87 Firebird overheating

My son has an 87 Firebird with a 2.8 litre V6. It has recently started to overheat, but intermittently. The rad fluid boils in the overflow container, but then seems fine the next time he drives it.
Any suggestions? Someone mentioned a head gasket?
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I had a bad thermostat. A new one fixed the problem. Also if it has electric fans, if you want to keep them on all the time or by a switch there is a green wire to the fan relays, ground that wire out to turn on a fan.

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By intermittent I mean it happened twice for now apparent reason. The car was only on for about 10 minutes. It wasn't on the highway or idling in traffic. It has operated fine, without overheating for several days since, both on the highway and in the city. I changed the thermostat this evening, thinking it maybe stuck. What about an air lock?
Terry
CBHvac wrote:

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My 1992 Camaro required a thermostat replacement and a fan switch...
Good Luck... Charles

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