Coolant pressure

MikeT · Unread post by **MikeT** » 23 Apr 2008, 23:14

Issue number 687

The clues:
The coolant is under more pressure than my last Xantia. It also sounds like it's mildly venting through the pressure relief valve cap. The temp sender generally reads 70degrees while driving above 20/30mph. Left to idle it will slowly move up to about 89 and if pushed, go to about 99 where the fan brings it straight down again. The driver's footwell is damp-sodden underneath. While the radiator is new and the cabin heating works. Any ideas what it could be, what to check for?

steelcityuk · Unread post by **steelcityuk** » 23 Apr 2008, 23:49

Similar problems to my XM. The head had gone (more likely to be the gasket on a Xantia) and 'popped' the heater matrix. Easiest way to check would be a leakdown test.

Steve.

MikeT · Unread post by **MikeT** » 24 Apr 2008, 10:12

So assuming it's not a weak coolant pressure relief valve, the coolant is being over-pressurised by what.....the cylinder gases?

Would there be other indicators I can check that doesn't involve paying someone?

Unread post by **RichardW** » 24 Apr 2008, 11:03

The cap is the pressure relief valve. Normally the coolant is only pressurised by the water and gas expanding as it heats up. However, if you have a HG leak then exhaust gas can escape into the cooling system causing it to pressurise till the relie valve (ie cap) lifts and lets the gas out. Checks:

With engine cold feel top hose and see if it is hard, then remove the cap and see if it hisses.
Refit cap and start the engine, run for 1 minute, stop and remove the cap - see if it hisses.
Re-start engine (cap off) and look in header tank for lots of small bubbles rising.

Answer yes to one or more of these and it's pretty sure time to decapitate it...

MikeT · Unread post by **MikeT** » 24 Apr 2008, 12:44

Ok, here's the results....

Stone cold engine, top hose soft - no escaping pressure when cap removed.

Start and run engine for one minute on idle. Cap removal hisses and light vapour visible.

Restart engine, no bubbles though vapour still wafting. I added some deionised water to bring the level up into the light and still no bubbles for a minute or two so revved up to about 1500rpm and a white froth began to form on the surface, eventually turning the all visible coolant into a milky white colour. Releasing the revs caused install overspill and lots of big bubbles appeared.

Is that 100% confirmation of head gasket failure?

deian · Unread post by **deian** » 24 Apr 2008, 12:51

Exhaust from the engine is leaking into the coolant hence the build up of pressure, i've seen this before on my old pug 106 1.4d, but mine was getting harder to start too (loss of pressure in the cylinders), are you having that problem too?

Unread post by **CitroJim** » 24 Apr 2008, 13:33

MikeT wrote:Is that 100% confirmation of head gasket failure?

Unfortunately, pretty conclusively yes Mike

I guess you have now made your decision over the future of the car...

MikeT · Unread post by **MikeT** » 24 Apr 2008, 14:32

Hi deian, good to see you haven't left yet

I think I can detect a whiff of exhaust from the coolant - tried my new stethascope today and it's gurgling like a hungry rhino in there but I can't say it's causing starting problems.

Hi Jim, so I can add head gasket failure to the list then

Time to update my blog.

p.s. As it has a new radiator I'm paranoid about the cooling system not being sufficiently protected from corrosion - should I drain and refill or is there a better method/additive while I decide on my next course of action?

citronut · Unread post by **citronut** » 24 Apr 2008, 18:00

i would spend a bit of time bleeding the system, take out the plug in the top left corner of the rad, top up coolant till it comes out of the plug point and stops sinking, replace the plug now remove both the bleed valve caps, keep topping up till coolant comes out of these, if it dosnt just run engine till it dose then replace both the bleed caps, now run engine till fans cut in wait for the fans to cut back out, now gently remove header tank cap, if the system is ok you should only get a very slight hiss,

after saying all of that if you get some one to crank the engine over with tank cap off and engine stone cold, if you get any coolant expantion you have got a head gasket gone
regards malcolm

MikeT · Unread post by **MikeT** » 24 Apr 2008, 18:12

Thanks Malcolm, though I'm inclined to drain and ditch the existing coolant as it's unknown to me so will go for a complete refill. I didn't realise there was a top plug on the radiator. I know where one bleed valve is (eh Jim?

) so I'll have to revise my Haynes for the second. It's not on the firewall by the matrix in/outlets is it?

citronut · Unread post by **citronut** » 24 Apr 2008, 18:19

i persanoly dont use the bleed valve at the bulk head for the heater matrix and never have any trouble bleeding any of the citro/pug engines, the plug i mentioned when looking under the bonnet its at the top right corner of the rad
regards malcolm

MikeT · Unread post by **MikeT** » 24 Apr 2008, 18:21

Sorry, I thought you meant there were two bleed caps in addition to the plug. I know one is on a three-way hose connector on the top engine mount, where is the other bleed cap?

Unread post by **CitroJim** » 24 Apr 2008, 20:53

Mike, as you know, I use the same method to bleed as Malcolm..

The 1.9TD only has the one bleed valve on the three-way junction. Some engine variants have a bleed valve on the head and anothher on one of the heater hoses, up high near where the hose enters the matrix connector block. Others, like the 2.1TD, have no bleed valves as the header tank is up on the bulkhead and therefore is higher than anything else.

You can also bleed the TD, in the case of stubborn air, by removing the small hose on the LH (as you look at it) side of the head. It's worth noting that this little pipe and it's spigot on the head sometimes blocks if coolant changes have been neglected. Worth a check!

admiral51 · Unread post by **admiral51** » 24 Apr 2008, 21:34

Hi Mike
sorry to hear you have found a big problem

have a look in here may give you a cheap option if it does indeed turn out to be the HG

Colin

MikeT · Unread post by **MikeT** » 25 Apr 2008, 00:13

I'll do that refill and bleed first opportunity after checking that spigot for blockages. The head gasket repair in a bottle has me undecided, tempting as it sounds.

I've got the offer of a coolant gas test which will diagnose two levels of failure but I would have to drive the car and don't think it's wise, despite all the precautions I'd take.