Cooling system pressurised when cold!?

[Strides]

Hi All, hope you can help as this is puzzling me a bit:

1986 1.9 DG Petrol

Fitted a new header tank cap (Brickwerks) after the last one wasn't holding pressure at all. Cooling system has since been bled a couple of times via the radiator bleed screw.

I've been on a long run to Cornwall and back from Brighton and van has been running very slightly cooler than it's previous normal on the temp gauge so I was chuffed. While away though I noticed that the top up tank was filling up when hot but not drawing back to the header tank when cold. A big air bubble is sitting at the top of the header, so I siphoned coolant out the top up and poured it into the newly appeared air space in the header tank only to have the air bubble reappear when cap is on and engine is running.

With the system totally cold (24hrs since run) I opened the header tank cap to top it up again yesterday but as soon as I opened it the air was forced out of the cap and then the coolant started to overflow. Cap on and engine started the header level drops away again.

There are no visible signs of leakage anywhere (i've crawled all under it and inspected the rad) or cracks in the header to let air in / coolant out. Previously the van wasn't using any water. Any ideas why the air keeps appearing in the header and isn't being forced out via the cap into the top up tank, and why it's pressurised when stone cold?

Cheers.

[Aidan]

you did have the heater on when bleeding the system didn't you ? could be airlocked if not, but otherwise duff cap me thinks, it does happen occasionally

[Ian Hulley]

but otherwise duff cap me thinks, it does happen occasionally

My thoughts as well, had the same with 2 new GSF caps, solved with a Brickwerks one though.

Ian

[Strides]

Ah, good point about the heating! 1st time I bled the system it was on, but now you've said it I realise I forgot to switch it on the second time. I'll try again tonight. If that doesn't solve the issue I'll try a new cap.

Thanks for your replies.

[adstar22]

So, the coolant system SHOUDLN'T be presurised when cold... I just hope that my expansion tank (looks brand new and has a new cap on it) is just VERY full, as water was coming out when all I did was turn the top to undo it!

I think mine (also a 1.9 petrol wbx) has the same issue. I have already posted a problem where the temp gauge stays cold!

Are there any symptoms/checks for air in the system or do I have to bleed it anyway (something I am currently trying to avoid!)?!

[Ian Hulley]

I think mine (also a 1.9 petrol wbx) has the same issue. I have already posted a problem where the temp gauge stays cold!

Are there any symptoms/checks for air in the system or do I have to bleed it anyway (something I am currently trying to avoid!)?!

Does the heater get warm ? Sound's like an airlock. Bleeding it is easy, be carefull and follow the instructions on the wiki or Brickyard.

[adstar22]

My heater appears to be permanently hot! I suppose if I have to bleed the system.. it will be the right time to replace things like the thermostat and temp senders etc etc... just hoping to avoid a lengthy job.

[meridian911]

had exactly the same problem on mine afer replacing the coolant, temp senders & thermostat housing, solved it eventually by bleeding again (3rd time) and replacing another ! cap.
It seems to have gone away for now

[ermie571]

Honest, bleeding is a piece of cake. It seems scary the first time you do it.....but with an assistant is really is quite logical. Some lift the nose (or point uphill) others don't. We do because the van is parked on a hill!!!

anyways, take it slowly.....and keep doing it. it is the repeats that seem to do the trick for us. heating to hot on the sliders (don't need to run the fan though).

Keep the revs up while topping up - this is where we found the assistant was useful.- I sat holding the revs on 2000 while hubby topped up. When the expansion tank was just below peeing out all over the road, and the radiator was warm he cracked the bleed screw - it then blows bubbles or spits......when you can't get any more in, and there is no spitting from the rad screw, tighten screw back up, bung your darlick cap back on, and drop the revs. Switch off. Make sure top of tank has water in it that it can suck back if necessary. Allow to cool a while. Start again.

Good luck.


Em
xx

[adstar22]

Thanks for the support. To be honest IM not that daunted by the prospect of bleeding the system... I was able to do my old MR2 in 5 minutes... which isn;t bad for a 30 minute job. you kinda work out all the tricks and things.

What i am "concerned" about, is being a T25 virgin... finding the right things and not braking stuff. Resigned to doign it. Got the time set aside. Just need to buy the parts...any suggestions on best place for price and availability?

Was gonna give gsf a call...

[Ian Hulley]

Just be calm and methodical, these are not rocket science but are quirky. Don't go at it like a bull in a china shop and don't be too proud to ask, there's very little if anything that one (or most) of us have broken or replaced over the years

As for parts suppliers ... try Brickwerks, Simon fits what he stocks so he doesn't stock rubbish. JK can be OK for some things, GSF for others (except bearings).

Ian

[R0B]

if you were to fill in your profile so we know where you are.maybe a member close to you might offer to help you.

What i am "concerned" about, is being a T25 virgin... finding the right things and not braking stuff