There's no fail safe or anything slightly sophisticated about these stats. They have a simple sealed wax capsule containing a piston. The wax melts, expands and pushes the piston out. The valve is attached to the piston. When things cool down, the return spring ensures proper return and closure of the valve. How this device can pass coolant when below the wax setting I don't know.

What's needed is someone to check a 'failed' stat in water to see what happens to it. Does it open at too low a temperature? If so, my understanding of paraffin waxes is incomplete.

TC

"thermostat was bejiggered, and had to be replaced (easy jobs on those cars). It ALWAYS stuck open . My experience anyway. Are modern stats made different ?"

OH now then on second (and many more !) thoughts, the stat always APPEARED to be open . That was before this long discussion. Maybe the stat actually opened at a very much lower temperature than it should, due to loss of wax/water ingress due to overheating. I cant work out the results of this though , only observe that the stat didnt work properly.

All I know is that the wax stats were sold in the 60's on their property of failing safe (open) and that as the M75' stat starts to fail it means the engine runs cooler. The old style bellows type, when the bellow failed would fail to open and the car would boil up.

I will test a couple of duff stats in hot water............ when I get time!!
I've always assumed it's simply a case of the spring weakening with age.

Fitting another tomorrow & another on Thurs so another full day together with posting lots of parcels.

Jules,
That sounds great. It will be very interesting to really know what is happening to the stats.
So I assume that you will be testing some faulty stats with a new one as comparison.
Will there be a way of testing the spring tension?
Matt

Stats
 

Matt, I have tested my brand new,unfitted, stat three times and it opens at an indicated 91 C. increasing the return spring pressure made no difference as TC indicated. JULES is the key to more knowledge on this problem as he is going to check the opening temps on failed stats. Since
he has never found one stuck open or seized up then, logically, the only problem must be that the stat is opening at a lower temperature?
With regard to blanking off the radiator, it is not as simple as on most cars because the intercooler and the air con matrix,and the 2 speed fan resistor, should not be blanked off
so has anyone given thought as to the best way to do this?

I guess we're getting into brainstorming time. Maybe a flow control orifice inserted in the hose from the cylinder head? If the flow rate to the radiator was slowed down, the running temperature would increase. I could sell it on eBay.

TC

Of course the size of the orifice would need to vary, to take account of the waste energy needing to be disposed of - perhaps you could call it a thermostat :D

Mmm
And when engine needs max cooling on hot day it would boil over with a restricter in there.

Any other ideas cos the 88 deg setup is still fine IMHO!

Sort of like a stop-****? I'll get down to B&Q in the morning.:D Seriously though, nice idea.

Air gets to the AC condenser and the fan resistor through the main grille. So maybe a sliding air vent to the under-bumper grille? Similar idea to the air vents used on blocked-off chimney breasts.

Ooooh, look! My genuine name for a piece of plumbing equipment has been moderated. For anyone who can't guess what the missing word is, it starts with c and has an o another c and a k in it. But not necessarily in that order. Funny breasts wasn't moderated.