Join Date: May 2004
Location: Morganville, NJ
Thanked 21 Times in 17 Posts
Before you try to replace the heater core try this:
Make 100% sure that the temperature knob on the dash is NOT broken. It is so common on those cars due to the fact that you're pulling the cable for the heater control valve. If there's any stiffness in the cable the knob breaks.
If that's ok move on to this:
Drain all the coolant from the car.
Gain access to the 2 heater hoses going to the heater core.
Have about two 3' sections of 5/8" heater hose available. Have 2 gallons of Type 2.
Remove the 2 hoses from the core.
Put each section onto the core's pipes.
Take a garden hose, and stick it into 1 of the hoses, place the other in a 5 gallon bucket. Run the hose at FULL pressure through the hoses and core.
Then remove the hose and put it on the other one, so you can reverse flush it.
If when doing this you can't get any flow through the core, you're screwed. If you do, great.
Now, if you had flow, take an air source and gently blow all the water out of the core.
Connect the hose without the valve on it.
Check the hose with the valve, that the valve actually opens all the way.
Once you've verified the valve is capable of opening all the way. Put that hose back on the core.
Now, open the bleeder above the thermostat housing and fill the system with the new Type 2 you bought until coolant flows from the bleeder and close it.
Complete filling the radiator and cleaned out reserve tank.
Put the cap on, start the car, run it at 2000 rpm for about a minute, carefully remove the cap, and top off as the core will have filled.
Put the cap on. Run the engine at 3000 rpm for at least 5 minutes. You should have very good heat (place system on face vents with full heat). A very good vent temp should be what I got out of a 2004 Civic coupe (195 at 3000, 170 at idle).
If you still don't have heat, it's time to find out whether your water pump is actually pumping.
Sapphire blue '04 V6 6 speed w/ full HFP, comptech ss, momo shadow, TL-S 27.2h/20 bars, intake spacer, retro chrome MH1 HIR2 highs, hella DE fogs, EBC Ultimax, subwoofer/amp, infinity rears, HD Radio, aux adapter, navi conversion.
Vermilion 1999 SVT F150 Lightning, Sylvania/Visteon Xenarc HID headlamps, '01 L turn/marker lamps, PIAA fogs, '01 up Bilstein shocks, all Pioneer speakers, Clarion subwoofer. All Redline fluids.
Silverstone 2003 Honda S2000, bone stock