had one problem.
A previous post of mine on the subject.
I always revert back to two MIT graduates that are car mechanics who had a syndicated radio show called Car Talk for 35 years.
http://www.cartalk.com/content/premi...egular-0#myth4

From the USA Today:
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.

Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.

All this being said to each his own.

Droid13

Back about 11 or 12 years ago Toyota got the "no-no" finger wagged at them for advertising HP figures on cars based on premium fuel when regular was also acceptable. With a typical engine today, my gut says the difference comes down to what the marketing dept says should be the fuel recommendation, not the technical dept. The calculations come down to product placement, will potential customers be enticed by higher HP more than being put off by a premium fuel pseudo requirement.

05RollaXRS

When I purchased the car 3 weeks ago (and test drove it), I was surprised that even in sport mode, this 2014 RX450h felt sluggish, lazy and slow unless you really got on the power. Even when I went full throttle, it never felt the claimed 300 HP. Of course, when I decided to purchase an RX450h, I knew I will ONLY use premium like do on my other cars that require premium all these years.

My suspicion when I got the car as I had written in my review that the previous owner was using regular fuel. How else could I reconcile it feeling slower and less responsive than my 2008 RX400h I just sold? I never asked the previous owner when he handed me the car with a full tank of gas. Today I ran the tank empty and put Octane 94. While the computer is still learning, I can tell you the difference is pretty astonishing. The engine feels completely different, which confirms the fact that it had Octane 89 during my initial ownership and test drive. The throttle response in sport mode has improved drastically and when I dip into the throttle half way, the urgency to accelerate is much more immediate.

Just wanted to see if you guys have had similar experiences of regular fuel vs octane where it massively pulls timing to prevent pre-detonation (due to high compression). Assuming the previous owner had been using Octane 89 for most of his ownership, does it cause any damage to the engine? So far, the engine feels great and like brand new despite 190K KM. Appreciate the input

Droid13

Whenever I drive to the cottage I use premium, when I drive anywhere else I use regular. The effect is noticeable tank to tank. The cottage trip is 2 1/2 hours mostly on single lane country roads with limits up to 80kph (50mph), but the traffic flows anywhere from 60kph to 110kph depending on who's in front. Thus, I need power to pass. This is the only time I've ever seen a driving advantage to premium. If I need to pass (and sometimes that means multiple cars depending on what is going on), pedal goes to the floor and stays there until I get by, it needs to be quick as possible and sometimes at a good clip. When I do this with regular fuel, I can tell the difference because when I start to let off the gas pedal (say from 100% to 90% throttle) the engine power actually increases. Its a very weird feeling to have the vehicle accelerate as the gas pedal is lifted, but as you say this is the effect of the computer adjustments for lower fuel octane. Premium gives me best power right up to 100% throttle, regular I'm only good to up to 90% throttle before the power curve flattens and actually goes negative.

And to me this makes perfect sense. Sure, you can look at the engine specs and say "this is a high compression engine and always needs premium", but context is everything. The physical compression ratio is only relevant at very high throttle settings when the cylinders can take a maximum charge of fuel and air and cylinder pressure is highest on compression. At other throttle settings cylinder pressure on compression is lower. Also the Atkinson engine in the RXh is also specifically designed to reduce the amount of fuel/air mix into the cylinder even lower than regular engines for efficiency. This all boils down to premium is great at max power when cylinder pressure is highest, otherwise its not really doing much unless it has better detergents or (as I've seen at some stations around here), has less ethanol in it. Since I almost never drive with the gas pedal held to the floor except when going to the cottage for passing, I don't use premium outside of those circumstances.

05RollaXRS

Cool. Thanks for the input. I was checking to see if there were any long term effects, but from you are saying it should be fine as the computer adjusts for it. The engine drives well almost like a brand new car. Definitely much better throttle response and don't need to dig in much when accelerating into traffic etc. I agree at full throttle the car does feel to be putting out noticeably more power with the Octane 94. I will also notice how my L/100 KM change with premium. Like in the RX400h, I will continue to put Octane 94 as I think it makes the throttle more predictable especially when I have the two kids in the back in their baby seats and wife in the passenger seat. With all of that extra weight, based on the gap I get to merge into traffic, the throttle response would make it more safe. Cheers

NickSP

In my 7 month experience with the RXh, I get very good performance from putting 89 Octane. I can tell the difference between 87 and 89. The mpgs and the driving is better. The one thing that suffers more from 87 is mpgs. The performance with 91 is better but not that noticable. I usually cycle by putting in 91 every now and then.