Without dismantling the entire dash to get inside the heater box, I wonder what you can see if you look in where the cabin-air filter is? You might also be able to remove the blower down from the bottom of the ductwork above the passenger's feet.

edit... Now that I think about it, I bet the AC evaporator will block your view from the blower into the heater box.

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Not sure how much is different Civic vs. Accord or for that matter for different generation Accords...

 

Well, his Civic is a 6th gen (98) if that helps. Like I said, I haven't really gone looking myself, but rather trying to get some ideas on where to look. Yes, we flushed the heater core both ways, as that was my first thought. Then he replaced the valve and hoses while he had the engine out (for rebuilding). He's also changed the "T" stat twice (with genuine Honda), but is still not getting heat. Yes, the temp gauge goes up to about the middle of the cold to mid level of the gauge (about the 1/4 mark), and the cooling fan does cycle after the engine gets warm and up to running temperature. This is why I'm confused, as it should be working, unless it's something we're not seeing or we missed.

OP, I'm sorry if we hijacked your thread, but I'm on HAF more than any of the Civic forums.

 

That Civic still has the D-series engine, right? That makes it kinda similar to a 99 Accord, only 7/8-size... So in general terms the same advice should apply. No guarantees that you'll both find the same cause for the problem, but you both have to check all the same things until you find something actually wrong.

Bleed air out of the cooling system with a bleed screw at the thermostat housing?

6for2...
Have you checked the coolant level in the actual radiator? There's circumstances where the radiator and/or heater core can get filled with air while the white plastic overflow bottle is nice & full.

How about the temperatures of the 2 heater hoses right where they go through the firewall? If they're hot like water is circulating properly, then I'd quit with the water-side and start looking for problems on the air-side like damper doors that aren't actually working.

 

OK I'm mixing up 6for2 vs. Toecutter...

How about a blockage in the water hoses between the engine & firewall?

This is gonna cost you a bottle of antifreeze, but maybe you have to disconnect the hoses from the valve, to verify the valve itself isn't blocked. Or maybe the lever is working but it's broken off from the internals of the valve? Or a blockage in the hoses closer to the engine? I think all of that would be reflected in the heater hoses not getting hot.

 

Yes, it's still a "D" engine. It also got bumped up in piston size by.5mm, and it's also using the 99 style DY8 intake (on a DY7). When he filled the system up, he used 2 gallons of Honda fluid, with the balance of the 2nd jug going into the over flow jug (like called out in the FSM). There's no bleeder valve like the Accord uses though, so I squeezed the hoses to get as much air out as possible.
I double checked the new heater valve (Honda part) that went in, so I know it works, and is clean. Same with the new hoses (clean and no blockages). I did see the level drop some in the white jug. The engine block and head went to my machinist, so I know they got done correctly (he doesn't do anything half azzed).

 

I'm running out of ideas for that Civic.

I still want to see what 6for2 says after checking out those same things on his Accord...

 

OK, Thanks Jim. I'm waiting to see what he/she finds out too.