mandyfig

3.5L Toyota Engine requires premium.

Pmkettler

I talked to our lexus service guy today, he said the only downfall with running regular is you will not get the full horsepower and gas mileage might not be as good as if I used premium. He said it is fine to run regular.

RX330inFL

As I noted above, it is OK to try and use for a few tanks to see how things go. If you are happy you can stick with it. Some of the problems individuals have reported when trying to use regular in a 2nd Generation RX350 include but are not limited to:

• Poor MPG
• Sluggish acceleration they found unacceptable when trying to merge into traffic
• Hunting for the proper gear by the transmission.

I run regular in my RX330 and do not notice any measurable difference in MPG in my day-to-day driving when compared to when I tried running premium for an extended period of time. However, when it comes to my long distance trips when the vehicle is normally fully loaded I will run 89 or 93 octane. On these highway runs up and down the various elevations I get better MPG on the higher octane fuel though performance otherwise does not seem to be all that much different. Now, my RX330 is geared to run on 87 octane. This may or may be true for your RX350 which wants 91 octane by default.

takeshi74

Generally speaking, any engine designed for a higher octane should be run at the higher octane. An occasional tank of lower octane -- say, for times when you just can't find the appropriate octane -- isn't a problem for most engines since they have knock sensors but regularly running lower octane than the engine is designed for (especially under higher loads) can possibly lead to issues down the road.

Higher octane fuel in an engine designed for lower octane generally provides no benefit.

Again, these are just broad generalizations and I'm not specifically speaking to any of the engines mentioned in this thread. There are plenty of reputable resources on the matter that you can refer to if you want to dig more into it. Personally, for my higher octane vehicles I'm not willing to run the risk in exchange for saving a few bucks per tank. YMMV. You can always test lower octane fuel in your own vehicle and monitor fuel economy and performance while looking out for knocking and pinging. If none of those are a problem for your vehicle and your usage then you might be fine with lower octane.

Henry1492

I have about 72k miles on my RX.

I get about 18 or 19 mixes city/hwy

I started putting in Premium fuel. 92 I think, and the performance and pickup has improved. Not sure about the mpg quite yet.

LXPearl

If you check the Toyota Technical Information System site (emissions) there is a discussion in the training session on the effect of gasoline grades with Toyota engines with knock sensors (typically all modern engines with emission controls). These engines will adjust to fuel grades and prevent knocking. When the engine detonates, the ECM will adjust and retard the spark, which will negatively affect engine performance and fuel economy under all driving conditions. For engines with advanced ECM (essentially all modern engines), an adaptive memory factor is used to track the signals from the knock sensor. This means the retarded setting will be maintained for an extended period of time, even though a tank of higher grade fuel is used. This "keep alive" memory can be cleared by removing power from the BATT terminal. Unless the memory is cleared, the engine will be operating at a retarded spark condition even while alternating 87 and 93 fuel; so little benefit of the one tank of 93 fuel will be realized. Toyota has used several different EFI ignition systems, and rather than a linear effect of fuel use, these systems now take multiple inputs (fuel, coolant, engine load, etc.) to create a 3D spark map.

What I did to test 87 vs 93 was to do so during a road trip with a loaded vehicle (2004 3.3L 5 spd auto) and use cruise control across rolling hills in OK and KS. The engine never pinged on 87, but it noticeably downshifted more on hills to maintain speed than when I tested it with 93 fuel. Interestingly, the downshifts on 87 seemed more abrupt, whereas the relatively few downshifts on 93 were smooth downshifts. Mileage difference was negligible, about 0.5 MPG better for 93 fuel. I did the same with the LX470, with similar results.

My conclusions from this information was that Toyota had good control of the engine regardless of the octane rating chosen, but there were torque, HP, and economy impacts for using 87 instead of premium. Even a Toyota vehicle rated for 87 will perform better on 91 as the ECM adjusts. This is most noticeable on trips with a loaded car than around town with an empty car. Premium fuel will give smoother torque response, which with a big, heavy vehicle like the LX may be noticeable in city driving, but is clearly noted on trips with cruise control.

