Engine Temp

My brother has a 96 Blazer and i noticed that his temps always run the main line below 210, however my 99 runs constant 210. What is going on?

What engines do you have?? Are you running AC more than he is? How many miles on each? Dexcool could be sludging up on you and you need a full acid flush.... Could be something as innocuous as the thermostat... But let's start with the engine configurations, what do you both have?

Ok my truck almost overheated yesterday, it got up to the 3/4 mark. I had a friend of mine that is a mechanic look at it, and he said it just needs a thermostat. Our engines are the same, the guy is going to put a lower temp thermo in for me.