Low MPG

I have an '02 with 148K miles and am getting about the same mileage as you report. This is about normal for the kind of driving I do: short trips around town, little highway driving, and winter temps all mitigate against higher mileage in an 18-year-old car! On more extended trips at 50-55 mph I can nudge the mileage up to around 40. You might check the condition of your 12V battery; I doubt that it has much if any bearing on mileage, though. BTW, the battery hold-down belongs under the shield, not over it, which is why yours is cracked. You have an undersized (after-market) battery; when you replace this one, get a battery with a 51R case. I converted the terminal clamps to SAE and installed an Interstate battery. As for the blanked spaces on the dash, I've wondered about that myself. AFAIK the original Classic came with few options (cruise control, CD player), so there would seem to be no reason to have extra buttons in those places. But who knows, maybe Toyota was thinking of future possibilities (which never happened with this model).

 

Your panel is stock like mine, blanks there for future diy additions.
Your mileage is normal ie low for a 19 yr old.
Replacing all cells with gen 2 modules or all new gen1 modules might raise it by 8 but expensive.
Cleaning the EGR and intake may raise it by 5, new spark plugs maybe 3
Check that all wheels spin freely, or caliper may be stuck, bearings worn

 

Clean your battery posts from corrosion.
Buy Techstream or Dr Prius app to check HV battery health

 

do you know the maintenance history?

how are you measuring mpg's?

 

The biggest variable in MPGs is often the nut behind the wheel. Drive like there's a raw egg between your foot and the gas pedal. Control speed as much as possible with the gas pedal rather than the brakes, paying as much attention to what is way ahead of you as to what is right in front of you.

Make sure that your tire pressures are correct, and perhaps have the alignment checked.

Check all basic maintenance items, especially spark plugs.

You will get lower mileage in the winter.

But yes, an old, on the edge HV battery will not help matters. If you've been driving for a while and the car is all the way warmed up, and you come to a stop, how long does it take for the gas engine to shut down? There are techie gadgets you can get to check out your HV battery. Search the forum for Techstream and the Dr. Prius app.

 

If you're in LA, that's low. If you're around Tahoe, or otherwise where it snows and gets cold in the winter (like if "ca" is really Canada), that might not be too far off.

My '01, with 229,000+ miles, has a lifetime average of 44.3 mpg. It always gets better mileage in the summer and worse in the winter. Over the past couple of years, on a 5-tank moving average, I've seen it be as low as 43 at about this time of year, and as high as 46 in July and August.

You can check the stuff that's made engines run poorly since Bertha Benz's joyride. You just can't use a hairpin to clean out the carburetor anymore.

Engine air filter? I use the Toyota ones, but even an aftermarket new filter is better than a dirty one.

Mass airflow sensor clean? It lives in the bottom of the air filter housing - right above where the plastic housing clamps on to the metal throttle body. You can take it out of the housing (those two Phillips-head screws that you see, right on the front (FRONT) of it) and clean it yourself, but carefully. The easiest way for n00bs is to use the spray can of cleaner for it at the auto parts store.

Is the air filter housing clamped down tight on the throttle body? If it's real loose, the engine won't run, but if it's a little bit loose, the engine can suck air that the mass airflow sensor doesn't know about. I found this out the hard way in traffic one day about 15 years ago. I'm not sure whether it was me, or a shop, that didn't tighten it, but the clamp bolt was loose; reseating the housing and tightening the bolt fixed it.

Spark plugs? Gen1s used iridium spark plugs from the factory. I pulled them out a couple of times before 100,000 miles, believing there was no way spark plugs would last that long... and they were fine. I ran the factory set until about 137,000 miles, and then put in the iridium replacements that NGK makes (IFR5T11 or 4996), and that set is still in there.

I think that when Gen1s were brand new, the only source for the plugs was Toyota - the aftermarket didn't have them until a couple of years later. So it's possible that somebody put random plugs in it at some point, maybe because they thought the right plugs weren't available, or they balked at the price of the right ones - currently about $30 online for a set of four from NGK.

If you do get new plugs, I recommend using a little anti-seize grease on the threads, just because they will usually be in the engine for so long. Don't get any grease on the sparking end, or the end where the ignition coil connects - just on the threads. The car parts store has a small tube of the right grease for a few bucks.

Oil? You can't tell by looking whether you have 5w30 or 20w50. You can probably tell if somebody put 90w gear oil in there, by the smell if nothing else. The Gen1 calls for 5w30, and heavier oil will affect the MPG a little bit. This is pretty simple to fix; do an oil and filter change and make sure 5w30 goes back in. I personally run dinosaur juice; other people like synthetic. I don't think Toyota required synthetic oil until about Gen3 (late 2000s models).

What size tires are on it? Stock is P175/65R14. If it has the stock wheels, the 14 is probably the same, but someone may have put slightly different tires on it (the other two numbers). Different tires will have slightly different diameters, which makes the speedometer and odometer be off by a little bit. Usually this is just a few percent, though. A good way to test this is with a real GPS reciever (not a cell-tower-triangulating fakeGPS in your phone); drive the car at a steady 65 mph on the highway and see what the GPS thinks your speed is.

