Thermostat not opening

My car is overheating temp light comes on.
The fan is working if a cross the wires. Coolant looks ok.
After going for a run I found the top radiator hose roasting but the bottom one is cold. [No circulation]
Does this mean thermostat is not opening and needs replaced?
How easy is this?
thanks
cc

really easy - two bolts and the housing is off - order a new seal when you order the thermostat. You could replace the housing as well - couple of quid

Here's a diagram of the complete system.  It is a closed loop.

Refill with 50/50 G12 mixture (pink stuff from VAG) but don't mix with other glycol apparently or so another post advised on this topic.

MP

Thanks mate.
Looks a bit scary but I've got a manual somewhere.
cheers

it is an easy job to change the thermo, but what happens if you change the thermo twice, flush the engine rad and matrix and made sure there are no air locks in the system, and still the bottom hose is cold ???
is this the water pump gone ? surely if the fan belt is turning the pulley then it should rotate the pump inside, as it is a fixed shaft  :dontknow:
anyone any ideas

Has it actually over heated, i.e. boiled up and thrown steam and water out?

When cold, remove the expansion bottle cap, start engine and rev it up, you should see water being squirted out of the long thin hose 14 on the diagram into the bottle. If so the pump is working OK.

Its not unknown for the water light to lie and flash at random. Does it ever do it when you know the water is cold? It also goes off if water level is low. The switch in the expansion bottle or its connector might be U/S.

only recently got started on this little project and this has a top fill radiator, although there is a redundent expansion tank in there, which means the rad has been replaced at some stage, but if i leave the cap off the rad i cant see the water being pumped through. having a different rad in there wouldnt be the problem would it ?

Does the now redunant expansion bottle have the water level switch??? If it does and there is no water in it it will make the light flash all the time. :dontknow:

Does the car actually over heat, ie boil up and loose water???

Does the now redunant expansion bottle have the water level switch??? If it does and there is no water in it it will make the light flash all the time.  

Does the car actually over heat, ie boil up and loose water???

there is water still in the redundent water tank, so have no light flashing and yes it overheats if run for a while, with steam coming out of the rad filler

I took the thermostat out and tried flushing the system before replacing stat, but water pours out bottom of pump (all hoses etc connected tight).

I can't remove water pump to see what's going on though according to the manual I've removed all 4 bolts. Any clues what's happening. I've tried gentle persuasion.

well got around to changing the water pump today on the 1.5gl ( as well as the 4 bolts there is another 10 mm nut and bolt going thru the pulley cover which has to be removed ) refilled it, still the water is not circulating, the heater is blowing hot air, but the bottom hose is still cold and water is not coming thru the top hose.
 
the expansion tank is not used as such, as it contains the windscreen wash
dont understand it as the connectors at the rear of tank are connected correct for the screen wash, but it has a hose that looks like it should connect to the rad, but the rad fitted is a top fill  :dontknow:
its been flushed til water runs clear, everything has been correctly fitted, so whats going on  :dontknow:
anyone  :cry: