92 Rodeo Heating Up

I have a question...I just bought a used 1992 Rodeo and everytime I drive it, not for a very long period of time at all, it heats up to very high temperature, then it suddenly cools down, very quickly. I am wondering, and I am sure it could be a million things, but where should I start in attempting to fix this problem? any info would be appreciated thanks.
Adina in az

sounds like the thermostat is sticking.

If you have the OEM radiator in it I would seriously think about replacing that too.

Thank you so much, the thermostat is what we thought too. I appreciate your assistance!