Before you spend too much more money, check the cooling system in a methodical way, starting with the stuff that's easy and/or cheap to do. 1. Engine cold, is there any coolant in the system? Not enough coolant will make the motor run hot. Top up the radiator and expansion tank if it's low. Then find out why it is low. 2. Check the hoses are good (and that the clamps are tight). If the hoses feel crusty when you squeeze them, swap them out. 3. Is your radiator leaking? Look for crusty white-ish deposits around, on or underneath it, that is a leak. 4. Look inside the radiator, do you see oil in there? That is possibly a blown head gasket. Is it full of calcium? That will impair the cooling. Are the fins in good condition or blocked with cr@p? Air needs to flow through it for it to work. 5. Get a new radiator cap while you're there. They're $20 or less. Weak caps allow coolant to boil off. 6. Look under the oil filler cap. If it's milky pale brown sludge it means water is in the oil (possible gasket failure but not always). 7. Inspect your water pump. Look under the car for visible leaks. Water pump housings have a small "witness" hole in them. If the pump seal fails, coolant enters the housing and drips out of the hole thoughtfully provided exactly for that purpose. You will see drops of coolant on the ground directly underneath it when you park up. 8. Look at the exhaust - clouds of steam out of the exhaust is indicative of a blown gasket.
9. Assuming you find anything more serious than just a loose hose, the next step is to confirm your diagnosis. Get a tech to pressure test your radiator. They will confirm if the system is holding pressure (as it should). They can/may also do a "sniff" test for oil in coolant and vice versa.