Thread: bad gas mileage and trans temps high

had this in another thread but i figured i would start one just for the issue

anyway 04 GP gtp comp G with 113k miles it gets pretty sad mpgs even though i drive about 80% highway at 70mph and at that speed while not beating on it the trans temps get as high as 225 * consistently i would say 90% of the time that the transmission is warmed up it is over 200*
i just cant figure out the issue, its about to get headers, new o2 sensors and a highflow cat and i hope that helps

so far i have replaced
plugs (factory replacements) and wires (bosch lifetime warranty)
changed supercharger oil
k&n cone filter
transmission filter and fluid (merc 3?)
fuel filter
took the throttle body off and cleaned it to the point of being almost spotless
cleaned the mass air flow sensor with electronic parts cleaner
tires are about 5k old with 35ish psi
if it matters the car says the alternator is charging well (between 13.8-14.5 volts)
coolant is still dexcool but still looks bright orange/red
car no engine lights on

thinking speed daddy

Tranny coolant temps are susually around 200 range easily. On these hot days I get around 215 or so. If im correcnt I head somewhere around here above 220* is when you need to worry.

And what do you mean by crappy MPGs?? cause i drive alot of highway and my average (as calculated by DIC) is still onle 22ish because of how I drive in the city.

Nothing you have done or seem to be planning are going to change transmission temps.

The trans temp is related to clutch slipping and the amount of cooling that the super small cooler in the side of the 180-195F radiator provides. Not sure where you get the idea that modding will help trans temps, you may want to consider an aftermarket cooler.

Originally Posted by BillBoost37

Nothing you have done or seem to be planning are going to change transmission temps.

The trans temp is related to clutch slipping and the amount of cooling that the super small cooler in the side of the 180-195F radiator provides. Not sure where you get the idea that modding will help trans temps, you may want to consider an aftermarket cooler.

i figured changing the fluid and filter would help, the rest of it was to rule out issues for the lesser then expected mpgs

Originally Posted by tayl5645

Tranny coolant temps are susually around 200 range easily. On these hot days I get around 215 or so. If im correcnt I head somewhere around here above 220* is when you need to worry.

And what do you mean by crappy MPGs?? cause i drive alot of highway and my average (as calculated by DIC) is still onle 22ish because of how I drive in the city.

well when i went to Florida, i got 22mpgs with the a/c off and the cruse on around 70mph and i didnt get much better on the way back, right now without really beating on it my average says 19.6mpg, i understand its gonna go down if i beat on it but it seams it stays around there wither i bet it or not

what i am getting at is people on here say these cars can get 30mpg on straight highway and i am getting 22mpgs, dont get me wrong i understand its a full size car but i feel theres something wrong

I mainly get 25s no where near 30s wish I did. Also the older it get the less likely you are to get the fresh MPGs.

Originally Posted by Iceman6669

Mine is a 97.. granted series 2 not 3. But I can get 24-27 everyday driving.. And that is with me driving it like i stole it. Pure highway I can break 30. I got a buddy who has one... Drives like a grandpa.. And he gets 30+ everyday driving...

Are we speaking SE GT or GTP... each one is gonne be completely different I would think it would be pretty hard to muster 30+ on the supercharged with regular driving

is it the gtp's or the gtp comg G's that have the different gear ratio in the trans that supposedly allows for slightly better mpgs

pretty sure thats the comp but dont quote

2.93's will net better mpgs than 3.29's in the comp g trans

The mileage does seem low too me. With my mods I'm getting around 19-21 mostly city and highway is 29. In town I usually shift at 2500 rpm.

thats what im saying, the only thing i can think of is a lazy o2 sensor or a bad cat that just hasnt thrown a code yet

now i know this is a long shot and the question will make me sound like a noob but can a clogged cat that is causing a restriction transmit heat though the engine and into the transmission causing the trans temps to run hot? it sounds far fetched but its something i wondered about

Originally Posted by NR92

thats what im saying, the only thing i can think of is a lazy o2 sensor or a bad cat that just hasnt thrown a code yet

now i know this is a long shot and the question will make me sound like a noob but can a clogged cat that is causing a restriction transmit heat though the engine and into the transmission causing the trans temps to run hot? it sounds far fetched but its something i wondered about

Not likely.

Is your TC still locking up?

as far as i know, its not throwing a code or going into safe mode (if these cars have that)

Maybe it's time for seafoaming...don't know what the problem could be though. I get crappy mileage as well, but my average speed is 20mph since I work with my car on patrol. On highway it doesn't drink though, thank god!

You guys who live where it's flat have it easy! Granted I have 148K miles but I am lucky to get 23MPG regularly and all highway I get 25 MPG. I have a tune, HV 3, open cone and 3" downpipe. Mine's a GT.