Re: Still losing coolant!
Right, I'll start with basics..
Coolant can either
Leak out externally, to the floor etc.
Leak into the oil galleries.
Leak into the bores.
That's it. There is no other magical place it goes.
It's either leaking out, being burnt, or mixing with oil.
Next. Any decent coolant will dry up and partially close a small leak. I'm not talking about cheap crap, the super long life stuff will literally crust up, and all but stop the leak. Would be chunks of it behind the cambelt cover for example if it was the water pump. To the extent it rarely hits the floor. You can pick lumps of it off.
Again, cheap coolant will leave dry residue stains, but generally leaks to the the floor.
Coolant systems are pressurised. Even with pure water, they won't boil at 100. With coolant, it's even higher.
If the thermostat is stuck, the car will overheat. It may take longer on diesel's, but with not external cooling. It will overheat.
The coolant is not boiling off, it's just getting hotter than the car likes.
Any steam can only vent through the pressure cap on either the radiator, or expansion tank. If it was venting through a leak, it wouldn't overheat in the same way, as it would dump it's coolant before it leaked steam.
Misted up windows do not mean a heater matrix fault. They can. But much more likely there is a faulty door seal, membrane, bonding or seal on glass etc.
Just because the carpet feels dry, doesn't meant the deadening under it is.
It's usually a foamy material, which acts like a sponge.
With out taking carpets out, it would never dry out fully, not any time soon anyway. Especially if the leak source hasn't been fixed.
I've been in the trade for 14 years, and I can count the matrix's I've changed on one hand.
I can't say the same for the amount of door seals, membranes, etc. Not even on all my fingers and toes would I come close!