its about 20-30s outside right now and my 95 civic ex has problems with heat. i can let a car warm up for 15 min it will get somewhat warm then when i start driving it will cool down almost to the point where it feels like it has just been started, but the idle is normal, at about 800-900rpm. so i can be driving for 30 min and the car would blow half heated air and the thermostat would show cold engine.

anyone know what the problem could be?

 

I had a somewhat similar problem... except my heater blows hot air after that initial warm-up period. I think it's because the cold weather makes each element of the cooling system cold - hoses, radiator, heater core, block, etc. - and so every one of those things is making the hot coolant colder... therefore, even though the engine is at temp, the thermostat opens and BAM, the coolant is instantly chilled by 20-degree hoses and radiator. The temp sensor must detect this... for a while I thought I had a busted thermostat, but it turned out not to be that at all, because after driving for a while it DOES reach normal operating temp and stays there.

Now for a solution... if I turn the heater off while I warm the car up - let the needle get somewhere near normal - and then drive with slightly higher revs than normal, it heats up pretty normally. The other solution is to let it warm up for a longer time, and let the hot coolant slowly warm up all those cold engine parts which have been chilled.

Just my two cents...

 

I would try that, see if you can get the car to warm up all the way with the heat off. It still should blow heat after being warmed up with the heat on, but try the other way and see what happens.

 

I don't know what it is, but thermostat's have been dropping like flies this season. I've never seen so many thermostat problems going through my shop that has gone through this year. And to top it all off my thermostat is sticking open for the first time ever. I'm not saying you defiently have a thermostat problem, but i'd change it anyway due to the thermostat curse of the 2000s. I'm serious this is going down in history. The bible was wrong it wasn't the end of the world for man kind it's the end of the world for cooling systems.