My van overheats. It started gradually on a long road trip, and got worse as we went. I pulled the thermostat along the way, but it didn`t make any difference. When we reached our destination and only used it for short everyday trips, it did not overheat. But on the long way back it got worse, and now just overheats. The radiator seems fine, there`s flow through it, an apparently through the engine as well ??

whenever you have an unexplained loss of coolant...and you positively know your not leaking from the hoses....your car is warning you of impending doom!
My old 89 Beretta had 280k miles on it when i noticed the low coolant light come on, so i topped it off and problem went away, i had no coolant line leaks and just attributed this to old age..i only had to top it off every two weeks, but after a year or so it started getting worse and it was like every week now, after 295k it started running rough and then it went away after driving it about two miles and then it started overheating badly, so i looked inside the radiator and half the coolant was gone, so i felt the upper radiator hose and it was cold, never got hot! it was a stuck thermostat! it was corroded shut! and then i let the car cool completely (took off the radiator cap) and watched it warm up and my worse nightmare was confirmed, bubbles coming out the top and overflowing...blown head gasket!....so my advice is never ever let your car overheat if you can help it, (everytime you do it stresses the gaskets).. and if it does, turn on the heater full blasts, and pull off to the side off the road and check to make sure your fan is working! ...i fixed the problem somewhat though, with "blue devil" gasket sealer, 500 miles after changing five plugs,and runs great, i just cant get the #2 plug out, because that is where the cracked head or gasket problem is. So whenever your car overheats badly or starts to overheat a lot, change out your plugs, and put some antiseize compound on them or you probably wont be able to get them out later when you need too! The old #2 plug only has 10k on it, so i"ll just leave it in, dont want to risk snapping it off!
Blue devil is a bandaid fix!...the correct way to fix your "low mileage" vehicle is to forkout the grand it will take to changeout the gaskets.