My lexus AD 1994 is
Hello Malena,
Here are some tips to try, to narrow the search for the fault.
1. check coolant niveau, refill to the mark, see if there are leaks anywhere from your car.
2. take out the thermostat (usually located inside a "house" where the rubber hoses from the radiator, meets the block), and put it in boiling water to see if it works(should open at a given temp). or replace with a new one.
3. Do you hear a whining or grinding noise from the waterpump? If so, the waterpump should be replaced.
4. It can also be trapped air in the system, squeese the rubber hoses, and refill coolant.
If there are none of the above, there might be a more serious problem, like head gasket or cracked head.
I hope this helped, and good luck, hope everything works out fine for you.
Best regards
Per