Poor Gas Mileage - Check you temperature sending units

[Biggles]

I have a 98 4.0L V6 I used to get 320+ MPG in town and 420+ on the freeway. About a year ago my mileage dropped off to 200-220 and not much better on the freeway.
I have been readin about all the thing to do to improve mileage and started making sure the basics were in order including cleaning out the whole intake system.
A couple of weeks ago I realised that the dash board temperature gauge was showing a lower than normal temperature. It was not much just about 1/8 inch swing of the needle down. It then occured to me that while the temperature of the engine is below normal (190+/-) that the computer would still think the car is warming up and put more fule into the system.

I dont have a OBDII box to read the temperature to just replaced the T'Stat and both temperature sensors. It was an easy job but required removing the air intake system.

Now the dash display shows about middle of the dial. The engine does not ping and ....... the mileage has jumped up to 320+ running around town with many short 4 mile trips.

Next week I will do a 700 mile trip to Lubbock and back and hope to get back to the original 420+ MPG.

So my message for all the people that I read talking about 200 miles per tank... check your temperature sending units.

 

[schmidlkofer]

very interesting....my gauge does not go to normall....where is the temp sending unit?

 

[tipdrill]

yes this is interesting. my temp gauge is never in the middle and the gauge sometimes has trouble moving in the winter, which results in the "Check Gauge" light illuminating.

is yours a SOHC?

 

[aldive]

I have a 98 4.0L V6 I used to get 320+ MPG in town and 420+ on the freeway. .

Thats some impressive mileage.

 

[Biggles]

I think I was a little over enthusiastic. That should have been miles per tank.

 

[Biggles]

I have a 98 4.0L V6 SOHC.
The temperature sensors. sending units are just behine the T'Stat in the middle front of the engine. To remove them you have to take off the complete air intake system including the plastic upper air intake manifold.
Its an easy task, just take a couple of hours of nuts and bolts no major problems.

 

[Biggles]

I knew my sensor was possibly faulty as the gauge neddle was below the picture on the guage when normally it came to about half way or just over the picture of the thermometer.

 

[schmidlkofer]

i have the 4.0 its not the sohc tho...