You don't think of an answer and neither would we agree without any testings to find out what is wrong.
Is the cooling fan working?
Is the coolant level correct?
The missing thermostat is not surprising. Many shade tree mechanics tends to remove them when there is an overheating problem, hoping that it would solve the problem.
Is there oil in coolant and/or coolant in engine oil?

Answered by KHLow2008 (expert)
39,956 answers provided

It is none of those.... cooling fan is working. Coolant level cvorrect. The thermostat is missing. no oil in coolant or coolant in oil.

Response from pollyparewirihana
2 questions asked

Does the overheating occur only when stopped?
How high does the temperature shows?
Is coolant spilling out of recovery tank?
Install the thermostat and see what happens.
When does the cooling fan come on? Does it stop after running for a brief period?
What other diagnostic test have you done?

Answered by KHLow2008 (expert)
39,956 answers provided