Hello to All,

Any comments or advice is greatly appreciated. Thanks for your time and help.

I am considering changing the fuel filter on my 240 '89 wagon. 1) I'm pretty sure it hasn't been done in a while. I've done or had many things done on her that have proved it has not been well maintained. Fortunately, it is in decent shape with barely any rust at all(california origins) and drives pretty well.
2) My mpg is only around 16-20. I was thinking this might have something to do with an old fuel filter or a oxygen sensor needing to be replaced. Plan on doing oxygen sensor soon, once I do the throttle body gasket and clean out the intake mainfold.

I've had some issues smelling gasoline after I fill the tank up beyond 1/2 way. This might be the gasoline expanding in the heat though as it is summer and I didn't really notice this in the winter or spring. I know a gas leak is pretty hard to detect as the gas evaporates, but is there any other way to detect and should I maybe be a little more diligent with specific time increments when logging the mileage and fuel changes.

ALso, when I change the fuel filter I plan on using a pneumatic gun and examining the lines going from the filter to the pump and to the tank. WOuld hte soapy water trick work for detecting a leak?
I know everyone talks about the perils of changing the fuel filter, but I don't think there's too much that could phase me at this point. Having changed the blower motor and replaced the trail arm bushings I feel pretty confident in my abilities to handle the volvo's toughest repair jobs. But any kind advice for the fuel filter would be much appreciated.