I have a 2012 xB. I never paid much attention to my fuel mileage until recently when, due to the pandemic, I am no longer doing most of my driving on California freeways. These days I am driving no more than
50 miles per week, all of which is city driving--going to and from local stores, church, and other short trips. I love the nifty gauge that continually shows how many MPG I am getting as a drive around on city streets.
It will show anywhere from 5 miles per gallon up to 90 miles per gallon. I put 7 gallons of gas in the car last week and set my trip odometer to 0. When the low fuel light came on, I was shocked beyond words to see
that I had only driven 60 miles. This means that I was getting about 8 miles per gallon! I kid you not. 8 miles per gallon.

I put in 8 gallons at my gas station on the next block. I set my odometer to 0 again. And i began using a technique I haven't used in years. From a complete stop, I will accelerate up to 30 MPH, put the car in Neutral and let her coast along the streets of Oakland until I come to a
stop sign or red light or get behind very slow driver. My MPG indicator will show that I am averaging 90 MPG. There are many streets in Oakland on which I can cruise along in neutral for blocks. Needless to say, my gas mileage has improved immensely. I have gone 120 miles
since I put the 8 gallons in about 10 days ago and the low fuel light has not yet come on.

If I make it to 200 miles on those 8 gallons, I will be very happy.


*Moved to Correct Forum by Administrator

Sticky Where to Post Your Question

Sticky How To Advanced Search SL (Scion Life)

______________________________

 

Coasting with the engine running is not good for your catalytic converter(s). This is why Toyota recommends warming the engine while driving, not while parked.

Electronic fuel indicators are cool but they're not effective at gauging fuel consumption. What you want is an average mile-per-gallon, not one extreme either way. The best way to get your average mpg:

1) Fill fuel tank to the top. No, not at the cap threads but at the first auto shut-off, plus one goose. Only one. (This will fill your tank without getting liquid gas in your fuel vapor recovery system.)

2) Drive as you always drive. You don't necessarily want grandma's average mpg, you want your average mpg. (Consider refilling at or around one-quarter tank of fuel or more. Fuel cools and lubricates your electric fuel pump. Too little fuel will shorten it's life.)

3) Fill fuel tank as described in step 1. Divide the number of miles you drove by the number of gallons that refilled your tank.

For example:
Miles driven - 305.2
Gallons of fuel to refill tank - 17.496

305.2 / 17.496 = 17.4 miles per gallon.

 

These gauges have been around for decades. They're just vacuum gauges with scale written as MPG. Shows theoretical instantaneous MPG, not really useful because you need to take average of all readings over time (integrate with respect to time for those who know calculus).

Anyway, best way to arrive at MPG is show above. Record numbers of miles driven and divide by gallons used to arrive at miles per gallon.

 

And your results will vary, even when you repeat the steps carefully. This is because you'll rarely, if ever drive the same combination of highway and city miles. Spirited versus non-spirited driving will also vary.

 

Keep in mind that the low fuel light comes on at a quarter tank on the xB. You were no where near empty when it came on.
The light is designed to come on so you have plenty of time to find a gas station even if you are in the middle of nowhere.

__________________

 

Do you have a source on either of these? From what I've read, coasting is not recommended because it's considered less safe (no ability to accelerate if needed while in neutral), and it gives worse mileage than simply taking your foot off the gas. I don't know of any reason it should affect your catalytic converter. And warming while driving is also just more efficient, and safe as long as you don't accelerate quickly until after it's warm.

Pretty sure these days the computer just calculates it based on the speed and fuel injector signals. That's the only way it's going to be able to calculate an average MPG over time.

OP may want to try a fuel logging app to get a long-term accurate picture of his fuel economy.

<CSB> I once had an '83 Plymouth Colt that suddenly started getting terrible mileage. I couldn't explain it until I looked under the hood with the engine running and saw that the fuel pump had sprung a leak and was squirting gas on the exhaust manifold. I'm amazed the thing hadn't already gone up in flames. </CSB>

 

"Heat can be damaging to almost any engine component, so it’s no surprise that it’s one of the most common causes of catalytic converter failure. Engine exhaust is already quite hot, so when you add in a contaminant like unburned fuel, which can find its way into the exhaust system when your motor is running too rich, you compound the effect, as that fuel typically ends up burning inside the converter itself. This can damage or even melt the honeycomb structure that is required for the catalyst metals to do their job, leading to a blockage and restriction in exhaust flow. If your engine is misfiring or if you see a warning code for a bad oxygen sensor, it’s a good idea to take care of the problem before it can lead to catalytic converter failure."

"Running too rich" might be a symptom of idling and or coasting too much.

Catalytic Converter Failure: 3 Common Causes (napaonline.com)

 

Don't know if I'd trust an outfit whose primary purpose is to make money off you selling defective and countrefeit parts. Ceramic substrates on modern catalytics can't melt. But they can get clogged, or coated, lowering their effectiveness.

ECU actually shuts off fuel when you coast in gear. This is plot of data from TechEdge wideband O2-sensor. One of best units on market, fully digital with datalogging.


time = 5773, I approach hill and increase throttle lots to maintain speed (TPS=green)
5800 - torque-converter lock-up clutch disengages and RPMs increase (blue)
5900 - ECU downshifts to 3rd-gear, goes into open-loop rich mode and ignores O2-sensor, AFR = ~13.0:1
5950 - I let off throttle slightly to maintain speed up hill, ECU shifts into 4th-gear, leaves lock-up clutch disengaged
5950-6215 - note I gradually increase throttle on uphill to maintain speed
6215 - near top of hill, increased throttle results in ECU downshifting to 3rd for little bit
6275 - as I crest top of hill, I let off throttle slightly and ECU upshifts to 4th and engages lock-up clutch
6400 - with lower load, lower-throttle after crest of hill, ECU resumes closed-loop O2-sensor operation
6450-6493 - I let off throttle completely to coast down hill, ECU shuts off fuel, AFR = 380.98:1, pretty much zero fuel
6493-6700 - I give it enough throttle to maintain speed at bottom of hill, ECU resumes close-loop O2-sensor operation

I could've put it in neutral in 6450-6493 timeframe and have engine at idle. In which case, it would've resulted in AFR=14.7:1 most optimum mixture. Not sure how that would hurt catalytic either.

With strict emissions standards nowadays, it's practically impossible to "run too rich" for any significant amount of time. Even WOT uses about 12.5:1 AFR, much leaner than previous settings of 10.0:1 from '80-90s.

Only time you'll get constant "too rich" mixtures is if you've got failing O2-sensor. It'll put out lower-than-normal voltages and trick ECU into thinking mixtures are leaner than actual. ECU will inject additional petrol trying to compensate. This might be why OP's getting poor mileage? Although using that gauge in instantaneous mode is deceiving, should use average mode.