Thread: Terrible Gas Mileage!

Have an 04 GTP lighlty modded. It is overkilled, has intake, catback, no res, and 180 t stat. It has never got really good fuel economy now but the past few months this winter are terrible I will be lucky to get 300+ km to a tank (187 miles) and the tank im on now I dont even think ill get 275 km out of it (165-170 miles). Now this is mostly city driving but the odd time hi way.

Plugs and wires were actually recently changed, could the t stat be messed up? Could the tune be affecting it running really cold also the temp never gets warm really always stays between the very first bar and 2nd! Also more info the rear 02 sensor went bad a while ago and was replaced with a cheap one and the p0135 never went away had it cleared..could this be affecting as well? I really have no idea here other than this car is POS on gas always use 91 octane also.

Any ideas?

Winter mix fuel reduces gas mileage

Super cold temps reduce gas mileage

Driving whilst the engine is still warming up reduces gas mileage

Leaving the car sitting there idling whilst it is cold to warm it up reduces gas mileage.

A bad 02 sensor will reduce gas mileage.

Originally Posted by machinegunsquid

Winter mix fuel reduces gas mileage

Super cold temps reduce gas mileage

Driving whilst the engine is still warming up reduces gas mileage

Leaving the car sitting there idling whilst it is cold to warm it up reduces gas mileage.

A bad 02 sensor will reduce gas mileage.

Yes all true but never been this bad in winters I don't recall. Anyone have any idea why the car never warms up? Also am in canada gets pretty cold

that 180 t stat is a joke, put the 195 back in.

If the car never warms up, then it is still in enrichment mode (dumps extra fuel to get the engine to operating temperature)

So you're in Canada with extremely cold weather and are running a 180* thermostat. Put the stock thermostat back in, and block 1/2 the radiator with a sheet of cardboard and it'll warm up.

Originally Posted by machinegunsquid

If the car never warms up, then it is still in enrichment mode (dumps extra fuel to get the engine to operating temperature)

So you're in Canada with extremely cold weather and are running a 180* thermostat. Put the stock thermostat back in, and block 1/2 the radiator with a sheet of cardboard and it'll warm up.

Stupid stupid stupid. Please don't listen to this nonsense.

gm cars like to run at 210 degs, modded or not, this cooler t stat stuff does nothing for performance in new cars.


blocking the rad would be step one before the new t stat, as its free to do. and takes a minute to drop it in there. just watch your temps, if it gets to hot, make the card board smaller.

could the t stat also be stuck open at the moment or something?

thanks for info probably gonna start with the t stat back to 195.

if the engine is running to cold it could be.

with the cold temps outside and the 180 it could also be enough, especially if the fans are tuned to come on at cooler temps.

It could. When I had my 180 t-stat it warmed up pretty quick and stayed around 185 in the winter. I don't think the fuel trims are any different at 185 vs being at the stock t-stat temps at 196 ish. Is it getting to 180 in the first 10-15 minutes? It should.

Originally Posted by 02NavyBlue

It could. When I had my 180 t-stat it warmed up pretty quick and stayed around 185 in the winter. I don't think the fuel trims are any different at 185 vs being at the stock t-stat temps at 196 ish. Is it getting to 180 in the first 10-15 minutes? It should.

mine has not gone past the 167 mark this whole winter? what is up?

Fuel trims shouldn't be any different between the 2 thermostats, but the fuel trims between a properly warmed up engine, and an engine that can't get up to operating temp sure are different.

slip a piece of cardboard in there, get the temp to the 1/2 way mark, see how things go. thats to cold. your heat must be rather weak too.

Originally Posted by tc300

What would cause motor not to warm up?? Just a low temp t stat or could there be another issue??

stuck open t stat in these cold temps will keep it from getting up to temp.

or maybe just the 180 and the fans being tuned to a cooler temp will also do this.

theres no reason at the end of the day to run a 180 t stat. no benefit at all. not even in the hot summer months.

ya the heat is really weak as well gonna try the cardboard thing don;t have time to change t stat yet

You said you replaced the rear 02 but you have code p0135, p0135 is for the front 02 not the rear.

Symptoms You will likely notice poor fuel economy the illumination of the MIL.

Read more at: http://www.obd-codes.com/p0135
Copyright © OBD-Codes.com

Get a scantool and watch your car warm up. If its around freezing outside your car should get to 180* and hover withen 10* of that withen 5 to 10 minutes of driving. If it never reaches 180 you probably have a bad thermostat so put a new one in.

Be careful whos advice you take on here. Not only will a 180tstat not cause heat issues but it also is well above the warmup tables in the engine computer so it will cause little to no change in fuel economy. A 160tstat will however cause heat issues and a noticeable loss in economy.

Also again be careful of advice you get. Cardboard will do ABSOLUTELY NOTHING to help your car warm up. There is only one thing on this planet that keeps your car warm in the winter and that is the thermostat. It is completely closed and basicly air tight until your car warms up. I would love for someone to explain how blocking your radiator WHICH ISNT ****ING CONNECTED WHILE YOUR CAR IS WARMING UP will do any good. All your going to do is risk overheating on a warm day going up a hill.

Sorry for the rant. I just hate when people who don't know what they are talking about give terrible advice. Time for me to go out and warm up the 2.55" pullied monster in my driveway for work.

Someone's panties need to be changed.

Partially blocking the radiator will help regulate the temperature in the cooling system, keeping it at operating temperature when it's cold as balls out. Sure, warm the car up to operating temps, then go drive it at 70mph in 0* weather and watch it go back down.

No, you should not block the whole radiator, and no it won't help it warm up any if the thermostat is functioning properly, it will only help maintain that temperature.