My heater sometimes works well, but often it just blows room temp. air at me. Does anyone know whats going on?

 

Might sound stupid,but the first thing to check is your coolant level. when it's low it doesn't heat as well.

 

Could be a stuck thermostat or a clogged hearter core. Definately check the coolant level first.

 

I have seen this problem often in the s series truck with dex cool. The heater core gets plugged. Just pull the hoses off and put a garden hose to it and flush it.

 

You haven't given us much info, like what kind of weather and what kind of driving you're doing when you have good heat/poor heat .... But this is what I found with my ride which is a 3.8L 3 speed auto with OD and lock up converter and short gearing. I turn about 2000 rpm for 65 mph. And that's most of my daily commute. Right there is the key .... Engine rpm isn't sufficent to force the hot water through the heater. Water like electricty takes the path of least resistance, in this case the radiator with it's larger diameter hoses. What I have to do is get the engine above 3000 rpm to get decent heat. I have to drop out of OD to do this.

Now a question for all out there: Does anyone know of a smaller diameter pully I can use to overdrive the waterpump? I've found underdrive pullys but nothing to speed up the waterpump.