I have got a 1.8 zetec with a polo radiator, can anyone please tell me if it should be pressurised. i have had it up to temp but when i take cap off nothing happens.
thanks
Rick

yes. cooling systems need to form pressure as to raise the boiling temperature of water. to much is also bad

there seems to be no pressure at all in mine, and i have no leaks, water or air. so how do i pressurise?

The first thing that springs to mind is the pressure cap on your header tank.

Water/coolant based systems will run up to 15 psi of pressure so its quite obvious when you loosen the cap. Obviously be aware of the dangers of hot pressurised coolant.

When you say that it is coming up to temp, what is the actual temp? 90 degrees or so? If so you will propably not generate any pressure unless you go above 100 degrees.

to bleed the air system do i have to realy need to boil the system up then? i got up to temp at around 95 and switched off

quote:

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Originally posted by ricklawn
to bleed the air system do i have to realy need to boil the system up then? i got up to temp at around 95 and switched off

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You almost certainly have a faulty pressure cap. The system will be starting to pressurise as soon as it starts to warm up. It should certainly have pressure in it at 95 degrees.
Try a different cap. And beware of the dangers of hot pressurised coolant.
Geoff.

i turned it off when it got upto 95ish as the fan hadn't come on so also need to check wires. the expantion bottle is plastic type with snug fitting plastic cap.

Is it a new plastic cap?

old

Get a new one before pulling the rest apart they do fail

cheers onzarob, will do

So is there a pressure cap on the radiator itself, or is the pressure cap on the header tank? The "snug fitting cap" you describe does not sound like a pressure cap. Where did you get the header tank from. What vehicle is it from? It sounds like you may not actually have a pressure cap on your system at all, unless it is on the radiator itself.
The fan probably won't cut in till the temp goes near or over 100, which could be accompanied by lots of steam if you are running un-pressurised.
It is a good idea to have a manual switch for the fan as well as the temperature activated one.
Geoff.

The cap on my Audi and my previous Golf MK1 is a snug fitting cap and I've seen the header tanks used on plenty locosts.

I do feel that the newer caps add to the confusion as they do look like a seal unit, but they are still pressure release caps.

But is the expansion bottle cap a pressure cap ?

Older systems had pressure cap on radiator and expansion bottle was just an overflow and un pressurised.

Newer systems have pressure cap on the expansion bottle. You might have older type expansion bottle which with Polo rad means you have no pressure cap at all and hence no pressure.

Easy enough to find out. The plastic ones don't have an exterior outlet like radiator caps, but they do vent inside the cap. Mine has four vertical grooves on the inside of the cap. When pressure builds above a certain point a spring compresses and alows the vapour to vent via the grooves.