Cooling system running pressure.

[Mogmike]

I've just had the dreaded head gasket failure and had the head skimmed etc. I want to fit a header tank with a level sensor to keep an easy eye on coolant level. I have the untouched 1.8 petrol engine. The current expansion tank cap has 140 embossed on it. I have a spare VW golf expansion tank which has a built in level sensor. The cap on it has no marking. Does anyone know if the cooling system on my Rover is a sealed system that just overflows when getting too hot or is the 140 cap designed to release coolant if the pressure is more than 140..?
What I'd like do is fit the VW tank and run as a sealed cooling system with the level sensor.. Is that feasible or am I being foolish to think that way..?

[SD1too]

Originally Posted by Mogmike

... is the 140 cap designed to release coolant if the pressure is more than 140..?

Yes.

Simon

[rrobson]

140kpa works out at about 20psi. Running pressure should be around 1 atmosphere or 14.5psi. So provided the Vw tank has a similar design in that the cap has an internal pressure relief it will likely be somewhere near. You could always pressurise it with a foot pump and see what it blows at.
It’ll just be space and plumbing that will cause issue, then the additional circuitry to monitor the level.

[T-Cut]

Originally Posted by rrobson

1Running pressure should be around 1 atmosphere or 14.5psi.

Here's the vapour pressure/temperature diagram, which gives all the data according to the antifreeze concentration (RHS).

So, if you know the running temperature and your coolant mix, you find the runnng pressure. The blue and red lines indicate the pressure cap release conditions of the now obsolete 100KPa pressure cap and the standard 140KPa cap. Coolant 50% antifreeze/water mixture.



These data are theoretical, so the pressure values are likely to be a bit higher in a real life engine.

TC

[Mogmike]

Many thanks..SD1too, rrobson and T- Cut for responding.. Really helpful comments and diagram.
I'll now track down the VW golf cookant running pressure.. The VW expansion tank cap definitely has a release facility but there's no marking.
I've checked I can fit it in..so fingers crossed it's game on.. I'll post what I end up finding out and doing.. Thanks again..👍

[WillyHeckaslike]

A couple of members that I know of have used a VW Polo expansion tank in lieu of the oem tank. To obtain a low level warning they have connected its low level sensor to the circuit which provides a warning for low fluid level in the windscreen washer bottle. But I'm not sure if all of our cars are fitted with the appropriate wiring, you will have to check.

There might also be a way of connecting a low level coolant sensor to the car's existing wiring without using the washer bottle circuit mentioned above. Member Lovel (Gary) has posted some info on this.

[T-Cut]

Originally Posted by WillyHeckaslike

A couple of members that I know of have used a VW Polo expansion tank in lieu of the oem tank.

There's at least one archived thread discussing how this was done. I remember one mod had the header tank mounted on the firewall.

To obtain a low level warning they have connected its low level sensor to the circuit which provides a warning for low fluid level in the windscreen washer bottle. But I'm not sure if all of our cars are fitted with the appropriate wiring, you will have to check.

There's a warning icon available on the diesel instrument pack. See the Handbook.


EDIT



TC