sktn77a

iTrader: (2)

Hi all:

We have had our 1999 RX300 AWD from new. It's always delivered about 22mpg in mixed city/highway driving. Over the last couple of years, the mileage has gone down to around 18mpg and, most recently, we've only been getting 16mpg. Odometer reads 146,000 miles, car is maintained well, air filter is new, plugs are pretty new (20k miles ago), tire pressures 36 all around and the car drives like new. Just crappy mileage.

Any ideas?

Lexmex

One thing I have been playing around with is certain oil additives to help the piston ring (which get worn down). About 500 miles away from an oil change, I will dump out some oil and put in some Restore Oil additive. About 100 miles away from a change I will then had some Lubro Moly (called Liqui Moly in some places) Motor Oil Saver. The Restore will help smooth down the cylinder walls and then the Lubro Moly will help in regenerating the piston rings. I then do the oil change with some Lubro Moly Engine Flush (though sometimes I will use some ATF or Gunk's flush works well, too), and then change the oil. Usually that gets the pressure up and I have noticed an increase in MPG after that. I have practically new A/F sensors and everything else is kept quite clean. MAF sensor is about 3.5 years old and is kept clean and I use about 38 psi in my tires. Only other part of the equation is that I use a short ram air intake, though I am in the process now of selecting that some aluminum intake pipes for another ram air project that should help improve the combustion and MPG a bit further, but I do know that as our RX300s get older, the combustion area can be an issue.

sktn77a

iTrader: (2)

Yeah, I was thinking maybe engine wear. Performace is obviously not quite what it was when new and this might be the cause. Do these products actually work? (I'm always skeptical of "snake oil" products)!

rx300mm

My 2001 gives me average 17mpg, it's more city driven, done 100k miles. I will be very interested to find if I can improve the mileage.

hypervish

In city I usually get about 18.1 mpg (that's with aggressive driving), regular driving I can achieve a steady mpg of about a little more than 19.

Highway varies, if I drive how I usually do (fast, aggressive, lot's of downshifting) I get about 22-23mpg. If I take it easy, I can get 24-25mpg, the most I've ever got was around 26mpg.

The mpg is both calculated by the computer and by me. I've found the computer to be within' .2mpg always.

Lexmex

Sorry, been on the road for the last day.

Some products only work when you have a certain condition. I don't run an air filter (but then again, I don't have my ram air system set up anymore, but new one coming soon), so for me it has been trial and error with these products, but for me, I found they worked. The Restore is relatively cheap along with the other product mentioned.

Another thing I noticed is that when my last battery was in its waning months, my performance also suffered. I even got a flashing CEL for a misfire, and I knew this was battery related (infamous 1:00 a.m.) and nothing wrong with CEL after I reset the CEL.

lexus114

Ron, you still runnin no air filter?

Ryan

mckellyb

It may not have 'thrown a code', yet, but I'd wager you have a failing oxygen sensor.

Sandhopper

No air filter??? You are sucking dirt into the motor... You probably are getting crappy mileage because you no longer have rings on your pistons or you have bored over your cylinders without the oversized rings and pistons so you are likley losing compression.

Lexmex

Oh, I am not getting crappy gas mileage at all. I get about 19 in the city, and run about 25 on the highway, more if I use cruise control. The method I described above I started to do in Mexico City (will get to that). I also don't get any oil consumption when I run 7500 mileage intervals (I want to run 10K next time since most of my miles over the past few years have been highway). When I do that method, it increases it just a slight tad, not much, but I noticed a bigger bump south of the border.

However, you are right about not running an air filter, but it came down to a dilemma I had in Mexico City.

There, I used the ram air system from about early 2005 onward. Before that, I took no air filter over dealing with continued crappy issues with low oxygen at high altitude. My RX300 moved like a cow up hills. I used to get really crappy gas mileage (like 10 to 12 mpg when I first moved to Mexico) and started to get it up to about 16 or so on average by the time I left with very predominantly city driving. Gas prices (I was there from 2002 to 2008) were similar to what we face in the U.S. now, so doing what I did was quite welcome in the wallet. There were over the years a few other RX300 owners I encountered in Mexico City (Lexus is not sold there so this was a rare treat) and they reported similar crappy MPG. Granted, that air was foul, but so was paying through the butt with crappy gas down there. The additives were a response to deal with that issue with the air.

However, the ram air system didn't pan out when I got back to Florida (too much air causing P0171 errors, jerky IACV), and I disconnected it, and yes the lack of air filter was on my mind there running a ram air system from the bumper. Given it doesn't suck up from the bumper anymore, there hasn't been much of an issue. About my only complaint is the 10% ethanol in the gas, but I'll take that over the high sulfur garbage I had in Mexico.

I have a new air intake design I plan to implement shortly (been parts shopping this week and hope to finish by end of August).

C-Stone

We have 135,000 on our RX300 AWD. Within the last year our mileage began to consistently go down... about to where you mention. I noticed what felt like warped rotors when braking. So I replaced the front rotors and pads. When I did this, I cleaned EVERYTHING up with a wire brush, brake parts cleaner, etc. It all needed it. I think the front rotors were on their last leg and were possibly causing more friction with the pads than normal. Gas mileage went back up to where it was before.

Rivitup

What Octane are you guys using

clevercat

check your oxygen sensors. I had same problem. ECU did not throw code until both oxygen sensors were dead.

hypervish

Only the best for my Lexus... 93. LoL

mckellyb

REDACTED.

Was thinking of another vehicle we have.

I'd use 91/93, if possible, though electronic spark control should prevent damage.