he's already replaced the cap...

James

 

Everything feels normal to the touch. Upper and lower hoses, both side tanks of the radiator are hot. I'm just dumbfounded as to why the gauge would move like that unless the block/head has a small air pocket in it. However, this JUST started on Monday night. I flushed and refilled the system near the end of July and until now, the gauge hadn't moved like this.

 

I did some checking and it seems that the boiling point of ethylene glycol is 386.8 degrees F.. I found the info here on page 7....Mark