I recently drove about 300 miles round trip (highway miles) and ended up only getting about 11 miles to the gallon. My trailblazer keeps getting increasingly worse gas mileage but has no check engines lights or codes on. I know it will never get really good gas mileage but I used to get 16-19 mpg depending on my driving. This is getting very expensive. Please let me know what I should or can do to get it back to where it should be. I am currently at 153,000 miles (I know that is alot but it is still a good truck) Thanks! I am prob about due for an oil change also.
2002 Trailblazer getting increasingly worse gas mileage Please Help!
- Thread starter Lacher
- Start date
gmcman
Member
- Dec 12, 2011
- 4,656
There is alot of info here on this, generally you will find that an old thermostat/ temp sensor will drop the coolant temp to about 2 or more ticks to the left of straight up on the gauge, this will hurt mileage. Replace both at the same time with GM parts.
Another issue is old plugs, replace with AC Delco 41-103 along with your upstream O2 sensor. If the sensor has more than 80K miles on it and plugs are new then replace sensor anyway. You can check the sensor with a live data scan tool and refresh rate should be at least 1HZ or faster..they get lazy as they age.
Another issue is the fan clutch, if it doesn't fully disengage it will hog down MPG's as well. Should turn slowly when idling and you can carefully take a rag and try to stop it from the smooth edge. When hot it's engaged naturally but when it disengaged it turns but only under light viscous friction.
These are the 3 general issues with poor mileage and something easy to check.
Another issue is old plugs, replace with AC Delco 41-103 along with your upstream O2 sensor. If the sensor has more than 80K miles on it and plugs are new then replace sensor anyway. You can check the sensor with a live data scan tool and refresh rate should be at least 1HZ or faster..they get lazy as they age.
Another issue is the fan clutch, if it doesn't fully disengage it will hog down MPG's as well. Should turn slowly when idling and you can carefully take a rag and try to stop it from the smooth edge. When hot it's engaged naturally but when it disengaged it turns but only under light viscous friction.
These are the 3 general issues with poor mileage and something easy to check.
Wooluf1952
Member
BlazingTrails
Member
- Apr 27, 2014
- 19,409
I'm leaning towards the cat, also I would remove the injectors and have them micro cleaned and tested. Plugs and coils. I have brought mine up from 14 mpg to currently 18.
DocBrown
Member
- Dec 8, 2011
- 501
Wooluf1952 said:
My thoughts exactly. The mileage has dropped too far to be one of the usual suspects. A bad thermostat in itself will drop mileage a little, but the computer will try and make up for it by running rich, which over time causes the cat to melt inside. More often than not there is no code just really bad mileage and a feeling of the engine struggling to get up to speed. Been there, done that. It usually happens between 80 and 120k.
Also you might fill out the vehicle info in your profile so we can help you make a better diagnosis.
I changed my air and fuel filter recently on my 02' LT (229500mi) and my mileage jumped from averaging 12/16 to 16/21MPG (city/highway) --- I even got 23MPG on a trip driving 55MPH religiously. I was very happy with the improvements. That's a extra 40-50 miles per tank.
That said, I may look into the above as well since I have to change the exhaust manifold as it has a leak off the block and downstream. I'm waiting until spring to minimize bolts breaking.
That said, I may look into the above as well since I have to change the exhaust manifold as it has a leak off the block and downstream. I'm waiting until spring to minimize bolts breaking.