What exactly causes MPG to decrease as the car gets older?

[ShawnD1]

40 psi on the tires? Read the sticker on the door. I am sure it tells you to do less than that...although mine is the 2.3L with 17inch money wasters.

Depends on the type and size of tire. Higher performance tires will have higher pressure ratings. That and I think my spare tire is something like 65 psi but the regular tires are 32/30 psi. I think the door sticker only applies to the stock tires, but I'm not too sure.

Also, if this is the big 2.3L, how did you get that mileage with an auto? I have taken straight highways trips for 400 miles and I had to refill before I got there.

Are you using stock tires? Changing the tires can radically change the gas mileage. Big grippy expensive tires are usually bad for gas mileage because they're built for performance.

 

[BlahBlahYouToo]

Seafoam does contain Naphtha so thats why it cleaned some build up, but in the fuel that's really the only ingredient that has cleaning power. While for example redline has PEA and Naphtha.

i put seafoam in the crankcase and the brake booster, techron in the gas tank.

i like to believe all black smoke coming out of the exhaust is buildup of some sort that's robbing me from power and mileage.
regardless of what it's doing, or not doing, it's still cool as hell to watch and leaves me feeling like i cleaned up something.
the same feeling you get when you open up your pc case, and blow a can of compressed air into it, and clean the dust off the fan blades.

 

[Zenmervolt]

Depends on the type and size of tire. Higher performance tires will have higher pressure ratings. That and I think my spare tire is something like 65 psi but the regular tires are 32/30 psi. I think the door sticker only applies to the stock tires, but I'm not too sure.

The sidewall rating is nothing more or less than the maximum cold inflation pressure that the tire can safely withstand. You do not want to blindly inflate tires to sidewall pressures.

The recommended pressures in the owner's manual or vehicle sticker are valid for all tires, regardless of whether they're the stock tires or not, as long as you keep the same size. If you're looking for specific handling characteristics, the right thing to do is start at the pressure listed in the manual and then make adjustments from there (up to the sidewall maximum) based on how the car responds to the changes and how the wear pattern on the tires looks.

Are you using stock tires? Changing the tires can radically change the gas mileage. Big grippy expensive tires are usually bad for gas mileage because they're built for performance.

Yeah, you'll maybe lose a whole 2%-3% of your gas mileage by going from the lowest rolling resistance tires to the grippiest tires on the market. That's not at all within the margin of error for the vast majority of drivers. 🙄

Unless you're going all-out for every last bit of fuel economy (e.g. Prius, Insight, Volt, etc) big, grippy tires just don't affect fuel economy enough to worry about. Whoever told you that tires can "radically change the gas mileage" was full of shit.

ZV

 

[Vic Vega]

None of my cars have lost MPG as they have aged.

Follow the service schedule in your owner's handbook. It's in there for a reason.

 

[JCH13]

Check the tires' condition.
Run some SeaFoam through the intake/fuel/oil sump.

IIRC the MZ3 has some pretty aggressive cold-weather enrichments, so you would expect a drop in fuel economy as the weather simply gets colder.

Your WB O2 system might be acting up a little bit, that might be worth investigating.

 

[JEDI]

Check the tires' condition.
Run some SeaFoam through the intake/fuel/oil sump.

IIRC the MZ3 has some pretty aggressive cold-weather enrichments, so you would expect a drop in fuel economy as the weather simply gets colder.

Your WB O2 system might be acting up a little bit, that might be worth investigating.

whats a 'wb 02 system?'

 

[JCH13]

Sorry, wide-band oxygen sensor and associated wiring. The sensor can get fouled up, especially with how rich Mazda engines run some times. They love their cold-start enrichments.

 

[JEDI]

Sorry, wide-band oxygen sensor and associated wiring. The sensor can get fouled up, especially with how rich Mazda engines run some times. They love their cold-start enrichments.

Where is it located, and how would I fix that?

 

[JCH13]

Where is it located, and how would I fix that?

It's a little sensor probably threaded into a bung that's welded somewhere on your exhaust manifold. There might be two, one before the catalytic converter and one after. Checking it would be a "swap and pray" technique.

You may want to post your question on Mazdas247.com too. There is a lot of 3 support there.