1998 Prizm, Only 21 mpg?

[Shawn5800]

Hey guys. I cant find any forums for the Prizm so i figured i would post here.

I just got rid of my Chevy Tahoe recently and bought a 1998 Prizm for my long commute to work. I expected to get atleast 30 highway. After going through 2 tanks. Im only getting 200-210 miles per tank. Whats wrong here?

My tank only holds 10.4 gallons. And i dont drive with my foot to the floor. I am almost driving all highway. My gas mileage should be much better for a 4 cylinder car....I would have kept my Tahoe if i knew it would be this bad.

I have done spark plugs, New 02 sensor bank 1 upstream, new air filter, Oil change. And thats pretty much it. New muffler to but that does not matter. What would be hindering my mpg that badly? The car does not hesitate at pickup nor does it drive like an aged car. It has great pickup and shifts beautiful.

Any ideas guys? Thanks alot. I appreciate any responses.

Heres the car anyways. Pretty well kept. Especially for $500 i paid for it. It has 100k on it.

[Shawn5800]

Bump, Please help.

[rgurleyjr]

So at 200-210 miles, your on empty? With all of your new parts, I'm not quite sure what to say. Do you get any black smoke out the tailpipe? That's pretty rich, I'm not sure if a malfunctioning fuel pressure regulator would cause bad gas mileage. Maybe your converter but you said your car runs great. Have you had your car checked for any DTC's?

[sestivers]

How are you calculating your MPG? You need to divide miles driven by the amount of fuel used, not the amount the tank holds. If you have been refilling at 1/4 tank and performing the calculation wrong you could be closer to 30 MPG. If you're driving close to 70 MPH in winter with the defroster on the whole time, that would be normal.

[randini667]

Sorry if I missed it, but what tranny?

-Rand

[Shawn5800]

It is a 3 speed automatic. And i fill up completely. Reset my trip meter. Then drive the full tank to as close to empty as "comfortable" Since im not sure if there is a gas light on these cars. Then i take the 210 miles and divide it by 10 gallons of gas i put into it.

21 mpg. ..I have yet to fill up completely after putting in a new air filter and doing the 02 sensor so. Maybe that will help.

[Crowbar911]

Have you checked tire pressure?
Are you using the front defroster? (it uses the AC compressor to get rid of the humidty, and will hurt gas milage)
Have you cleaned the inside of the car? The more your hold, the less your milage. (not the cause of that much milage loss)
Has your PCV valve been changed, or is it blocked?
Are you letting your car idle to warm up for a long time?

I think the 98's may have a MAP. in my 01, I replaced my MAF, and my gas milage skyrocketed.

Just some thoughts, hope this helps!

[randini667]

fueleconomy.gov reports a 1998 prizm 3 speed at 24 city, 30 highway. I'm sure you knew that.

I don't know what to say other than checking the basics: tire pressure, fuel sensor data, rich lean ratio, gas leak?

-Rand

[Skwyre7]

I'll echo what others have said. How fast are you driving? How is your tire pressure? Are you cranking the defrost? (The defroster lowers your FE the same amount on low as it does on high - the compressor is either on or off, the fan speed is different.)

[Shawn5800]

I drive like a granny around town, slow starts. No leadfoot for me. On my commute i usually stay at 70-75 mph. Wish i had cruise control Since i got the car the engine quieted down alot after normal tuneup and just driving it period. Tire pressure is good. Just bought 4 brand new winter tires. Defrost i was using for a while i will stop that now. Im at 140 miles now and just a hair below half a tank. So thats already an improvement. Ill see where i am after the 70 miles of driving tommorow.

Thanks for all your help guys. Appreciated.

[Skwyre7]

A 3-speed is going to suck FE-wise going 70-75 mph. There's no way around it. Third gear simply isn't tall enough to yield great FE. New tires take a good while to break in. Winter tires typically aren't great for FE either.

One other thing to try is to unhook the battery for a while to fully reset the ECM. Just like with PC's - if in doubt, reboot.

[DjiNN]

My corolla gets around 20MPG. believe me its not fun paying 30$ per week just to get around. Since my vehicle is suppose to get around 26MPG city and around 32highway. If i go on highways it still gets around 38MPG but on local roads I get 20mpg go figure ...

[Shawn5800]

Latest update. I got 250 miles out of a tank of mixed city/highway driving. Probably could have gone to 270 but didnt want to push it. I think thats my max ill get for this car honestly. Thanks for all your help guys. I appreciate it alot.

[Bhavesh]

changed from the Tahoe to a prizm for gas mileage? not what you expected, eh?

don't worry...I had a 4-cyl 4x4 Tacoma that got ~18-20mpg (as high as 24mpg highway) in the summer, then 15-17mpg in the winter, and switched to a corolla after mine got bought back, and I sort of miss my truck too

I'll give the corolla/prism some credit though: they're light, peppy, and ride relatively nicely compared to trucks though

but back to business:

don't forget this is winter time:
1.) cold air is dense air with more oxygen; and to ensure the proper air to fuel ratio is going into the engine, the car will add more gas to the increased oxygen
2.) gas companies will use additives to prevent the gas from freezing; it also lowers your gas mileage
3.) tire pressures (which looks like you already checked) lowers with colder temperatures; make sure you check that tire pressure cold and increase it to compensate for the cold weather if necessary. I brought all of mine up to 30psi and I raised my gas mileage up ~10%
4.) I'm not sure if you do this, but extended warm up times will slightly lower gas mileage
5.) snow tires, with their meaty tread pattern, can also reduce gas mileage compared to slick/smooth all-season tires

with that being said, I also live in MA with a 4-speed auto, and this winter am only seeing ~27mpg for mixed driving, and for a highway trip back from NY, only saw 33mpg. On the other hand I saw 38mpg on an highway trip last summer, so it just goes to show that winter time can reduce your mpg enough.

[FoxProGT]

Iv been wondering the same thing..... im a delivery driver and i monitor my gas mileage all the time....... the prizm should have close to a 13 -12 gal tank. if your topping your tank off at around 10 gal then you should have 2 or 3 gals hidden around that E ... XP

My mileage has really been all over the board... iv had 210 miles out of a tank and there has been times i can get 280. 1 thing i know for sure (for my case) is that driving highway will suck more gas then you think so i try to stay on the roads and since then, my mileage has gotten better.

i think these 3 speed auto prizms are better street cars then highway cars which is unique.

May i higher recommend that you keep a very close eye on your oil levels since your on the highway doing 70 so much.