My understanding says you will loose 4 mpg (maximum) if you are a driver who paddles faster for faster pickups. In other words, 91 grade will help you if you are paddling faster (for faster pickups) after signal lights. And you will still get the good mpg.

If someone is driving normally, like paddling at the regular pace etc, he or she will not see any reduction in mpg at all due to use of 87 grade fuel.

 

Can anyone looked up on the manual so its a accurate quote? I'll try to report it later when I look it up, but can anyone actually know it from the manual?

 

Here is what my 2010 450h manual says (direct quote):

Your vehicle must use only unleaded gasoline.
Premium unleaded gasoline with an octane rating of 91 (Research Octane
Number 96) or higher required for optimum engine performance. If 91
octane cannot be obtained, you may use unleaded gasoline with an octane
rating as low as 87 (Research Octane Number 91). Use of unleaded gasoline
with an octane rating lower than 91 may result in engine knocking. Persistent
knocking can lead to engine damage and should be corrected by
refueling with higher octane unleaded gasoline.
At minimum, the gasoline you use should meet the specifications of
ASTM D4814 in the U.S.A. and CGSB3.5-M93 in Canada.

But, as many members have reported the car runs just fine on 87. I personally will use 91 in mine.

 

I have used all three and did see a little decline in mpg .5mpg from 93 to 89 and 1.5 from 93 to 87. So it is up to you and you alone to what you want to put in your car. But I on on the gulf coast so there are no hill here and we do not see very cold winter days until mid Jan- mid Feb then winter is just about over. It is 70.4 °F here now and they say that it Feels Like 76 °F. Got to love the GOM.

 

I finished a two month, 10,000 mile vacation in September in our 2010 RX350. Once we reached Canada and saw the goofy prices they wanted for Premium I started using Regular grade and saw no decrease in performance or fuel mileage (in fact a slight increase). I seriously doubt any significant changes were made in the ECU setup for 2012, only a realization by Lexus that telling customers the vehicle requires premium fuel was no longer a positive attribute to sell vehicles. Everyone can do what they want but I'm using Regular.

Oh, since a picture is worth a thousand words here is a shot of my performance representing 10,000 miles. Mileage at start of trip was 4,511 mi, at end 14,602 mi. Regular fuel started on 8/14/11, data point for 'Today' was 9/15/11. I attribute slight increase in mileage when switching over to regular to continued break in of engine and more sustained highway driving during second half of trip:

 

This are exactly my thoughts. It used to be that fuels made a difference to performance and it was a status symbol to use the expensive premium fuel. It gave people an elitist feel. This was the way it was when I owned my last Benz., but after a while you figure out there is no benefit.

Lexus is going for lower cost of ownership which is a great marketing strategy. It would be hard for them to tell you can use regular in the Toyota Highlander and then say "Oh you have a Lexus, that gives you the privelege of of paying more for fuel" This is exactly what the GM at my Lexus dealer said to me earlier, it was a marketing thing.

Here in Canada, a country that exports more gas than it uses, 87 is $ 1.11/liter and 93 octane is $126/ liter. That works out to $4.75 a US gallon or almost 60cents a gallon more than the 87 octane. The one thing you need to watch though is the lower octanes contain more Ethanol which reduces horsepower. The Premium however does not have ethanol which gives it more horsepower. Not a huge deal as I will be driving a Hybrid.

For me the difference in price between 87 and 93, makes a difference of about $600 a year as I spend about 6K a year in gas. I hope to almost half that from my present Envoy, which although has been great as far as a vehicle goes is brutal on fuel, when I get my 450H. Green peace would be happier if the Envoy ran on sliced dolphins than fossil fuels. I average 15mpg.

 

Based on this discussion thread, can anyone think of any reason why Lexus would not want to issue a technical bulletin to all 2010 and 2011 RX owners revising their original requirement to now using regular (87) instead of premium (91) gas??

 

This was from a Globe and Mail article back in December. Thought I would share his perspective, the better fuel mileage on Premium fuel was interesting. Have any other RX350 owners in this forum tracked this as well?

Here is the exerpt from the article:

“The use of regular fuel in a modern engine where premium is recommended will cause little harm. It will result in a slight decrease in performance and fuel efficiency, however.
Before the arrival of powerful computers and sensitive sensors, the use of regular fuel in an engine designed for high test would result in what is known as detonation, engine knocking or pinging. This occurs when pockets of the fuel-air mixture in a cylinder ignite as a result of heat and pressure rather than a spark (plug).
This can lead to catastrophic – expensive – failure through holes punched in the pistons or damaged cylinder heads.

The cures are higher-octane fuel or the prediction and detection of “knock” and subsequent change in ignition timing. Today’s sophisticated engine management systems – made necessary by the need to have engines police themselves for exhaust emissions – are quite capable of reducing the risk of engine damage from lower-octane fuel.
Many companies that sell vehicles in a wide variety of global markets have to make allowances for really poor quality fuel, thus the insistence on high test.

Having said that, premium fuel commonly contains additives not used in lower grades, chemicals that help clean the combustion chamber. And, don’t forget, that while it appears using regular fuel saves money, you are using more fuel or going fewer kilometres on each litre of fuel.” Globe and Mail Dec 5, 2011.

I'm currently running our 2010 RX350 with Premium (thankfully we have a Costco fuel station close by!) and was encouraged that I may be getting better fuel economy/milegae with my engine performance.

 

I have also read that you will get improved milage with premium fuel. However at a 20 cent a liter premium here in winnipeg (75 cents a US gallon) I can not imagine that I would be better off using Premium. That is an almost 20% premium from Premium. I doubt I will get 20% better milage.

That being said our premium is still only 91 octane so we are not even getting the good stuff.

 

IMO, adding a bottle/can of fuel additives periodically accomplishes the task of maintianing a "cleaner" fuel delivery system vs using PREMIUM fuel on a regular basis. It may be nickles and dimes but I've found satisfactory fuel comsumption/mileage with regular grade gasoline.

 

Our RX gets the best mileage on Hess Premium fuel- 20.5 mpg. It does not like Sunoco Ultra or Costco gas. I see a decrease in 1.5-2 mpg.

 

Winnipeg Fuel prices....yikes!

Calgary Regular is 98.5/L and Premium is 106.9/L at Costco Goasoline....only an +8.1% spread and hoping I can achieve about 10% better fuel economy mileage with Premium. As we don't have Hess here, I'll track mileage with Costco versus Shell and Petro Canada premium to see if there is a difference.

 

I just got a 2010 RX, and I have been getting over 21 on regular gas (combined driving) - wife has a 2007 RX and she gets about 20 mpg on regular. On highway trips i get 23 mpg in the 2010, so i see no reason to try premium. Even with 10% better mileage - I see it as maybe $6 per tank, which is 2 gallons of fuel and 40 more miles - basically an even trade.

 

I filled up today and paid $106.9. The premium was $119.9. There is only one costco here that has gas but it is on the other side of town. That being said I am averaging 26 mpg (US) over my first 2000 KM's. I expect a big improvement with break in and summer temperatures.

 

It's partly correct and partly incorrect.

http://www.cartalk.com/content/premium-vs-regular-1
http://www.cartalk.com/content/premium-vs-regular-0

TL;DR "Our advice is to ignore any sales pitch about the super-special detergents that come in the premium-grade fuel."