My fan has been going on daily after shutdown on rides home from work. I was attributing it the 90+ degree days we've been having.

However, I got stuck in stop and go highway traffic today in a downpour. I just happened to look down to check the time as traffic picked up speed and saw my temp guage in the red! It dropped almost immediately as I got up to speed. I hit one light as I headed in to work and it started to climb gradually. But I got going before I reached the danger zone.

My assumption is that this was a gradual problem and that manifested itself today. I had heat since I jacked it all the way up. I'm not smelling the telltale signs of a head gasket problem and since I was in my work clothes and it was pouring, I didn't get under the hood when I made it to work.

I've done a good deal of work on my cars (just changed a water pump on my old 87 Accord, which I have sice given away). So this isn't foreign territory. But I'd like to try to narrow down the potential causes before I get into it.

I know the coolant needs to be changed but it doesn't seem that simple. Could the really high heat lately degraded poor fluid to unusable in only a couple weeks?

thanks