I've got an Evo6 GSR

I'm finding the underdash temperature / footwell temps to be extremely hot - like the heater is on highest temp and full bore.

This happens within about 10mins of the car getting up to temp with normal driving.

Points to note:

1. All AC removed, including the condenser. OEM RS grommets used on firewall in all the holes.
2. Firewall sound deadening has been reinstalled per factory GSR.
3. The fan box has had the condenser hole (where the pipes ran out to the firewall) plastic welded closed.
4. I am still running the climate control style dash controls, not the RS style.
   
5. The heater hoses to the firewall are connected per factory for use in winter when I do actually need a heater.
   
6. I've fitted a new (OEM) thermostat this week which hasn't changed anything.
   
   Also pulled half the dash apart. The hot area under the dash is definitely the big white box - namely the heater box.

Again my suspicion is the heater core is getting continually filled with engine bay temp hot water, which is being blown around the cabin.

Feels like 40+deg C inside my car, with recirc on, the fan off, blowing angle to the windshield and temp control down to 17deg (c).

Next thoughts are:

Re drain the radiator and loop the heater hoses together on the firewall and on the engine. I don't need a heater in NZ.

Some have mentioned a control valve (HVAC), relay or fuse however I'm not sure where that is.

 

i have the same dilemma in my 6 if you ever find an answer to this i would love to kno as well

 

My 8 is the same way although not as bad as you describe. There is no water control valve like some cars have so, yes, hot water is running through the heater core all of the time.

I bought a new blend door which I never installed. The door isn't a flapper, it slides back and forth and is a loose fit. When the hot side is closed off hot air will still leak through. On a cool day with cold air dialled in it soon is warm in the cabin. So, I run the AC.

I've thought of installing behind the intake a brass valve from a hardware store plumbing department. The valves that are used on cars are either a rusty mess or plastic.

 

I like the brass valve idea - spliced into the heater inlet hose - I'd have it 'off' during summer and on again during winter.

Unfortunately after working on this all last night I'm none the wiser and still have the issue.

All solenoids/actuator arms work on the heater box, and the fan speed has all speeds (low-high).

 

Isn't this just as simple as the heater temperature was on full heat when you removed a bunch of the A/C components? So effectively it's like the tap is on all the time pumping the hot coolant into the cabin and back out.

I roughly remember too the climate control unit on the VI defaults to max height when the power is reset to it.

 

Thanks - yes you're right re the high heat reset, but turning the dial back down stops this happening.

Unfortunately Evo's don't use a mechanical heater valve on the thermostat housing like many other cars do, so hot water is always passing through under the dash.

When driving the car the controls are set to:

Recirc
Fresh air at the windscreen
Set to 17deg C (low)
Fan speed OFF

Therefore the heater core shouldn't be holding heat as the water should just pass through. But it seems to be picking up the inbound fresh air and heating it up.

If I was loosing coolant I could understand a blocked heater core but car temp gauge is stable and I'm not loosing coolant.

My next fix will be to drain the coolant again and loop the heater hoses so no hot water from the radiator is running through the core.

 

let us know if u fix this! gl! free bump

 

i just came back from a long road trip and i semi figured out my hot evo 6 cabin was caused by the extremely hot transmission tunnel especially on the passenger side where the downpipe/exhaust pipe is tucked right up by the tunnel figured ill start by heat wrapping the whole pipe maybe even some heat reflect tape along the tunnel and see how much that helps. still havent quite figured out why the drivers side footwell gets so hot but it definetly heats up the panel right under the steering wheel im thinkin of putting some heat insulation under there to cover the wires nest tucked up under there will post on here if any of those work on the heat issues