Cadillac Repair: fuel consumption, poor fuel economy, fuel mileage

Question
Kevin,
145,000 on 1993 DeVille.Ditigal read out shows 15 mpg,but trip od. shows 8-9 gals. No smell of gas. Tune -up done 19,000 ago Clean air filter.
No problem w/ fuel before fluhing rad. Flushed because no heat.Now have some heat,but poor fuel economy. Thanks for your time.  Wm

Answer
William,
I'm assuming that you mean that your calculated MPG using the trip odometer shows 8-9MPG but the car's trip computer is showing 15MPG average. Is this correct? And beyond this, you say that you recently had work done to the car (rad. flush) and ever since, you feel your MPG is down?
If so, this is most likely due to either something that was left disconnected by the shop doing the work, or possibly since the flush, the engine is not getting warm enough to put the PCM into "Closed-Loop" operation. If the system is remaining in "Open-Loop", it will be running much richer than it should be. This might make the car "feel" like it's running quite well but is in fact killing your fuel mileage and possibly damaging the catalytic converter.
Are you seeing any warning lights or messages of any kind?
Are you familiar with how to access the OBD (On-Board Diagnostic) system?
Let's hold-up here until you follow-up on my questions, so I can make sure we're on the same page.