Motors. temperature rising/oveheating in traffic

most temp guages use color coding instead of numbers because its less confusing to most drivers..red generally means operating temps are higher than is reccomended by the manufacturer to run safely.. this should tell you to check the overall systen for issues like low coolant or malfunctioning parts in the system...most guages I have ever seen run close to halfway up most of the time..(except my 92 dodge which stays under a quarter way over unless its parked in heavy traffic then it goes way up and I am forced to turn on the heater in extweme cases..) just to be sure , look over the system or have someone who knows look at it to insure it is fine. otherwise you will need to idle the car in a parked spot and just observe it for about a half hour and see if it overheats or anything...good luck..

could be a cracked block engine.what i would do is put a tarp or old sheet down park vehicle on it and wait then when you check you can look on old sheet to see where its leaking and it will give you an idea where to look for the leek if it was head gasket youd have sludgey looking whitesh foam in the oil

If the light is amber is is your check engine light. If the light is red it would be the oil light or temperature depending on weather you have guages or not.

A van that is only 2 years old shouldn't have a cooling system breakdown. I think that with the hot humid weather this year your cooling system doesn't have enough extra cooling capacity. I would look at separating transmission and oil coolers from the rad to their own coolers to take the pressure off the rad. You should also probably look at putting in a larger rad and/or fan to help keep the temperature closer to normal.
That's my 2 cents. Hope it helps.

If changing the thermostat didn't work, have the heater control valve checked, it may not be opening all the way to let the coolant circulate thru the heater core fully.