Fuel mileage and timing are related. Maybe time to check your chain streach and set your timing. Also maybe time to service your injectors.

I haven't had a chance to check the timing chain stretch as it has relatively low millage, 170,000 miles and "i think it's ok" so ill hold of till i get a chance to do it, but i did notice that the car almost always runs cold, the needle on the gauge newer goes past second line above 40c mark. if i push it hard around town it will get up to 80c but come right down if i'm easy on the throttle or stop on the lights. Could the engine running cold be causing my bad fuel millage?

You need a new thermostat and yes you will get poorer fuel mileage from a car that has not fully warmed up but not a whole lot.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10