Bypass Heater Core - valve
 

There have been lots of discussions about bypassing the heater core to reduce cabin temp. The temperature coming from the heater even with the climate control turned down is brutal on hot days. Only made worse by the reduced air flow to the air conditioning condenser and, subsequent, reduced AC cooling. It only got worse after installing the Fab9 GT turbo. I found some older discussions on another forum, but nothing current. Has anyone come up with a great kit (or your list of parts) for controlling the flow of coolant through the heater core. I'd be happy with a clean ball valve sort of setup so that I could manually enable/bypass the heater. I'm aware this may reduce defroster efficiency, but I can live with this as I drive for fun in nice weather. If I need more defrost, I can open the valve. With the turbo, space is a bit limited.
https://cimg5.ibsrv.net/gimg/www.mia...e4f3a14741.jpg

It's been a while and my memory sucks, so you'll have to forgive my lack of detail, but the hot/cold knob can get out of adjustment so it allows some hot air through the vents even when set to full cold. That may be worth looking into before messing with restricting flow to the heater core. The heater core really shouldn't be significantly warming the cabin unless there's airflow across it.

If you do add ball valves to bypass the heater core, you'll want to add some restriction to the line returning to the lower radiator hose. When I've deleted the heater core in the past, it led to some overheating issues at low rpms. When the cooling system is at low flow and there's no restriction between the back of the block and the lower radiator hose, all your coolant bypasses the radiator and coolant temps start creeping up. As soon as rpms come up, flow increases, water passes through the radiator, and coolant temps drop back to normal... as long as you weren't stuck in traffic behind a wreck on a hot summer day in Florida and blow a headgasket first... but you'd be really stupid to do that.

The issue isn't so much hot air through the vents as it is heat in the footwell coming from the flow of hot coolant through heater core.

Did it to my NB2 years ago. Flow through the heater core heat soaks the whole underdash area and makes the vents blow warm. Because of lack of room with the turbo on the hot side, I routed the heater hoses behind the head to the passenger side. I used a two way valve to switch the flow to the heater core inlet between either the heater core or to a tee into the heater core outlet hose. I routed the outlet return through a long length of hose down across the front of the engine and to a tee into the radiator outlet hose. I have not had any problem with overheating and i live in Texas. Helped reduce the dash heat soak significantly. Easy to open the hood and quickly switch the valve position.

Since heat rises, the footwell heat is more likely coming from the exhaust that sits between the transmission and driver's right foot (LHD cars). Install heat shield on the body, there are videos and different approaches. You can find how-to videos on YouTube (Miata King has one he sells). The stick-on shield helped my MSM, I was also considering the type that attaches to the exhaust pipe with clamps and sits just off the pipe.

This is Germain

This is not a bypass, but rather a block. Do not do this unless you have another flow to allow the thermostat to see the heated water coming from the head. In my case, I have the turbo coolant feed at the re-route adaptor, so that works.

Glad I saw this. Springtime is time to close the valve.

DNM

Has anyone found good instructions on how ot adjust the heater blend door on the NC? ample info for earlier models, but I'm not finding good info for the NC. I've removed the glove box, but I'm not seeing the actuator cable.

Ah, an NC...I retract my statement about the exhaust. Pictures show it's opposite of NA/NB cars. It doesn't hurt to insulate the cabin from the exhaust heat. If the NC is a cable driven system, it should be as simple as popping the outer cable out of a clip and moving it forward or backwards slightly depending on if you want the cable to be looser, or tighter.