Fuel? If you're running E85 (kind of hard to get in CAlifornia, might be more common in the CAnadian prairies), or even E10 (which is really about E15 or E20), try a couple of tanks of gas without any bourbon in it. It takes a little while for the engine computer to retune, which is why it takes a tank or two to see results.

As others have said, tire pressure? It takes different pressures front and rear. There's a sticker either on the driver's door jamb or in the glove box that tells you the right pressure. Never trust the tire store, the quick-loob place, or the stealership to do this correctly on this car, or any other car... they will always inflate all the tires to what it says on the side of the tire, which usually is nothing close to what the car actually calls for.

The original 12 V battery in a Gen1 was a weird size for North America at the time. Toyota sells (sold?) a kit with a different tray, hold-down clamp, and cables, that would let you install a larger battery that you actually can get. Some people have installed aftermarket AGM batteries, like Optima or Odyssey, instead.

They did, but nothing in the US that I know of used those blank switch spots near the power mirror switch. As far as I recall, they all came with AM/FM/cassette as standard. The floor mats might have also been an option, but every Gen1 I've seen has them. Options were a single-CD player (which goes underneath the HVAC controls - if you don't have that, I think you have a plastic pocket there), a CD changer (not sure where that lived, possibly in the dash as well), navigation (ECU under the passenger seat, plus a GPS antenna somewhere else). Both of the CD options and the navigation were operated through the existing touch screen and buttons around the touch screen.

I think those empty switch plates were for options in other countries. Some countries have or had laws about leaving the parking lights on when you were parked on the city streets at night; some of them required things like headlamp cleaners (either tiny wipers or washer-fluid squirters or both), that are often implemented with extra switches. It may have also been Toyota corporate policy to always have a couple of blank switch plates in every car, even if they didn't have anything to put there at launch.

 

Your Imgur links weren't loading last night, and today they are. Yes, that is definitely a replacement (and wrong) 12 volt battery.

At some point, someone did install the kit from Toyota that gives you SAE-sized battery terminal clamps. The original 12 volt battery had JIS-sized posts, which are much skinnier than the common US ones; some mechanics call them "pencil posts". The kit had a new positive terminal to bolt onto the existing fuse box, and a new negative cable, both of which you appear to have.

The fragment of the address visible on the label points to "David Alfaro Siquieros" street on the south edge of Monterrey, Mexico. There is a Johnson Controls facility at this address, and they make several brands of car batteries. (Interestingly, there's also a Toyota dealer right around the corner, but its address is on the cross street. I also think it's just a dealer and not a parts warehouse, but I could be wrong.)

The reason that battery is wrong is that it's a flooded battery - it has liquid electrolyte in it, sloshing around between the lead plates. Most car batteries that go under the hood of a car are like this; they're cheap to make and last a reasonably long time. However, they can potentially (ha!) outgas hydrogen when charged. Under the hood this isn't such a big deal, because the hydrogen will usually float up and out of the engine compartment. However, in a trunk, which shares an air space with the passenger compartment, you don't want it.

The original Toyota battery, and most of the replacement batteries, are "absorbed glass mat" or "AGM" batteries. This means that there are sheets of (I think) fiberglass stuffed in between the lead plates, and the electrolyte is soaked into the fiberglass... there isn't any loose liquid electrolyte sloshing around. In theory, if charged correctly, an AGM battery won't make hydrogen. In case it does, though, the Toyota batteries have a hole in the top, which connects to a tube that goes down through the floor of the battery compartment, to dump any unwanted gases outside the car. (Motorcycle batteries have a similar setup, if you've ever changed one of those.) Your battery most likely doesn't have the connection for the tube.

This battery is probably not the cause of your low MPG, unless it's really worn out. If it is, the gas engine will run more than usual to try to keep the 12 V battery charged up. You can take it out of the car and have it load-tested like any other car starting battery at the car parts store; I would test it off the car, and not let them use the tester they carry out to your car on it. (If the kid with the on-car battery tester screws up on a Corolla, they pop a $5 fuse or a $100 alternator. If they screw up on a Prius, they pop a $5 fuse or a $500-$1000 inverter assembly.)

You mentioned 12.5 V "on the meter" - is that with a voltmeter/multimeter on the battery terminals in the trunk? Around 12.6 V should be correct for a fully-charged flooded battery with no load. If you go up and start the car (READY light on), the voltage at the 12 volt battery terminals should go up; the times I've checked mine, with a good 12 V battery, the meter has read something between 13.8 and 14.0 V. This is with the car READY, but the headlights, radio, heater, etc all switched off. If it's way lower than that, your inverter/converter might be struggling to charge your 12 V battery, which usually means the 12 V battery is on its way out. Again, having the 12 V battery tested, off the car, is how you find out.

I hope this helps!