I recently replaced the cooling fan, and ever since I've been having issues with gas gauge fluctuating & gas running out quickly. It was super great on gas before replacing the fan, and now it seems like it's eating way too much gas. What could be causing this?

 

They are not likely related at all - Fan vrs gas mileage.

What was the gas mileage before replacing the fan - and what is it currently?

 

I'm not really sure, however the gas gauge is fluctuating it can go from 122miles of fuel remaining to 55miles in a matter of minutes.

 

Do you mean you are basing this, on the display that shows the estimate of the distance left in the gas tank? Not on actual gas mileage, or the actual gas gauge.

 

Is the a/c on, is the switch set to defrost, is the switch set to recirc?

 

Sound more like a fule sending unit

 

This might be what she is referring to - if you park/drive the car with the front uphill, you will notice the estimated distance you can drive on the exisiting fuel is quite a bit LOWER than once you drive for a few minutes on level ground. It will increase quite quickly once you start driving on the level.

Conversely, if you park/drive it pointing downhill, the distance estimated is MORE than the actual distance left.

I almost got caught by that a few years ago on a trip - I checked the distance remaining just as I approached the last gas station (next one was about 100 miles away), and the display said I had lots to spare. I totally forgot I was heading downhill and it was actually over estimating the distance. A few miles down the road I checked it again, as I was heading up to the summit of a mountain pass - gulp!!!! I was going to be about 20 miles short!! Once on the level I checked it again, and could see it was going to VERY close. I did make it, but the tank took the full amount as listed in the manual for the tank capacity.

So you can only really count on any sort of accuracy when driving on the level.