Heater Core?? Or Thermo??

I have a 84 civic wagon with some major miles. I bought the car from my dad about ten years ago. Well I`m pretty mechanicly inclined but I need some help with this one. When I turn on the heater it gets hot for about ten seconds then gets cold. Now the radiator hose going into the core is hot and the one coming out is luke warm at best. I was thinking the core was plugged but when I removed the hoses and tried a pressure(blow by) test there was plenty of air movement. Then I followed the hoses to the thermostat housing and there it splits into three directions. Could that hosing be plugged or is it possible the thermostate is stuck just barley open? It will also get hot at higher speeds 70-75?? Any info would be helpfull....

^^^Bump^^^

i would check the termosatt to see if its working and if it is working clean the fins in the radiator and maksure that you fan is working
jeb

Well the radiator (clean)is new. The fan works jut fine on low med. high. Like I said it gets hot for about ten econds then cools. I`m gonna try the thermostate and go from there.

From your description of the heater getting warm and then cooling it sounds like the valve that lets the water into the heater rad is opening to let some water in and then possible closing off by itself and therefore no heat. If the heater hose into the rad is hot the themostat should not be the problem.

The thermostat lets water flow to the engine rad to cool when the engine gets to temperature. The heater rad always has hot water coming to it and the valve in the hose that opens and closes could be the culprit. If you had the hoses off, that's a chore in itself, and the interior rad has good circulation and isn't clogged I don't know what else to tell you. Maybe something is plugging the IN valve. Lets some water in and when the flow starts plugs the hole up. Check the hose on the motor side of the heater valve for blockage.

Hope that helps. JS

its the thermostat... my CRX did the same exact thing. Put in a honda factory thermostat and you should be good. It takes like 20 minutes and 20$ to do it.