VegasRX300

Just got back from my daughter's graduation. From Las Vegas, NV. to Jackson, WY. and back. Little over 1400 miles round trip.
Speed limit on I-15 in Utah is 80 MPH, so I go 85 MPH. I like it cool so I have the air on.
The best I got was 25.6 MPG. Worst was 18.5 MPG. It averaged out to be 23.8 MPG for the trip. This is with the air on.
Even when the speed limit was 65 MPH on rural roads I like to drive 70-75 MPH.
I didn't go by the cars read out. It was always higher. I went by the miles I drove and the amount of fuel the tank would hold. And I always topped it off until it couldn't hold anymore fuel.
I have changed everything to Mobil 1 synthetic, engine, trans, rear end, transfer case. I think this helps with the overall MPG.
The 1999 RX 300 ran flawlessly and turned 179,000 on the trip.

hypervish

Nice! I'm usually getting around 20-21 mpg at those speeds since most of my driving involves uphill grades many which are quite steep. However, I see around the same mpg when driving around Illinois (flat roads)when I go on road trips.

What tires are you running?

My MPG dropped nearly 10% with new tires, and I know I can't attribute all of that to the new tread as the old tires weren't quite worn. Other factors such as tire compound, psi,etc. all play a role.

VegasRX300

The tires were new and on the car when I bought the car last year. A brand I never heard of before but I looked them up and they were $107 each then (Discount Tires has them on sale now for $77.08). Not Michelin priced.
Made in China, a brand called Jinyu. Ys71...225/70r16, 103T.

I also drove from Las Vegas's altitude of 2181' through Evanston, Wy. of 6749' altitude to Jackson, Wy. of about 6250'. And one mountain pass between Evanston & Jackson, Salt Creek Pass at 7630'

I really expected a lot worse MPG because I am not known to drive very slow. I just want to get where I'm going
Think it was 1974 I made the trip from Jackson, Wy. to Las Vegas (about 700 miles) with a passenger in my Porsche in 8 1/2 hours...and we had stopped to eat too. Now that was flying low.

matts6887

WOW!; that is great mileage for a 99 300! sounds like you must be doing something right! I wish i could get that kinda mileage with mine! but i think with mine the best Ive done is like around 21mpg but that was just like a few times here and there. Very cool!

Bobster999

Last time i checked mine was 22.4 mpg driving about 65 mph.

matts6887

That too is pretty good bob!. There are so many variables that can determine what kinda mileage one will get that its too many to list. But whatever you guys are doing to get that kinda mileage u are doing something right!

mckellyb

It's amazing what a very steady throttle and speed can do.

My wife followed me, I was driving the motorcoach, from Vegas to west of Denver. She managed 31.something on not one, but two tanks, so I know it wasn't a fluke on fill-ups.

The coach had developed a flaky oil-pressure sending unit which eventually cuts power to protect the engine, hence my top speed was about 60 MPH some of the time. Also, it's a very slow, but continuous, climb, for parts of that trip.

One time she asked me over the radio, because we'd slowed to about 45 MPH, "is the sender acting up, again?"

Me: "No, Sweetie, you'd be surprised, but we've been going uphill for the last ten minutes, this is just it."

GPS verified the slow elevation increase, and 275 HP/660 torques motivates 28K lbs. only so well (I was pulling our 'toad' (towed car) too).

The RX300 can get amazing MPGs under the right conditions.