OK... so I'm working on this 2003 S2...

This is an auction car I'm fixing up for someone. When test driving it after doing some headwork, I find the heater doesn't work. I didn't mess with it, so I'm pretty sure it's nothing I did. What happens is... it just never blows hot. Blower works OK, and I've actually gone through the trouble of removing the dash to get to the heater box to verify the diverter works fine.

So- when you dial in the temp, the mix motor works properly, moving the diverter and cable to full hot. The valve works fine, and is not blocked. It's adjusted properly and fully opens when the temp control is turned. I verified that the heater core is not blocked (flushed it, there is no resistance to flow). I also verified the two hard lines on the firewall flow fine, as well as the soft lines to/from the heater core and valve.

The engine warms up OK, but the air doesn't get hot when the temp control is turned to hot. There does not appear to be any binding of the diverter, and as I said the cable moves the proper amount, enough to open the valve all the way.

What I have not done is check the thermostat (should not be related, but maybe it's jacked and somehow blocking the heater supply line?). I have also not checked the hoses under the IM for blockage. As near as I can tell there are no kinks.

Finally, the heater hoses are routed properly.

Any ideas? Out of all the S2's I have worked on, actually in 20 years of working on Hondas, I've never seen this. I expected an electrical issue or a cable binding issue and was shocked when all the stuff behind the dash checked out OK.

 

could be an air lock issue in the cooling system, sometimes you have to burp them a few times to get all of the air out. A bad thermostat is possible too. We used to see this in the old days as heater cores got limed up with deposits and crud, I wouldn't expect it on an s2000 with so few years on it.

 

The system has been bled 2 or 3 times now. I thought about that and suppose I'll try it a little harder again. If this is the case, I've never had this much trouble burping an S2!

I checked the t-stat last night, and while it's not perfect (started opening a few degrees past spec, didn't fully open until about 10 degrees past spec) it shouldn't be the issue. If anything, it should help the heater work better. The internal gasket didn't have any leaks.

I also didn't see any blockages in the thermostat housing.

One important item I forgot to note is that the heater hoses don't get warm when running the car & heat. I even disconnected the cable and manually opened the heater valve, while operating the controls. Still no heat. A 2-channel temp meter verified there was NO heating whatsoever (in fact, the air coming through the vents lost a few degrees).

I guess I'll reassemble it, bleed it well, and go back to troubleshooting the shit inside the car. I though I covered it all but I obviously missed something.

The fact that the heater hoses never get hot has me concerned, though. That would seem to be telltale to me.

I've verfied now, the heater core is clear as well as all the plumbing except for the two hoses under the manifold. I think they are fine, though, as I can pour water in the return from the heater (that goes under the rear of the IM) and it drains into the block just fine. If there's a blockage it would have to be on the suction side of the pump or at the outlet between it and the hard heater pipe, since I can't get it it easily to check it.

 

Do the cooling fans cycle normally with the usual temp on the gauge cluster? I remember having a hard time burping my '02 when I changed my thermostat years ago, and I am pretty sure it wouldn't blow hot either. I believe the fix was to go terrorize the neighborhood at the car's limits (hard accel, hard engine breaking, hard corners)

 

try jacking the front of the car up and burping the colling system, also crack the two bleeders to get as much air out as possible. There is one near the firewall that often gets missed.

 

Already did that. Will try it again and attempt to do it better I suppose. I didn't test drive it a lot the first time around, just got it hot and let it idle while dicking with the heater. I may have gotten some air in it, but it usually takes a lot to get the heater to not work. I'll post back when I have an update.

Thanks guys!

 

there is a certain way to do it and its in the Helms manual, i will upload the pages in a few for you

 

 

You got to check you why there is no coolant flow through the hoses. Maybe the hoses are pinched, or something else was done when the head was off. Did you install a Honda head gasket?

 

try bypassing the valve in the engine bay above the header on the fire wall. i had an issue with this when i bent the bracket for my turbo downpipe. i unclipped the cable and i just kinda snapped it in place wherever and i didnt get heat. i had to clip in to the original location to get heat.