what could be the reason of my 99 Camry V6's low mpg?

[fengleim]

I have been watching the mpg of my 1999 camry xle v6. I am commuting from home to school, 2-3 mile one way, I occasionally go shopping for around 10 miles road trip.
Today I filled the gas tank and did a calculation, found out my mpg is only 14.6 mpg ( #87 gas). Is that outrageous?

I can not feel anything like misfiring ( I should feel engine choking / shaking in such case,righ? ). I cleaned the air intake side of the throttle body with carb cleaner. I keep using mobile 1 synthetic oil and decent filter. I drained and filled the tranny fluid with Castrol IMV fluid twice already.

It is not burning oil, no leaking. brake is fine and is not dragging. ( per the oil guy)
one of my O2 sensor went bad last year and I had it changed with a denso.
my tires are about 2 years old.

so far my car feels really good, quiet and agile. But the mpg is low- local mpg is always around 15-16, now even lower to 14 in this wonderful season. what could cause that?
I am thinking about using seafoam to do a vaccum line feeding. will that help? or should I change the spark plug ? ( that is quite some work for v6)
Please enlighten a novice.any suggestion is appreciated.

[fenixus]

I am getting around the same in short distance city driving from Mon-Fri and occasional longer trips. anywhere between 14-17MPG.
highway driving was giving me 26-27 MPG.

however I discovered recently I had bad spark plugs (from running rich in past for a long time) and I had both PCV hoses cracked on ends, possibly allowing some slight vacuum leak...

I would check/replace the plugs first and go from there. you can do the whole minor tune up if you like.

other than that, jack the car up and check the wheels free spin (trans in Neutral for fronts), you could have bad wheel bearing or a dragging caliper somewhere. even set too tight parking brake will cause some ill effects on MPG.

also check if your tires are inflated properly (32psi at cold tire) and if wheel alignment is OK.

ask me in 2 weeks if my MPG got improved with new plugs, I will be taking the car for a road trip, 700 miles each way soon.

if you do decide to sea foam the engine (it's quite easy and safe), remember to do it BEFORE you change the spark plugs. sea foaming engine releases so much carbon that it can damage the spark plugs (or at least make the run worse). for o2/AFR sensors it doesn't matter much, they sit in the exhaust anyways.

it could be wise to replace the other 2 o2 sensors (second upstream and a downstream under car) too.

Originally Posted by fengleim

I have been watching the mpg of my 1999 camry xle v6. I am commuting from home to school, 2-3 mile one way, I occasionally go shopping for around 10 miles road trip.
Today I filled the gas tank and did a calculation, found out my mpg is only 14.6 mpg ( #87 gas). Is that outrageous?

I can not feel anything like misfiring ( I should feel engine choking / shaking in such case,righ? ). I cleaned the air intake side of the throttle body with carb cleaner. I keep using mobile 1 synthetic oil and decent filter. I drained and filled the tranny fluid with Castrol IMV fluid twice already.

It is not burning oil, no leaking. brake is fine and is not dragging. ( per the oil guy)
one of my O2 sensor went bad last year and I had it changed with a denso.
my tires are about 2 years old.

so far my car feels really good, quiet and agile. But the mpg is low- local mpg is always around 15-16, now even lower to 14 in this wonderful season. what could cause that?
I am thinking about using seafoam to do a vaccum line feeding. will that help? or should I change the spark plug ? ( that is quite some work for v6)
Please enlighten a novice.any suggestion is appreciated.