overheating

have a ford ea sedan...when towing my boat occasionally it heats up to near boiling point and heater runs cold....problem suddenly stops car cools down
and heater runs hot again..only happens every now and then , and regardless of outside temperature... any ideas...
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Sounds like you are low on coolant or your thermostat is bad.
Gitfilder wrote:

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if i was you i would check to see if yor head gasket has gone
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