Gitchiesus

Bring this old topic up. Was reading all the pages, no clear answer seems it's all just subject to perception. I don't own one, but was thinking of getting an older one to replace an againg audi.
My thoughts were, is it "recommended" or "required" for 2005-2007 models. People will say well it's a Lexus....but seriously at the end of the day, it's a glorified Toyota. And it's like 7 years old,,,,,

I get the premium thing for my other cars, audi and volkswagen tiguan and acura mdx but if it's not required...why waste?

Like my mother in law loves her corolla, wants to keep it....so should she be buying premium gas? Why? Because most users here will say premium is the best...... Not really an answer in my mind.

With gas at $6 a gallon here in canada it would be nice to have a car running regular for once!
Where in the states last week I seen premium for under 4 a gallon, dam!

daryll40

A couple of thoughts in response to the last post. First, premium gas is now under THREE dollars in most of the USA

Second, your comment about using premium in a Corolla implies that premium is better. That was true when I was a kid (I'm 54) but it's not true today. Not only is premium not required for a Corolla, it's not recommended. It's actually worse for the car than the gas it was designed to run on.

Third is that the 2nd gen RX has now been out for over 10 years. You never hear about engine problems. My guess is that if using regular gas was a problem, you'd be hearing about engine problems.

Finally a disclosure that we had a 2006 RX from 2009 thru this past April but we no longer own that vehicle (did get a new 2014 RX).

Gitchiesus

Yes I would never put premium in a corolla. I was only saying that cause most members just say" premium is the best"......
Yes it is worst off by doing such.....
I don't mind paying for premium, but as I get older I can now see the differences between the marketing of these car companies. Just asking why people use premium, when it's not required.
Believe you me, if my bmws had said recommended instead of required.....I would have gladly used regular. But the fuel cap said required.....

tfischer

The Canadian poster did not adjust for the Imperial Gallon or the Canadian Dollar, which would bring the gas prices closer together.
More importantly, a part of the glorification process is a more sophisticated engine with different tuning. A driver's best performance and best mpg (or miles per liter or whatever they use up there) will be obtained by using fuel having the manufacturer's recommended octane rating. A higher octane rating is just wasted money, and a lower octane rating will cause the engine to retard ignition, resulting in unnecessary wear, lowered performance and usually higher mpg. The fact that the car will start and run on lower octane rating does not mean that running that fuel is not harming the car or that you are getting the most for your gasoline dollar. In the long run, it's less expensive to use the recommended octane, whatever that number is.

cdnewton

We use 85 octane (similar to 87 in lower elevation areas) and our 04 RX330 is getting ready to turn 191,000 miles .... it is still running strong. Unless the fuel cap has a label that states "premium fuel is required" vice "recommended", I cannot identify any long-term (11 years old next month) issues of running regular unleaded. This topic is always interesting to discuss.

Gitchiesus

Yes I didn't. 4 litres equals one gallon. Basically, it might be 3.8? Litres to a gallon.
Premium in the US is 3 dollars a gallon? Or maybe even 4?

Premium here is 1.52 a litre....by 4(4 litres to a gallon) Equals......call it 6 or very very close to it.....
Even with exchange, even worse since the US dollar is better than the Canadian dollar right now....
Believe me, I wish I could rent a gas tanker and drive to the states and fill it up to bring home.
When I fill my mdx here in canada, it's usually 95-100..... In the states, I was spilling out gas at 67 dollars....

Gitchiesus

I agree.....I was looking to see what the owners here were saying what is on their gas cap says.
If I see recommended yes I think it totally ok to run regular. But if it states required, than yes you only use premium.
Why waste it if its not required. These rx aren't exactly sporty hi performance SUVs.

BensonRX

I bought my daughter the RX350 a few months ago and have been experimenting with the fuel type. For the first 14 tanks I gave her mid-grade, but have used premium in the last 4 tanks. At this point, it looks like the premium is getting ~1mpg better. I plan to use premium for he next 10 tanks to get a better overall comparison -- I'll report back.

I haven't looked through this whole thread, has someone else tried this experiment over a long time?

FWIW, I use regular in the wife's Pilot and premium in my Audi S4.

jfelbab

After 1 year (about 9,000 miles) in my 2014 RX350 AWD. I'm still mostly using regular as the cost of premium (+$0.40/gallon) makes the added fuel economy not worth the cost. I also have not used 91 octane but a few tanks so the graph is not cast in stone.