I think checking out a faulty sensor/gauge/wiring would be a legit thing especially since you say it cools down fast, or like pampered said that a hose is collapsing. When I got the Chevelle on the road it would overheat like it was nobodys business really fast, and it was a rebuilt radiator, but as soon as I went to the Be Cool those problems stopped. Start narrowing it down and replace the small stuff for added insurance.
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