Gasoline Grade For Rx400h

[RX400h]

The manual says use 87 octane or higher

Which is why I stated:

If the owner's manual says to use a higher octane, then listen to the Good Book.

I am not familiar with the requirements on a 2006 RX400, but if you say it recommends 87 octane, then your ok, as using a higher octane then what is required is useless also. Only engines that need higher octane, or have knock issues, need to use higher octane.

As for the fuel mileage, I would attribute the difference in MPG's to the way you drive during the summer vs. the way you drive in the winter as the major contributing factor.

The manual doesn't "recommend" regular fuel, but it does state that 87 octane may be used. It goes on to state that higher performance will be available if higher octane fuel is used. The reason why I bring this up is that it is unlikely that following the manual would result in damage to the engine. Certainly, if no mention of 87 or 89 octane is included in the manual, but a specific requirement that 91 octane fuel be used, is, then pumping in lower octane fuel is asking for trouble.

[smooth1]

The manual says use 87 octane or higher

Which is why I stated:

If the owner's manual says to use a higher octane, then listen to the Good Book.

I am not familiar with the requirements on a 2006 RX400, but if you say it recommends 87 octane, then your ok, as using a higher octane then what is required is useless also. Only engines that need higher octane, or have knock issues, need to use higher octane.

As for the fuel mileage, I would attribute the difference in MPG's to the way you drive during the summer vs. the way you drive in the winter as the major contributing factor.

The manual doesn't "recommend" regular fuel, but it does state that 87 octane may be used. It goes on to state that higher performance will be available if higher octane fuel is used. The reason why I bring this up is that it is unlikely that following the manual would result in damage to the engine. Certainly, if no mention of 87 or 89 octane is included in the manual, but a specific requirement that 91 octane fuel be used, is, then pumping in lower octane fuel is asking for trouble.

I beleive this would be due to the Synergy drive system. The engine never really sees WOT load conditions, where engine knock is the most dangerous. Instead it engages the rear electric motor to help with that, and under regular driving conditions would only use the forward electric motor to assist. I would imagine that in the RX 400h, fuel mileage takes lead design philosiphies over any aggressive timing and fuel maps. So I can easily understand that 87 octane allowance. Remember, we really can't compare a hybrid to a regular gasoline engine. Regular gasoline engines have to be mapped for full throttle conditions, which can greatly influence the intitial timing and map settings, whereas the Hybrid doeasn't really have to account for that.

But even so, if I owned an RX 400h, and reading the owners manual, I would determine that 91 octane in this case might be the better choice. ( With no Ethanol in it if possible. )

[08rx400h]

I experimented with 87 and 89 grade during a 400-mile round trip down in Florida. The MPG dropped about 2 miles when 87 was used. On a separate occation, when 91 was filled, I didn't notice any advantage. I go with 89 (mid grade) ever since.

[smooth1]

But Florida has a Ethanol mandate now in effect. So do you attribute the lower fuel mileage to that or the octane difference?

[silvercorvette]

This was a copy and paste from the bottom of page 13 from the PDF

http://www.lexus.com/hybriddrive/pdf/HybridPcktGuide.pdf

• Use Premium Octane Fuel: Using the proper fuel (91 octane or

higher) will help improve fuel economy and performance.

[RX400h]

...from my 2006 RX400h owner's manual:

Select Octane Rating 87 (Research Octane Number 91) or higher. For improved vehicle performance, the use of premium unleaded gasolene with an Octane rating of 91 (Research Octane Number 96) or higher is recommended.

As you can see, 87 octane is perfectly acceptable (for a 2006) if "improved vehicle performance" is not necessary.