Lexus RX400h - 87 Octane vs. 92 Octane

Old 06-15-2006, 11:49 PM
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Default Lexus RX400h - 87 Octane vs. 92 Octane

Is there any advantage to using a higher grade fuel with a higher octane rating?

I understand you will have slightly better preformace. Would you damage your car if you used 87 octane instead?
Old 06-16-2006, 04:00 AM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

What does the manual say to use? That's what the car was designed for. Up or down will not damage anything- the computer can handle it all, but you may not get optimal FE or performance.

High octane fuel takes higher compresison to ignite, minimizing 'knocking' in old engines without knock sensors to retard/advance spark timing. That was the primary benefit back then.

Today, engineers can take advantage of this if they explicitly design the engine to use premium gas to increase power. It has no effect on FE or performance in a modern engine that has properly functioning electronics and was not designed to use high octance fuel. The electronics will notice the difference, and adjust timing accordingly to recreate the 'ideal' combustion conditions you would normally get with regular fuel.

The only exception is if your engine is particularly fouled. Most premium fuels have a higher Ethanol or other detergent content which will clean the fuel system (ethanol is a good solvent for the type of gunk found in fuel lines). This will restore some performance and/or FE after a few tanks. But once the system is cleaned, go back to regular.

Last edited by gonavy; 06-16-2006 at 04:05 AM.
Old 06-16-2006, 08:44 AM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

While it is true that the electronics can accomodate for most changes in octane, using a lower grade in a vehicle designed for a high grade can (doesn't always, but can) result in pinging. Pinging can damage your engine since it is really the piston wobbling in the cylinder.

So, use the lower if you want, but if you hear pinging, then put in the more expensive stuff.

I am not disagreeing with gonavy, but think it is important to know what the symptoms would be if any damage was being done. And don't worry, if it pings you will know it. It makes a real racket!
Old 06-16-2006, 09:54 AM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

The manual says 87, but then it says use 91+ for higher performance.
Old 06-16-2006, 03:27 PM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

Originally Posted by SlvrRXh
The manual says 87, but then it says use 91+ for higher performance.
Do you feel like you need the extra performance? My guess is that you won't notice the difference unless you are the type of vehicle owner that is extremly tuned into their vehicle and constantly looking to get just that much more out of it.

If you are happy with the current pick-up and acceleration of the vehicle with regular than no need to spend the extra money. If you feel that having just a little extra umph would make driving your vehicle more pleasurable than go for higher octane.

Last edited by Chilly; 06-16-2006 at 09:17 PM.
Old 06-17-2006, 01:21 PM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

In Lexus RX400h Hybrid Overview
Ten Tips for improving fuel economy
9) Use premium fuel to improve fuel economy and performance
Old 06-17-2006, 03:35 PM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

I definitely notice a difference in power between 87 and 89, but I haven't noticed any better FE numbers... Perhaps 91 octane? However, it gets a bit expensive at that point...
Old 06-18-2006, 01:13 AM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane


im with you. I tried higher octane in my escort, and found no diff in economy whatsoever. Perhaps its cleaner for the enviro or better for the engine however.

Old 06-20-2006, 05:03 PM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

I am on my 7th tank. Out of the first six, four were 87, two were 92. I could not tell a difference between the two during brisk acceleration. It also did not appear to have an effect on the fuel economy. However, some of this could be due to the break in period.
Old 04-25-2010, 01:45 PM
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Default Re: Lexus RX400h - 87 Octane vs. 92 Octane

The engine in the Lexus RX400 is EXACTLY the same as the one used in our '06 Highlander Hybrid. These engines are DESIGNED to work to their optimal fuel efficiency using regular (87 octane) fuel. Studies have been done on the lower vs. higher octane fuels and the ONLY vehicles that get SIGNIFICANTLY better fuel economy on the premium octane are those specifically designed to use premium fuel as their "suggested" fuel. This crap about "better performance" had to of been something invented by the fuel companies.
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