As I write this the jury is still out. Decided to put 87 octane fuel in the 2009 RX 350 and one of the first things I noticed IMMEDIATELY was the engine knock gone. It now practically purrs. Let me give you a very obvious example. It no longer sounds like a diesel engine. Prior to this experiment upon cold start up there would be a loud knock, knock, knock sound. As I started it up a few minutes ago it's 58° and it's purring. While not completely gone it's what I call "purring".
Also while on cruise control going uphill I notice a stronger smoother "pull" on 87 octane as opposed to a herky-jerky hard shifting sort of pull as it tried to maintain the speed I set.
The SUV pulls strong on stops & starts and now the only thing left to be seen is mpg.
This is only going on 3 days but the observations were so obvious it's startling.

Soooo, what happened?
Cheers

 

Yes. The engine seems a lot smoother and softer, with revs without vibrations. I attribute this to the loss of power due to the lower octane.

 

What does the handbook recommend for that engine? Unless there is an issue with carbon build-up in the cylinders and valves that artificially creates a higher compression-ratio, usually, an engine will run best on what is recommended for it.

 

Most Toyotas have always been designed to run best on the highest octane possible. Usually research 91.

For example, the 2005 Tundra makes 282 HP on 91 octance, BUT the vehicle is fine on lower octane. But a 2006 Tundra v8 will make 271hp on a lower octane and it is rated at that the because of SAE specs.

If you put 91 in a Land Cruiser you will make 383hp which is the same as the LX570 which requires premium fuel and is SAE rated at 383hp.....where the LC is rated at 381hp on regular.

Overall, you RX should NOT be knocking on the lower octane. But your RX will run at perfect spec on premium fuel.

What is the VIN on your RX? Canada or Japan made?

 

Is your RX premium required or regular required?

 

That year requires premium, for MY13, Lexus changed the ES and RX rating to regular 87. Modern engines though are smart enough to adjust for knocking and pinging even if it 'requires' a higher octane.

 

I've run 87 in my 1992 SC300 once because the gas station in the boonies was out of 93. It ran fine, but I drove it conservatively that whole tank. That car is old enough to where I don't know if the knock sensor is advanced enough to cut the timing for lower octane fuel and prevent pinging/detonation, or if it is cutting timing on 87, its probably pulling it WAY back and leaving a bunch of hp on the table.

As for something newer like your RX, I say fill it up with 87, just make sure its a top tier gas like BP, Shell, etc. Cheap gas is cheap for a reason, they don't put nearly the same amount detergents in it like the name brand stuff. Paying the extra(or in my case the Shell is the same as the el cheapo gas next door) 2 or 5 cents a gallon is worth it in the long run when you avoid a very expensive mechanic bill for your valves and cylinders being full of carbon.

 

It calls for premium.

 

Makes sense to me. Now the engine sound more like a tap-tap-tap instead of a knock like my friends Ford F350.

 

Yes, modern Toyota can adjust and so can older ones...however that Toyota should run at full spec on premium fuel...and a new one should make the same HP as the 09 on premium as well. What HP rating is 09 rated at?

 

Minor point, but I think it was MY2012 (the last year for the previous gen ES350) when regular became OK for the RX and ES.

Having owned a 2007 and 2010 ES350, I always thought it was odd that premium was required/recommended "to achieve advertised horsepower". At the same time regular was recommended in about 6 Toyota models using the same engine and generating 268-270 hp. The skeptic in me wondered about the timing of the change. The economy hadn't recovered yet, and competitors were coming with vehicles where regular was recommended, and then all of a sudden regular was OK for the ES and RX each loosing about 4 hp. in the process and EPS estimates remained the same.

In any case, it was a good move on Lexus' part. I used mostly regular unleaded in both cars and have always felt you can't go wrong either way and it's a personal choice as to what grade to use in this case.

 

OK looking at page 424 of the owners handbook it calls for 91. Then go further to page 433 and it looks as though using 87 is OK.
That pretty much answers if it's OK.

 

What that usually means is that the engine's computer, like most engine-control systems today, adjusts the spark-timing and fuel/air mixture if it detects pinging/knocking in one or more of the engine's cylinders from running lower-octane fuel. That will sometimes cost a couple of HP or ft-lbs. of torque, or maybe have a small influence on fuel-economy.....but, in most cases, not a difference large enough to really notice. Many engines today are really intended for 91 octane, but the engineers, knowing that sometimes people can only get crap low-octane gas if they are across the border in Mexico, or just don't want to pay the extra money for premium, built in those computer-adjustment controls for the time the engines don't get the 91-octane (or if there is pinging from other reasons).

 

I think your right about the economy having some effect on octane recommendation. I'll gladly sacrifice a few HP, $$$ and quoted SUV any day.

 

first world problems.