I have a 99 GS 10th anniversary edition with an auto, I'm running 225/50/16 tires. in the past few months my mileage has gone from 26-28 down to 22-24, used to i would get close to 30 on the freeway now i'm only getting 26.7 completely freeway only going 65. anyone know why this could be or how to fix it. She's only got 125k miles and the mileage change was pretty sudden. I'm thinking it might be from 2 different reasons.
1. I, being stupid, put lucas engine **** in my oil...
2. Tranny fluid could be in need of change?

Only mod is a CAI and the mileage was sucking before i put it on and hasnt changed from it. Sparkplugs are recent NGK V-power. I got new wires too. Air filter is clean and pretty new.

If it is cuz that Lucas stuff anyone know how to get it out, been 2 or 3 oil changes since i put it in.
Could the 225/50/16 tires make much difference over 205/55/16 ???

Fuel filter its like $20

oh, replaced that a few thousand miles ago.
would 225 over 205 tires make that much dif?

oh, what is typical mileage for a 2g GS with auto tranny?

I have no idea if the tire width would do that.

it is possible that ithe width does that. The wider the tire, the more rubber; the more rubber, the more weight; the more weight, the harder it is to move the weight.

If it's harder to get the car moving, it is going to take more gas to get it to move, then there is your problem. However, you would have noticed that change after you put the tires on...

What did you install or fix immediately before you began to have this problem?

Could be as simple as tire pressure.

could also be where you get your gas. have you been fueling up at a different place?

Eric you will relate to this more than other people because we aren't too far apart. But I notice that when I fuel up at sunoco (this is in my sable DD) I get about 340 miles per tank and about 25 mpg. When I fuel up at Turkey Hill I get about 420 miles per tank and 30mpg. HUGE difference.

I stick to getting my gas in Jersey its cheaper. But when I was driving out to Lebanon Valley/Hershey every weekend I would either get Turkey Hill or Hess .. depending on whether I took 80 - 78 or 422 to 222 home.

But honestly I haven't paid enough attention to my MPG lately I usually fill then add 20 then fill but my driving is soooo freaking sparatic its hard to tell.

Im sticking with tire pressure untill this is proven to be correct.

Yeah, you can't really go by what it says on the inside of the door. I usually go 32-34 psi on the front and 30-32 psi on the rear. most tires can handle like 36 and it usually says so on the tire.

scope the upstream o2 sensor.

There's more rotational mass, plus there's also more road friction -- both will impact gas mileage. That's a big reason I decided to stick with 205/55x16 on my Scion -- of course, if your wider rim is super light (not typical), then you may break even or better on rotational mass :)!

i just went to 215/40 they do good, but seriously tire width shouldn't make that big a difference....

what i did immediately before the mileage drop was the lucas engine stuff. i'm not sure how to get it out. Upstream O2 sensor, i'll have to check that out. I'm doing some work on it next month / headgasket, timing belt etc...

I always run a little more pressure than what the door says, i've changed it and not really any difference. I'm thinking that lucas junk, but really it seems a little too low for me. I fill up at several different places, Shell, Arco, Chevron, Beacon, whatever and the mileage doesnt change based on those.

Lucas and every other engine addative is JUNK!!!

I realize that, now how do i get that **** out?

change your oil. run it for 100-200 miles change it again.

it is possible that the lucas oil is doing it because that stuff is really thick and sticky. It might be restricting the rotating assembly because of that. Its like adding a 20lb weight to your crank pulley or flywheel