Thread: Bad Gas Mileage!? Help

DONT flush your tranny. Just do a pan drop and filter change, unless there are papers documenting that it has been flushed every 30k-50k miles. Flushing it will remove all the old fluid and on older trannys sometimes the clutch material in the fluid is what is helping the tranny to still work.

As far as your gas mileage do the tune up you have planned. Also get some fuel injector cleaner. If you want the best results use Chevron Techron fuel injector cleaner or go to the dealer and get theirs. They're both the same thing but the Chevron is only 12 dollars and the dealers is like 25 to 30.

Also check your RPM on the highway to make sure the car is getting into 4th. If the 4th clutch hub hasn't been replaced yet and there is 220k on the car I would be amazed if you have 4th. If your seeing about 3000 RPM @ 65mph then you are missing 4th

where do you live? winter gas will lower MPG. Ethanol blends lower MPG. lots of other little things can lower mileage such as tire pressure.

Replace both o2 sensors if original, after 220k they arent very good anymore. Heck after 100-120k they should be replaced.

Even on winter gas I still managed 28-30mpg this winter on the highway.

I have a stock GT that was getting that, and I replaced my thermostat and now it does much better. But like it was said up there, my engine wasn't getting to operating temperature and it caused more fuel to be used.

Prolly the issue.

But cruising at 3,000 rpm at 75 seems kinda high, like way high. At 70 mph in 4th gear with 2.93's (GTP gears) you should only be at 1900-2000 rpm, at 75 mph maybe 2200-2300. At 3,000 you'd still be 3rd gear going that fast, and that means your 4th gear is gone. I'd do a full rebuild at this point, everything inside the tranny is worn out.

get the stock 190 one you dont need the 180 t stat

I know when I am going 80, I'm at 2,900-3,000 RPMs, but then again the GT could be geared different. And my car shifts into all gears so I think it's just my gearing ratios lol

that seems like high rpm's. next time out. pop the shiftier into 3 rd from over drove and see if the rpm's rise, if they dont your no longer have OD.

if it wont move in D at all, free revving deal, thats the forward band that broke. it will need a rebuild. or find a cheap used tranny.

its a crap shoot how long it will last. maybe yes, maybe no. flip a coin lol

with any luck you'll make it 30 days. i'd be more then babying it too.


thats not to bad of a price, make sure that comes with a new TC. you never want to reuse them.

seems like you had no over drive, 3,000 rpm at 80 mph is to high. so you were drinking gas on the highway. and now its seems like the forward band is broken.

I was getting around 19 and for the past 2 months have been following this mantra - Nowadays I always fill 93 octane at a Shell station, I add about 10 oz of Lucas fuel injector cleaner with every tank.
Now I consistently get around 28 with minimal stop and gos.
If AC is turned on > 30% of the time it drops to 23.
Also you might want to check your thermostat, i read that if you use 180F it burns more.

The 93 is 40c costlier but if you do the math.
14g@3.79 = 53.06$ = 392 Miles
14g@3.39 = 47.46$ ~ 300 miles

So for ~6$ more I get 92 more miles, i.e. 4.6gallons of 87 octane which would have costed 15$ more.
Try it and see.