Bob---obviously fluid getting on a hot exhaust is a bad deal. So---Yes, firesleeving does insulate the hose, and with that 'probably' does lower the fluid temperature. I say 'probably" because we havent put probes in to measure the temps.
I do know for sure the the hose I mentioned in a previous post on a well known VAF member----if he wants to comment here thats cool--would have failed and a probable fire would have happened. In Flight or otherwise, but I'm certain that the combination of firesleeve and teflon hose kept a disaster from happening.
Whether guys want to use firesleeving is their choice, since they are the manufacturer of their planes. We make recommendations based on experience, and generally accepted standards. In the building process, if routing a hose close to a muffler, or exhaust close to the cylinders is necessary, I'd sleeve them, AND add heat shields to protect the hose. If at all possible, I'd re-route to help the situation.
Lets face it, in a fire, having firesleeve or not may be a moot point. But, if it delays exposure of the hose, and its fluids, then its worth it to me.
Tom