kiwi

I have searched the threads, and haven't really found an answer

i am getting incredibly poor fuel mileage. i have a 2004, sport package, AWD. with 208,000 KM / 130,000 miles.

i drive conservatively in an effort to better my mileage, i am the only driver.

its only going to get worse, when they go to winter gas and my snow tires get put on in a month or so. (i live in Quebec)

my tire pressure is checked 2-3 times a month, i have tried different grades of fuel. Air filter has been changed, i use royal purple oil, changed on time (maybe even a little too often). just ran a can of injector cleaner through my last tank, no real improvement. (royal purple Max clean, 20 bucks)

the car otherwise runs perfectly fine, no engine lights, no rough idle, nothing at all.

will replacing the spark plugs help? its been a while, and i tempted to do it anyway.

even though i dont have an engine light on, i am tempted to replace all of my oxygen sensors. im leery about this because its very pricey.

Anything else i should be inspecting?

i know some cars have known areas which get gunked up with carbon and need to be disassembled and cleaned manually to remedy, does the RX330 have this??

any suggestions welcomed. i check the threads daily, so if more info is wanted, i will reply.

pablo87

I have a 2005 with 152,000 miles. I get 12.7L/100 (12.2 per display) driving at an avg speed of 25mph (per onboard computer). If I'm stuck in traffic a lot, such that my avg speed is less than above, mpg goes south. And vice versa. All on 87 octane.

I also tried a lot of different things to get better MPG - tire pressure, chg pcv, clean maf, clean tb, chg air filter, techron f.i cleaner, changed plugs, change fuel octane all to no avail (although if its hilly where you drive, I believe higher octane gets better mpg as the RX is under powered on 87 - at least mine is).

Finally, I tried 4 things and now I have better mpg. Which one did the trick I can't say exactly:

#1 liqui moly MOS2 in the oil - moly additive. Definitely quieted the engine.
#2 liqui moly Ventil Sauber - valve cleaner in the tank. Felt like better mpg right after.
#3 liqui moly jectron - fi additive in the tank. Butt dyno says no improvement.
#4 toyota 0w20 synthetic oil - felt quieter, smoother when cold. Possibly better mpg.

I get the Liqui Moly stuff from Napa in the States.

kiwi

i will check out the liqui moly stuff for sure, hopefully its available up in canada.

i have cleaned the MAF sensor, i have also changed the transmission fluid and differential oils as well recently.

i also recently did a brake service, all brake calipers are working properly, the slider pins are also free and moving.

diverchris

Hello,
I agree with everything that has been posted. A few things come to mind:
1. change the spark plugs, I had mine changed at 190K kms they were extremely dirty and the gap was out I just cannot remember how much they were out.
2. have you checked to see if you have any seized callipers, especially the rear ones, I've had two seize up on me and I have my brakes serviced annually
3. I think a forced induction cleaning, Seafoam or similar product through the vacuum line might be something to consider prior to changing the spark plugs

My thoughts are if no CEL's are present then the drag is somewhere else, like seized calibers

I hope this helps,
Chris

kiwi

calipers are good.

i have cleaned the Throttle Body as well, no dis-assembly, just removal of the intake/air filter box to access it.

roadbike56

With 60K on the clock we're getting 21.6 MPG overall in North Carolina. If mine fell to 15MPG, it would be in the shop for a complete diagnostic. I wouldn't do anything other than a tune-up or new airfilter without a complete diagnostic.

Rainbird

Perhaps defective shift solenoid valve with no up-shift on the transmission from 4th to 5th. Check for ODB trouble codes.

lexsc4

My wife 08 RX350 AWD with 90K miles average around 15 MPG. All short local trips, running errands and pickup/drop kids from school (2 minutes drive, so engine is barely warmed up) and she drives like a snail.

All tires pressure are checked once a month, brand new air filter last month. Transmission drain and refill every 20K miles. The most we ever got was 22-3 MPG going from SF to LA, average ~70 MPH.

Oh well, at least we fill up once every two weeks.

08 RX350 AWD (wife)
08 Avalon Touring (mine)

kiwi

transmission shifts beautifully, no issues whatsoever, the fluid looks fantastic too.

checked for codes yesterday, nothing at all.

gonna go with new plugs within the week, hopefully the rear bank isnt so bad to access

kickin8

iTrader: (1)

what kind of tires are you curently runing?

did you also drain/refill your differentials?

JasDmw

Didn't look closely above, but are you using premium fuel? Once put regular in mine (by accident) and the mileage tanked. Once that was gone and refilled with the good stuff, mileage went back up again. Am averaging about 21-23 MPG.

kiwi

as already mentioned, the differential fluids were changed recently.

as far as which fuel i use. i experimented a few years back, and kept solid track of mileage. there was no real difference in mileage between 87 octane to 91. only a slight power difference, which could have been mental. so i use 87.

given the circumstances, i will give premium a go. where i live now, they actually have 94 octance available, so maybe i will try a tank of that.

tire, i use OEM size (18"). Bridgestone Alenza.

kickin8

iTrader: (1)

I'll probably take 2 tanks before you can tell the mpg difference.

Bridgestone Alenza - used to be ~18 mpg. It went up to ~20mpg after I switched to Bridgestone Dueler H/L 422 Ecopia

kiwi

update.

i have now installed my winter tires, which will prob make the mileage get worse.

i have replaced the spark plugs, PCV valve, changed air filter (i also cleaned everything as i went :TB, MAF sensor etc)

i also refueled (gas light was on) with supreme fuel, (94 octane)

thus far (approx. 150 km) no change. in fact its worse, prob because of winter tires and winter gas. i am doing about 17L/100km.

this is by far the worst i have seen the milage, previous winters were around 14L/100km

i am going to do at least 2 tanks, which is about 700km before i do anything else.

my next step, which seems my last and final option, is to replace all the air/fuel and oxygen sensors, which will cost approx. 450$.

any suggestions are welcome

RamAirRckt

For me, I would data log it (if you are into tuning), see what is going on. Most mechanics don't know what to look for either. They replace parts if there is codes.

I would put on a data logger (http://www.scantool.net/obdlink-sx.html) and software (http://www.scantool.net/scanxl-std.html) and log what is going on. Watch CAREFULLY at the O2 voltages and the LTFT's. This is where I expect you to see something. With the crap ethanol gas it tends to push things on the lean side (but the ECU compensates), but if there is a bad fuel pressure regulator, you will see BOTH banks (left and right) showing on the rich side. It might still be to a point where it isn't setting codes, but it could still be on the pig rich side.

Note, please don't waste time and $ on an ELM327. Everyone will tell you it is good, it is junk. Trust me. I have used ELM323, ELM327 and the OBDLink SX which is based a far superior chip. Compared to what I use when I tune GM cars/trucks, the SX is junk, but for the Lexus it is great $/to what you get. If you are code reading the SX is ideal. OBDWiz comes with it, it is ok, not great, but ok. ScanXL is 1000% better. But likely overkill for what you need, but if you have $$ to toss into it, I would.

FPR (Fuel Pressure Regulator) is often damaged by the crap politician mandated ethanol fuel we have here and even a pinhole at 4 bar fuel pressure will leak fuel in the vacuum hose and the engine will be sucking up fuel that isn't calculated into the AFR calculations.

Sometimes you can see fuel in the vacuum hose (if Lexus has one like that), but often you can't, but it is there.