In the last couple of weeks, it's been hot here, in the 90's or so. My van runs normal on the highway, around 180-190 degrees. If I am in traffic or on hard throttle up a hill the temp guage climbs to 235 degrees, with or without a/c on. Let off the gas and coast down the hill or drive 65-70 mph and it returns to normal. The coolant level is full and never overheats and blows any coolant out. Just started this recently. In the past when it's this hot, this has never occured before. Van has 193000 miles on it and runs fine. Any ideas?

 

Guessing here but maybe the transmission cooler has something to do with it? If the truck is heavily loaded the trans will build a lot of heat too. You may simply be overwhelming the cooling system.

 

Try backflushing the radiator and change the coolant. You may also have some blockage in the engine block.