They alert you when your coolant level drops below half way in the header tank giving advance warning of leaks, which with a modular engine like the MGFs can result in major damage.

As above. The jiggle valves are there to allow the air to escape during filling and then shut off the flow of coolant when the air has gone. They prevent the header tank from becoming part of the cooling circuit during warm up and so improve the warm up times by a fraction.

December 31, 2024 - The floating valve giggle system located at the engine close to the thermostat is intended to pass any entrained air to the expansion tank. The ball then floats in the coolant before sealing with minimal flow (if any) passing through it.

Flow to the head can be dramatically ... using a burring tool on a minidrill. The jiggle valves are there to allow trapped gases to vent back to the header tank....

"Any excess of coolant created by heat expansion is returned to the expansion tank via the bleed line. A jiggle valve fitted at the start of the bleed line, prevents pressure build-up in the expansion tank by regulating the amount of returning coolant.

October 4, 2010 - The jiggle valve allows air to bleed past it, but then shuts off the pipe when water tries to flow through it.

February 23, 2011 - It's actually a stainless steel ball trapped in a cage through which coolant returns to the block. As water is incompressible, it lifts the ball and stops flow through the small bore hose to the header tank.

Hi All, What does the 'Jiggle Valve' do? The heater matrix on my car seems to be running very cool at low revs 80-1200 (tick Over). If the car is rev'd

November 19, 2020 - It is designed to allow gases trapped in the top of the head to vent safely to the expansion tank. Removing it will simply allow coolant to constantly discharge from the head to the expansion tank.

I think the purpose of the particular jiggle valve nearest the water pump (not the one in the thermostat itself) is to vent air. Some will argue that the ball should be removed to stop it blocking up.

This serves to seal the outlet to stop too much coolant returning to the expansion tank but allow air to pass through. Mine was covered in greasy gunk and was sticking so it needed cleaning. On reassembly, the ball now rattles around in the housing quite happily.

Plus theres the question on how I connect the top hoses because I haven't got a 4 way T piece on my system, I have a strange hose that leads to the jiggle valve. ... It's my understanding that PRT is in the pipe that goes to the radiator removing one of the problems of very cold coolant being introduced into the head.

February 15, 2012 - hi there are 2 either end of the inlet manifold but the one towards the gearbopx is internal and doesnt stick the on toward the cam belt end does get stuck sometimes, it has a small bore pipe attached to it, to do it quickly this pipe can be blown down but if you suck you shouldnt be able to do it as you can see from the pic the pipe that goes down past the oil filler is the pipe to the jiggle vave ... Hi are you on about the red pipe that goes down the one that joins to the t piece going to the header tank??? If so I have took that off and can't blow and can't suck??? So I would say my balls have got stuck lol what is the best way to do this??? ... I will have a look today and check the valve down near the oil filter?

January 27, 2016 - Following a HGF repair on my MGTF VVC 160 I was told by the mechanic that he had removed the inlet manifold jiggle valve. When asked why, he said that is what they do???? 2000 miles on the car is running ok. I have noticed that the temp gauge goes to normal after about 1 mile, though the heater does not get warm until 3 miles. Once hot the heater stays hot (while set to hot) with no fluctuations. This situation is always the same on start of a run. I bled the coolant system several times at the three points I am aware of.

Failure to ensure that all the air is bleed from the cooling system will allow pockets of air to block the flow of coolant - which can lead to localised overheating and thus failure of the head gasket.

Hi first post on this board and hoping someone can help me. My car, 99 mgf, suffered hgf recently and i carried out the repair work myself and have since had 500 trouble free miles with a seady

November 4, 2013 - As to the OPs question, why would you want to ditch the jiggle valve? The only failing I have heard of is the jiggle valve seizing in the closed position, so removing it would only put you in the worst position anyway. The only reason I can think of with MG removing it was it made the system a couple of pence cheaper and possibly wasn't needed in the new configuration.

July 11, 2016 - I ended up on a tow truck The recovery guy said it's HGF but to be fair he didn't look at it. I'm hoping it's just an overheat. If I put water in it was fine...and the oil temp dropped to normal...for the 1/2 mile it lasted until running out of water again. Anyway, I'm sorting the hose issue and have pulled the jiggle valve of the thin return pipe.