thermostat

[ambivert]

OK... so on one hand I shouldn't replace any parts until I know the cause of the overheating... But on the other hand I am not going to be able to bleed the system - in order to see if it still overheats once I think I have fixed it - until it has a genuine thermostat and an expansion tank that doesn't leak!

Whilst I have the thermostat off I might as well take the pump off too and check it. I'll also flush the rad and all the pipes just to be sure there's no blockages anywhere.

Hopefully after all that, everything should be looking good or replaced, then I'll put it all back together and see what happens when I bleed it...

[ambivert]

One disc opens the return and one closes the recirc.

ah ha ! I've not clocked this. the thing I still dont get though is that when stat is closed both outlets in the top half are closed when open it allow coolant into the top chamber, What are the two discs you speak of? has any one got a stat and housiing picture?

Finally got the thermostat from VW, its nice...
[img:600:450]http://i-luv.info/stat.jpg[/img]

This is the housing:
[img:600:450]http://i-luv.info/housing_flow.jpg[/img]

This is how the housing opens into 2 pieces and the stat sits in the middle between them... the stat has a rubber ring which seals the join between the 2 bits. In this photo you can also see my old stat... butchered!
[img:600:450]http://i-luv.info/open.jpg[/img]

The housing has an upper and a lower chamber - joined by a port which the top end of the thermostat sits just underneath...
[img:600:450]http://i-luv.info/inside.jpg[/img]

The upper chamber has the radiator send, and two pipes coming FROM the engine. The lower chamber has the rad return and a pipe TO the engine (via the pump).

When the stat is cold, the upper and lower chambers are connected, as can be seen in the above pic. This means coolant FROM the engine can flow from the upper to the lower and then back TO the engine. The bottom part of the stat is also closed, which prevents coolant being pulled thru the rad, should any of it decide to leave the upper chamber via the rad send instead of thru the port into the lower chamber.

When the stat gets hot the top part of it moves upwards to plug the port between the upper and lower chambers. This now means coolant from the engine can ONLY leave the upper chamber via the rad send. The bottom part of the stat also opens to allow coolant from the rad return into the lower chamber and thus back to the engine.

Hope this is of help to someone

[Grun]

ambivert,
Brilliant images, and an excellent technical explanation.

Thank you so much for sharing them with us.

I hope your cooling system will now operate as designed.

Mike