Heater feels like it's on, dial is turned off
 

I heard that the heater core is operational all the time to get rid of excess heat, but is there something wrong with the controls to divert the heat from the cabin? I have done the fix to improve the seal between the engine compartment and the fresh air intake at the base of the windshield-didn't help.
What's the fix to get reasonably cool outside air into the car?
(search "heater" and all you get is coolant reroute and heater core delete)
Thanks,
-JB

When not using it, put the air control on recirculate and cold settings. There is also a write-up on m.net about the flapper on the core not sealing all the way and a fix on getting it to so that no air gets by the cor unless you ask for it.


http://www.miata.net/garage/heater_cable.html

I really need to do this heater door mod!

I have tried all of the possible solutions proposed on the forums. They don't help much. The problem is that the hot water constantly circulating through the heater core heat soaks the whole underdash area.
The solution is to bypass the hot coolant around the heater core. I did that, installing a 3-port valve so that I can heat or not heat. The vents blow much cooler air, even after a short stop, and I run the fan 1 speed lower when using air conditioning. The foot wells are much cooler.
Any other fixes are just pissing in the wind.

Definitely takes care of the heat under the dash, but as you have indicated, the water is rerouted back to the manifold(correctly).

To the OP: Do not just block the heater core or the rear of your motor will get no cooling water.

I plan on installing the BEGI coolant reroute and then installing a water valve before the heater core to shut the water flow off when not needed. Currently I have just bypassed the core for summer but you cannot just plug the lines or you will cut off water flow to the rear of the engine.

If you have done the coolant reroute, then could a simple on/off valve be installed? Since there would be no worrys about the rear cly getting enough coolant flow.

For light driving, sure. But when you are on it, not really. This is because the coolant flow on the Miata is compromised, having originated as a FWD engine. So the active heater helps cool the back of the motor.

Getting the flap to close the whole way takes just five minutes. Drop the glovebox via phillips screw driver under the dash, one screw per hinge. Pull the box out. Reposition the pull cable in its clip mount (no tools) after observing the mechanism. Done.

The reroute takes all the coolant from the rear of the block. You do not need the circulation through the heater or a bypass required by the stock coolant route. The door fix is ok, but it does not solve the root problem of a very hot heater core inside a small area.

Yes I know. BTW lots of engines used to cool from a different end. I loaded in a Renault Fuego Turbo engine into a Europa and had to move the water pump to the other end of the lump. That engine weighs under 200 pounds as it is a pushrod hemi. Once converted, the WP lived above the bell housing lol.

Another cooling strategy used on some race engines involves a manifold that parallels the head. See it above the header on this E30 M3 engine? It's a casting that connects and passes fluid at each cylinder. This idea would work well on Miata engines.

If you: (A) ensure that the heater flap closes all the way when set cold
and (B)have a functioning hood seal near the firewall

Then the blown air (no AC) will be ambient. When I did this to my Miata the air temps dropped at least 10 degrees.

As well as making sure the hood gasket is compressed all along its length and making sure the heater air outlet is actually off when the temp setting is turned to cold, there is a sneak path for hot air from the engine compartment getting into the air intake. The air can go through the drainage holes in the hood braces and particularly the open areas around the windshield washer jets. Use duct tape for large areas and electrical tape for small areas.