Volvo Repair: Poor fuel economy, poor fuel economy, proper diagnosis

Question
Hello there, I'm not very familiar with automobiles or their associated repair, but after several attempts at bringing my 87 240 DL into a mechanic, the problem always remains despite repairs.

I am getting extremely poor fuel economy.  The tank holds 15.6 gallons of fuel, and I'm lucky to reach 200 miles on a single tank fill.  The car idles rough, but it seems that its a common occurance in Volvos of that model.  There's also a slight pause in acceleration when getting on the freeway, but it doesn't seem to be a problem in city traffic. Once the car gets going it accelerates just fine.

It might also have a corrolation with thermal problems I've been having.  The car seems to get very warm, very quickly. I've had the radiator tested for leaks and new coolant added recently, but it didn't affect the problem.

Do you have any ideas on what may cause these problems and how to go about fixing them? it looks like I'll have to see if I can do most of them on my own.

Thanks again.

Answer
the runnign condition could be caused by many things.it will really need to be looked at for a proper diagnosis.

the heating up problem could be a clogged radiator either on the inside or outside.ther could be a clog in the engine,the thermostat could be bad.there could also be a problem with the head gasket or leak in the cylinder head.it will need to be looked at for a proper diagnosis.