My car heated up to 255 degrees why

We'd need a little more information of the driving conditions when it got this hot. First check is your coolant level - do this check only on a cold engine. The coolant should be topped full. If it's low, you will need diagnosis to find where the coolant leak is. The next step is to listen if the fans are running when your car is overheating. Either way, it sounds like the van needs to make it into a repair shop for a diagnosis. Engine damage can happen with an overheating engine.