Well, I just drove an hour and a half trying to keep my water temp out of the red. I got a 91 Civic DX, completely stock d15.

Here's the deal, the gauge would increase as I press on the pedal, stay the same when I would keep a constant speed, and fall if I let of the gas (usually pretty drasticly). Towards the end of my drive, after I entered the city, the gauge would basicly stay up until I completely got off the gas and just coasted.

I am wondering if my water pump was going, or if it is my radiator. I'm pretty sure my thermostat is alright. Seems like my gauge would have gone up when cruising if it was my pump. I know my radiator isn't the best because I blew a head gasket last year and drove on it (fried it a little bit). I don't really know, it's dark and I can't check on it right now...

Any advice/suggestions/comments?

 

It could be your water pump. Is your fan turning on? It could just be the guage is bad.

 

This may sound dumb but have you checked your coolant level?

Mine did something similar the other day, and it turned out that I had a small leak over time and I was waaaay low on coolant.

See if any of your hoses look old or deteriorated, and I dont just mean the upper and lower radiator hoses. Make sure you check all the ones in the back for the IACV, heater, etc.