SLegacy99

Things to consider:

Outside temperatures
Winter fuel - do they put additives in your fuel in the winter? They do in PA. I lose about 2 MPG in my Subaru because of it.
Tire pressure - again, cold temps = cold tires = lower pressure = lower mileage
Fuel grade - what kind are you using. On highway trips I found that it is more efficient to run 89 than 87. Haven't tested 93 yet.

drvmecrzy

This is happening to me. I've owned my CPO 2006 RX400h for 3 years. I was getting 23-26mpg, then 17-18, now 11-12. This has worsened over the course of 3 months. The dealership has performed multiple ISC resets and it helped the first time ( I was back to 23) but then it quickly returned to 17. Please offer any advice.

rcy

How is your 12 volt battery? If it's weak, you might be losing your ISC reset.

Other factors - tire pressure, gas (brand and octane), dragging brakes (regular and/or the parking brake, faulty computer (as in it's showing 17mpg, but that's not what you're actually getting - consider measuring your fuel economy manually), 02 sensor(s) - if you're not getting a check engine light, they just might be 'lazy'..

drvmecrzy

The 12V checked out ok. I use only exxon or shell gas and I've played around with the octane. Worse with 89 and higher. Tire pressure fine, I calculate my own MPG to be a little lower than what the computer says. It doesn't come up with any bad "codes" when they check it. No light on my O2 sensors i had this problem on a Honda so i know what to look for. What gives?

nopcbs

We just bought a 2008 RX400H w/ 18,500 miles. It is 3 years old (Jan 2009 in-service date).

We had it shipped to us and on arrival the car would not start w/o a jump. It did this two more times before it settled down to starting normally w/ the same battery. I gave it a couple of battery charges along the way. Not sure what the heck was going on.

Anyway, on our first full day of in-town shopping with the car AFTER THE BATTERY NONSENSE HAD ENDED and we got just under 30 mpg (20 miles). Then we drove to a nearby town (more shopping) and averaged 26 mpg in 50/50 mixed city/highway. This is w/o doing any of this ISC resetting stuff.

When you start the car (Ready state), the engine normally turns on after a few seconds, even w/o the car moving.

I am really suspicious of this ISC resetting stuff that seome people are pushing, at least as far as mileage improvement goes. Our battery was clearly VERY weak, we did no resetting and we got near 30 mpg. What will a ISC reset do...get us to 40 mpg?

- nopcbs

prowler97

I notice that as soon as I put on the heat with any hybrid vehicle the engine kicks on even when your parked. This can cause significant reduction in fuel economy because the engine is always on in the winter. However the AC can run on electric and does not force the engine to turn on until the battery is drained. I personally would not buy a hybrid if I lived in a cold climate.

rcy

No it's not. And I live where we get significant cold in the winter months (usually - this winter so far is an exception). This is my third winter with the vehicle - the ICE DOES NOT run all the time when the heat is on - the engine will run sooner and longer when first starting the vehicle to get the coolant up to temperature for climate control. Once the coolant is hot, the engine need not be running to provide heat to the cabin. It will run more often as heat is transferred from the coolant to the cabin in order to keep the coolant hot, but it will not run continuously.

As I've posted elsewere, there is a separate electric pump to keep the coolant circulating through the heater core, even when the engine is off and the mechanical water pump is not providing coolant circulation. This electric pump is specifically there to allow heat while the ICE is not running.

nopcbs

Winter makes a difference how hybrids behave. The engine will run more to heat its coolant and to also heat the car interior plus the NiMH battery needs to be heated to operational T.

Your mileage will suffer and the engine will run more in winter...unless you live in a climate where there is no real winter.

maximizese

So if I understand this correctly, one should do the ISC reset every time the 12V gets replaced? I bought my wife a used 2007 Rx400h with 83K miles on it from an out of state Jeep dealership. According to carfax.com, the dealership replaced the 12V battery, wiper blades, oil change, and tires (I even got them to change the windshield since there was a crack). I drove the car Az to Ca average 70mph and got an average 26mpg. Our stop and go city mileage has been about 22mpg and 75mph driving to Las Vegas nets 24mpg. The best mileage we see is when we're driving in slow-and-go congested traffic (5-30mph with no few stops) under this situation, we see 31mpg. I will try the ISC reset and hope for an improvement. This has been a little disappointing for me since I get 46mpg in my 01 Vw Golf TDI...I even get 28mpg when racing at the Buttonwillow track (4-cyl TDI has tiny fuel injectors).

mowmow

maximizese, you are already getting pretty decent MPG. The road condition also dictates the mpg, whether you are going up slope or down, or smooth 30-35mph on flat road where you can go full hybrid as long as the traction batteries allows you to before needing to recharge. The most i've got was on freeway doing about 55-60mph I get close to 30 mpg and a couple of times I have full traction battery charge up, after fueling up and reseting the trip computer, I was on full hybrid for a few blocks, I get up to 84 mpg then it drops down to regular high 30s then to high 20s. The RX is not a prius it doesn't get high MPG period and you can't really compare the RX to your Golf, so much in weight differences and gasoline electric VS diesel engine.
just my 2 cents

maximizese

I realize the Lexus Hybrid Drive System is more of a performance-based system as opposed to the Toyota Hybrid Synergy Drive System. The Lexus hybrid models outperform their gas-only counterparts and yield 10-40% better fuel economy. I also realize my Golf is not a fair comparison but after 10 years and 250K miles, you start to expect at least 600 miles per tank from your car. I'll go ahead and try the reset since my wife isn't getting nearly as good fuel economy as the other members here. Secondly, when I took the Rx for a test drive before I purchased it, the individual power window switches didn't work (indicating that the battery was changed and the Jeep dealership did not know how to reset the components including the ISC). Thank you for all the knowledge on this board...I never buy a car without reading the ins and outs.

valentin0

drive the 2007 Toyota Harrier - Rx350 , which is 3.3L V6 , which is the exact same model as the Lexus Rx400h, except it has smart key & push button start feature. Tried the ISC reset like this

1) making sure the right temperatures , etc etc,
2) Press the breaks, push start, then press the accelerator& brake together for approx 30sec,
3) Shut off the engine and place it in park
4) Wait 5 seconds.
5) Turn the ignition but pressing the brakes and push start
6) make sure the A/C and heater system controls are set to off
6) Lightly step on the accelerator pedal until the engine starts -then immediately take your foot off the accelerator and let the engine run until it stops by itself.

the engine ran for less then 30secs and stopped. so i guess it worked, lets see how it the mileage is.

garybuyit

Thanks for this info. I'm going to do this before my trip back home to Seattle from Chicago next week.
Garybuyit

1sWt2GS

iTrader: (6)

i found these gauges to never be that accurate anyways