Wocha bin doin on your MG this week then?

I set the sensitivity up on my sensor to be a bit higher than usual as I wasn't entirely happy with whether it would work happily. The sensor, the same as TF135 uses (great minds etc.), has a sensitivity control, accessed by pulling the plain rear cover off the back. I have this mounted just above the seam on the header tank on the side closest to the car centre line using a military grade high modulus RTV which gets thrown my way when it has passed its ridiculously short shelf life. The fact it costs about £50 a tube has nothing to do with the shortness of the shelf life, I'm sure, but it seems to be fine when five years out of date. Ordinary bathroom stuff will work well enough. I power mine from fuse three which also runs the boot release.

Re the VW expansion tank as I understand it double skinning it is similar to baffling a petrol tank, the liquid still moves but the highs and lows are reduced.

Not my understanding at all. Baffling is not the same thing. Although others have used the VW tank, there is nothing wrong with the MG tank with an external sensor. nor the TF tank with an internal one. The shape of the tank is going to make bugger all difference as the liquid is going to move around anyway.
It ain't broke so why change something on the off chance that it will fix a non existent problem?

My knowledge of VW cooling systems is far from comprehensive; however I am unaware of a header tank which has an integral alarm. There are tanks which have contacts to monitor the current flowing through the coolant & any significant change would alert the external electronics; it is one of these which I have fitted. This was prompted by a cap & two original bottles failing in quick succession & for the price of an Ebayed VW tank, which had the reputation of being reliable, I considered it worth a punt .The pipework is compatible & easily adapted if one is adept at origami, although an additional bracket is required to fit it to the car. I suspect that it won’t blow off at the same pressure point as the original, I’ve been unable to track down that information,(although I didn’t really put my back into it) fortunately that point hasn’t been reached & thus further comment can’t be made.
I designed & built the original alarm circuit myself, which was fine & surprisingly immune to spurious slop signals, however a used Engine Watchdog TM4 turned up for which I gave £18-00. This particular Antipodean unit, which has now been superseded, monitors engine temperature, alarms on low oil pressure on top of the low coolant alarm. This would be highly recommended if the price were close to that which I paid, even three times the price, but as has been said it has been replaced in the range & when available was 150 Australian dollars. This is still cheap money for the savings it could make, especially fitted to a Ute thumping through the outback with mercury popping the thermometer bulb out at 120degree f.

I now await a pithy comment from Cobber & possibly Minimax. M

You have something that works. Good enough. People who maintain their cars carefully don't suffer the problems that the other 95% do.
I reckon that the best warning device is a coolant pressure loss alarm. The engine fails after the pressure cap dies or a hose pops. The pressure drops immediately, before any coolant is lost so you have more warning that something is amiss.

I used to build small steam locomotives & the boiler test was even more buttock clenching than an MOT. Building a copper & brass boiler is a significant investment & a failure is catastrophic, once up to & holding pressure is a relief, but once the test cock is open the pressure drops in an instant. A monitor within the water jacket would be of great help. You’ve got me thinking.

It doesn't need to be in the water jacket. The pressure will be the same in the small feed hose to the header tank

I used water jacket as a catch all & you are correct. In between fitting a new reversing light switch I’ve been looking at pressure sensors, one type might be useful; 0 to 5v analog, pressure up to quite a lot, the output into a comparator, with an alarm / indicator out. I’ve turned the tech side of the brain off now as I’ve a good book to dive into. M

Output into a window comparator and you could sense overpressure from a blowing hg as well

Certainly.

Airportable wrote:

especially fitted to a Ute thumping through the outback with mercury popping the thermometer bulb out at 120degree f. M

Do you mean a Ute like this one? I’ve already got one……it’s very nice!
It came with a low coolant alarm from Ford, and yes the alarm has saved the engine whilst it been getting the living shit thumped outta it! Once when the radiator had a shit haemorrhage, another when the water pump carked it, also when the thermostat had it’s last gasp and several times when coolant hoses and pipes gave up the ghost.The poor old Ute works bloody hard and gets precious little thanks for it’s trouble.The long suffering Ute gets loaded up with so much gear, it drags it’s arse up the road like a mongrel terrier with worms! And then to tow 2 1/2 tonnes of trailer.
It’s never been loved, but It’s has had plenty of sex…..every bastard has f#*ked it!

No finer illustration could be given & precisely what I had in mind, although the setting is somewhat tame. However I guess that if you were to pan through 180 degrees you might see a ‘roo filled scrub right up to the vanishing point. Or beyond if you are a flat earther. An eclipse would be interesting if it were a flat earth. M