id be worried more about letting the temp get super high than something coming loost in the radiator. if i were you i would get it to a radiator shop and let them check it out. the worst you have to replace it thats what $200 or less. just keep an eye on the temp. thank god you have the scanguage to watch it because the cluster gauge doesnt come on till its nearly too late

 

That truck is WAY too hot. 240 is close to death I bet. Has the shop that did the recent motor change has warrantied their work?