My newly acquired 04 doesn't seem to be getting the mileage is should. I has 90K miles, I drove it a little over 300 miles this weekend and the dash monitor rose to 18.9 at one point. But when I filled up and checked it the old fashion way....I got 15.9. This was 90% highway driving at 70 MPH. Shouldn't it be better than that?

I got less than 300 miles from a tank of gas.

What do I need to check to try and resolve this?

Has anyone tried the E3 spark plugs?

Thanks

 

My truck would average 19-21 MPG at that speed, hand calculated. But, then again, my truck just turned 19,000 miles.

 

You're about do for a spark plug change anyway (100k mi). The platinum OEM are fine. Also make sure your tires are inflated properly. When was the last time your engine air filter was changed? Have all of your fluids been changed i.e. differential fluids, xfer case? If I didn't know the maintenance history of the truck I bought at a minimum I would do all of the above, all of which could have an impact on mpg's.

 

I plan on doing a full maintenance on it this weekend. So hopefully it will help. Tires are inflated above the recommended 32psi at 37psi.

What type oil do the xfer case and diffs use?

What about the transmission? I am thinking of having it flushed.

 

Lexus does not recommend changing the transmission fluid unless an inspection turns up something or you tow or you offroad - your transmission contains Toyota WS lifetime ATF. I am sure you know this already, but your tires may start to wear unevenly if overinflated.

Here's a good thread regarding changing the differential/xfer case fluids. The "search" function is a useful tool if you have a particular question.

https://www.clublexus.com/forums/gx-...-not-hard.html