No heat

[nickaluch]

i have a 1995 geo prism that is throwing very little heat.I replaced the thermostat and changed the anti freeze with no luck.I am guessing the heater core is clogged.is there any way to unclog it ,or do i have to repalce it.And if I do have to replace it, any idea how much$.I heard you get killed in labor

 

[river_rat]

Heat valve opening?
If it turnes out to be plugged up core, ya, they are $$ to replace. Seems they start with the heater core and build the car around it with no thought toward future repairs.

Make sure you burped all the air out of the colling system? If it's low, the heat is first to go.

 

[robshelton]

As above, check and be sure the heater control valve is opening all the way and the system is totally full. When you add coolant it's important to have the temp control set to hot so it bleeds out any air. Baring that, I'd try some radiator cleaner and see what happens.

 

[Pop_Rivit]

Is it possible to flush the heater core? I once had a car that had very poor heat-I cut both hoses to the heater core and flushed it backwards for several minutes. The amount of garbage that came out was surprising, and after I flushed it the heat worked great.

Another possibility is a temperature blend door that's not operating. I'm assuming there is a method to blend the hot and cold air-if something isn't working it may be "stuck" on the cold setting even though you're calling for heat.

 

[demarpaint]

Once you are sure the heater control valve and heater vent {blend} door is working properly, be certain the system is properly bled, especially if you recently changed the anti freeze. If all that is in good order then you can disconnect both heater hoses and flush out the heater core via the inlet hose. You'll have to check to see which hose is the inlet hose. I lost heat in my 95 Caprice and in less than 15 minutes I had it restored flushing out the heater core.

 

[AdRock]

I agree with the above. If the valve is good backflush the heater core.

 

[j_mac]

YES! Backflush the heater core!
Before you cut the hoses be sure and feel which one is the coldest (make sure the engine is fully warm and you've been running the heater.) The cold hose is the exit side of the core. Thats the one you want to hook your garden hose up to. The best way, once you have the garden hose hooked up is to pinch off the hose with needle nose vice grips wrapped in duct tape and repeatedly snap them open in order to "blast" the sludge loose.