I've noticed the heater in my 3 door isnt quite as toasty as it used to be and I suspect the matrix is the original.

How difficult is it to swap ?

I've done a Series 2 Turbo one and that was a proper mission.

I'm hoping the 3 Door one isnt the same.

 

No well i would say no the dash or bottom dash out two hose are the hardeest part in the engine bay unless you have a masive turbo in the way got my new one here for the rs500 then the saff to be done after that

 

Very easy, bit long winded job but easy.
Lower dash off both sides, undo pipes/ducting the matrix, undo bowdens(cables) by prising off and undo the little bracket holding the outer to the heater casing.
The bracket that holds the lower dash just below ash tray area can be a pain, I just grind out the two rivetts holding this, and replace afterwards with screws, this way you can just pull the whole heater box/matrix back.
Once heaterbox is out simply undo the two philips screws holding matrix to heater box.
When installing new one make sure you use the foam that should be supplied, applied to the sides and end of the matrix this tops air flowing around and not through the matrix.
When re installed be sure to adjust the heat control so that you are getting full travel on the flap pivot at the heater box, easy to do by adjusting the little bracket that holds the outer.
Insert a WAHLER 88C thermostat, my heater is roasty hot now with this stat.
tabetha

 

Cheers Tabetha !

Top answer as always !

Out of interest, now you have the 88 degree stat in there where does your dash temp gauge sit ?

I am sure I put an 88 degree stat in mine when we did the head gasket but not the temp gauge sits higher than the middle, half way up to the red.

 

I wouldn't worry about the temp gauge reading they are about as a politician!!
Mine can be anywhere from just into the norm(cold end) to just nudging the red, even though it is still at the correct temp, I put the laptop on it to check, I have a blue fan light so know when the fans come on, adn again the gauge reading is only very roughly accurate.
As an average it is a fraction below the centre point in the norm section.
I did get a noticeable increase in heat with a 88C stat, but no doubt some was due to the old one being sluggish.
Pisses me off that no one does a electronic thermostat like you can get on other engines, wahler make these, but won't respond to me emails for details, as this surely has to be the way to go.
tabetha