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The V6 also returns a fair amount of coolant to the expansion tank which is'nt a problem, in fact it will help bleed air out the system as long as there is water in the tank to return to the engine.
that was my thinking on it ;)

if the engine needs coolant (and it does) it will get more circulating without this silly little valve.

and as you say it makes bleeding a lot easier too :)
 
The jiggle valve should not cause any issues, its a simple design, if its sticking someone has bent the brass outlet or not cleaned the system (gunk/mayo/radweld)

repeatedly squeezing the top rad hose should let you hear it rattling back and forward.

Technically, it isnt needed on the FL1, as there is an additional top tube on the radiator (at the highest point) allowing air to return to the coolant bottle.
With no ball bearing the coolant is directed through another short loop = hot coolant into the bottle and back to the coolant elbow, it will give quicker warm up times (when your heater is not being used)
IMHO you are better to blank it off completely on the 1.8 FL1 but leave it in place on other k-series cars which dont have a top rad bleed hose. eg MGF/TF where the jiggle valve is higher than the rad.
 
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The main problem with the K is it's cooling system and the fact the thermostat is in the wrong place. As it senses the water temp returning from the rad which has had any heat removed thus the opening is so delayed that the engine temp rises will above a sensible level before it opens. The upshot of this is the alloy has expanded by a larger degree than the elasopolimer seals can take, then the stat opens dumping cold water into an expanded almost overheated engine which suddenly shrinks the alloy back down. This cycle is repeated thousands of times until the seals fail. If the stat is moved to a more conventional place on the flow to the rad this will give a much faster response on warm up and also give a better general tempreture control which can only be a good thing. This coupled with the uprated parts should see an end to the K's reliability issues. The PRT stat is a sort of halfway house solution by allowing a small amount of water to circulate through the rad at higher rpm so reducing the thermal shock to the engine. Qed do a kit that will put the stat in the correct place to start with.
So is the thermostat in a better position in a V6?
 
Right thats pretty bad then ..so is a v6 stat plumbed after the radiator like the 1.8 ...sensing cooler temps and opening late

The V6 stat is Prt stat with bypass that is plumbed into the rad return. It's kind of a good system but it's got it's problems too. Most V6 cooling issues are water leak related rather than bad stat location. The top hose outlet and stat inlet are sealed to the block with an O ring in a slip joint. This can and does cause leakage problems over time and due to the stats location under the inlet manifolds in the V it's not easy to keep an eye on it. I generally remove the stat and replace the O rings at coolant change time which seams to improve the reliability of the system in general.
I believe that MGR chose to put the thermostats on the return to give a tighter control of engine temperature which is important in an all alloy wet liner engine.
 
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