it'll cause a CEL unless you get a MIL eliminator, which you can make yourself or buy from
www.zxtuner.com but I doubt that would help your cooling problems at all. the cat is cooler than your engine. are your fans working good? is your radiator good? is your water pump good? use a 75% water/25% antifreeze solution, it may help out some. and move to a place that's a bit cooler or drive around without the hood on the car.
