Does the GX require premium unleaded, or is regular unleaded fine? I don't see any mention of premium in the owners manual or in the fuel filler door....

Thanks

Have you searched the gx forums ? http://us.lexusownersclub.com/forums/index...act=Search&f=28

Always loads of info there.

You don't say what MY you have. I have an 06 & the OM states premium, but regular can be used if premium is not available.
When I was doing research prior to buying the vehicle, using the Lexus.com website, the vehicle comparison feature was powered by edmunds.com & it stated that the vehicle (GX) used regular unleaded.

Btw, the sticker inside the fuel door of my 06 states Premium.

I also reviewed the Edmunds info and found the same thing. My GX is a 2005 and does not have a sticker inside the fuel filler door......owners manual dances around the subject, but does not explicitly state one or the other.

I just took a 2000+ mile trip in my 2006 GX on mainly flat highways, and played around with fuel grades for kicks. The premium cost more, but got much better gas mileage so it outweighed the cost.

Basically, in a modeern high-compression engine designed for higher octane fuel, the electronics will retard the timing if you use lower octane, and you will need more gas to create the same amount of power as a higher octane gas would be capable of creating.

Most times, using a lesser octane (cheaper) gas will not save you money in an engine designed to use a higher octane fuel in the first place. Plus, the higher octane fuels tend to have a better mix of detergents/additives to keep everything running smoothly.

For instance, in one very long stretch of flat road, 91 octane "Premium" gas got me 18.5 MPG and 89 "Plus" got me 16.5 mpg... I went back and forth, and the results were the same. Didn't try the basic "low-grade" 87 octane.

There is a difference here in the engines in differing model years. They upped the compression ratio for the 2005 model year, which would make the use of 91 octane more beneficial. I have a 2004 and have experimented with both 91 octane and 87 octane. For normal driving, I have noticed no difference at all...not in performence or mpg.

03s and 04s don't require premium. when the engine got upgraded to VVti then Premium was required (05s and newer).

How big is the tank? Just wondering.

The 05 doesn't require premium either. The manual states, minimum octane 87, for better performance, use 91. I dont understand, the 05 and the 06 have the same engine, the 06 requires premium and the 05 does not. The 06 4runner V8 has the same engine, but it does not require premium either.
I just try out the 1st tank of 87 yesterday, so far so good, didnt notice much difference.

We got an 07GX a few weeks ago. The first couple of fill ups were with 91 octane California gas. Since the car is basically a people mover, performance is not as high a concern. I'm planning on switching to 87octane full time. Any problems at all with 87octane?

I have a 2004, and I use only 87 octane now. I have never had a problem using it. I notice no difference at all in performance or mpg when switching to 91 octane.