(please help!!) overheating/heating issue 1989 volvo 740 turbo 2.3
 

I have only owned this car for a few weeks, One thing I have noticed is it gets very hot inside the car, to the point where is quite unbearable.

I have driven the car on 3 hour drives and would assume if it was an overheating issue with the engine then It would have died by now and the temperature gauge is floating around the middle and seems happy. can anyone suggest why its getting so hot?

Well, is it because it's summer and the outside temperature is may be also hot and you have no working A/C?
Or is heat coming out of the vents meaning there is some vent distribution malfunction?
A closed car in summer time heat even while driven on the highway can get very hot inside...

the air vent selector shoudl normally be at 9 oclock (dashboard vent), the recirc and a/c disable buttons should be pushed in, the heater knob all the way to the right (off) and the fan should be on 1 or 2. under those conditions, the air coming out of the vents should essentially be outside air temp once things are moving. if you're getting heat its quite possible your heater valve is bad or disconnected (its vacuum operated, its in the heater hoses between the back of the engine and the firewall). the heater valve is such that vacuum closes it, no vacuum opens it. open valve == heat. with the engine running, turning the heat control knob should move the lever on the heater valve.

original style heater valve:
https://i23.ebayimg.com/03/i/001/34/22/556a_12.JPG

VDO replacement style:
http://dyw03owr7vs3n.cloudfront.net/...jpg?1313090196

chevy citation cheap valve style
http://www.joetlc.com/images/9447896.jpg

that last one, you can't tell if its opening or closing via visual inspection.

'89 have sliders for the temp. and the various vent direction, not the electronic panel with the circular knobs. Still, the heater valve should be closed or heat will blow in.