As of today 6/14/22 I have recorded 21.9mpg!!! I've had this car for exactly 3 years and this is the highest fuel mileage that I have seen so far. I was running along at 65mph and 2500 rpms, that seems to be the sweet spot for these cars.

 

Suggestion for learning how to drive your RX for best mileage:

Set the dash for the real-time mpg readout, and calibrate your driving based on the readouts.

We all drive 80% of our miles to the same places, and the mpg readout helps know how best to maneuve.

 

So there’s a trick to squeezing a few extra mpg’s that I picked up driving cross country over the years. More recently I’ve put an engineering explanation to how it works.

It started when I noticed that I could beat cruise control over long distances, because cruise control tries to maintain speed, not mpgs. So going up hill while on cc, the car will drmand more fuel in response to increased load, and less fuel on the downside. However from an efficiency standpoint this is bad, for reasons involving the torque converter.

The torque converter sits between the crankshaft and the transmission. It’s a liquid-ring coupling that, by design, allows slippage between the rpm of the engine and the rpm of the shaft leading to the transmission. When load increases, so does slippage in the torque converter, and vice versa.

Here is a decent tutorial on the torque converter:

https://m.youtube.com/watch?v=WUFNySTjUmQ

So when a car in cc goes uphill, some of the increased fuel demand is wasted as slippage, and when going downhill not enough fuel is reduced to account for decreased slippage.

It’s not just over hills though. If you’re driving on flat terrain at an even speed, and then just barely increase pedal pressure, you will see increased engine rpm’s but speed won’t change. That’s because the marginal fuel increase is being wasted as slippage in the torque converter. The magnitude of the fuel increase has to be sufficient to overcome the slippage to induce a change of speed.

The difference isn’t small, about 10% of fuel economy in my experience. Meaning that if I drive the same route repeatedly, in cc I may get 22 mpg but manual controlling gets me 24.

So whether it’s trying gravity assist or simply driving at constant speed, you can increase mileage if you are aware of how small changes in pedal pressure are actually changing slippage in the torque converter, not driving speed.

 

My 2000 RX300 runs great after Knock Sensor change, MAF Change and IACV cleaned and Throttle Body bench cleaned.

There are NO Check Engine Lights

Yet it gives only about 18mpg in mixed CIty / Hwy driving.

What could be wrong? WHat should I check?

 

That's pretty much normal for me. Personally I think it's the gas. We are forced to buy an ethanol blend.

 

There's a whole thread about this in the stickies: https://www.clublexus.com/forums/rx-...out-yours.html

Mine is about the same. I consider it a V6 with V8 mileage.

 

Try and adjust style of driving seems a bit rich but probably what i would use to be first off at lights. So looks about right but how mello can you be.

 

I just finished a 9,000 mile trip with my 2001 289,000 mile RX 300. On the highway I got up to 23 MPG using non-ethanol gas, 20 MPG using ethanol gas and about 18 MPG mixed use in city and highway. So, your mileage sounds about correct.

 

The best I've gotten is 23 mpg on the highway. I usually average 20 mpg, but I idle a lot with the A/C on. I've used Top Tier premium fuel for the last 100K miles of my ownership. Make sure your tires are inflated correctly (30 psi cold).

 

30psi sound kind of low, no? I normally do 36psi

 

30 always sounds low to me also. Low tires get worse gas mileage and they run hotter.
I remember back when Ford recommended too low of tire pressure on their Explorers, and the tires were exploding and flipping them. Firestone got the blame for that for a while, until they figured out what was really the cause. Ford's fault completely.

I believe 34 up front and 32 in the rear would better serve me on these RX300s.( I have two). Of course, in snow, I would run them lower.

 

I remember when that happened, it was the Firestone Wilderness tires on the Explorer. I usually run 32-33 psi all around.
Wouldn't you want a little more psi in the rear tires when hauling something, or does that only apply for a truck?

 

If I was hauling/towing, yes. I don't have hitches on either of mine.

 

Do you put more psi in the front because of the weight of the engine? I have a hitch on the RX300 but I haven't towed anything really, I moved my Hobie Cat from one place to another once but that was less than a mile. I mainly use the RX as my daily driver and my commute to work is all interstate.
I have read somewhere that removing the roof rack bars helps with fuel mileage but is it really all that much. I am averaging around 21.5 mpg and that's it.

 

The weight of the engine, and the higher pressure makes it easier to steer and is less stress on the power steering components.