Lude Generation

air lock in the coolant?
faulty coolant thermostat?
something else?

the car runs smooth and vtec's fine though.

If your losing coolant then could be the dreaded heater matrix pipe leaking..

the one that goes from under the dizzy to the section underneath the intake mani?

if so, ive replaced mine before, was quite easy

Nope its the feed and return pipes for the heater matrix - they go through the firewall and are a bitch to get to
i think its is in @Merlin track lude thread somewhere
it can leak either side of the firewall so check for damp carpets on pass footwell etc
might not be this but could be if you are losing a bit of coolant and it smells a bit funky in the cabin

I would say either of the 2 options you suggested. In my old vectra the thermostat failed (fortunately open) so when driving the temp level was at normal but when sat still the temp would drop...even off the gauge. When it did this there was no heating.

Also, when my rx8 shat all of its coolant everywhere the gauge read anywhere from cold to on the limit hot (hadn't realised the loss of coolant as was driving). And that lost all cabin heating.

Back flush heater matrix with water and a compressor you will be surprised how much crap will come out

I would check for leaks and them come back.

haha this problem back in January was on Will's 4g and was sorted by topping up the coolant he's a div.

Drax wrote:he's a div

, I miss hearing comments like that. Brilliant.