cooling system pressurising.

milko · Unread post by **milko** » 05 Apr 2008, 22:24

hi. i've got a 1995 xantia t.d that i've just had the joy of putting a heater matrix in, now the cooling system is pressurising. when the cars left ticking over to warm up then left to cool i can take the header tank cap off all is fine. if i take the car for a drive temp gauge is fine, if i leave to cool down over night and take cap off the coolant sprays out with force. any ideas please?

Unread post by **CitroJim** » 05 Apr 2008, 22:41

Well done on swapping a matrix

I have that pleasure to come soon!

I don't think you have a problem

If the temperature is fine on a hard run, the fans generally are not running in normal driving, you're not loosing coolant (except when you release the cap), the rad is nice and hot all the way across and the heater is working, things are more than likely OK.

What is possibly happening, now the system is so well sealed due to the new matrix, is that a nice depression is forming in the header tank as the system cools. When you release the cap, the depression is violently equalised. My Activa has a tendency to do this. In fact the depression can hold the cap on so tightly at times it is actually hard to remove! I have also observed the same on my 2.1 despite a slightly poorly matrix.

Also, the header tank is best not filled to the brim. In fact it finds its own level soon enough and this is normally right at the bottom of the sight gauge when cold. Check the discharge tube is clear, allowing excess coolant to escape as necessary.

It may be that the system is over-pressurising a little because of a slightly duff cap. It might not be a bad idea to replace it. Also, give the entire cooling system another good bleed to ensure all air is out.

citronut · Unread post by **citronut** » 06 Apr 2008, 01:20

run the engine with the cap off till the top hose becomes hot, now top up the coolant but not right to the top, put the cap back on and run engine till the fans cut in, once they cut out you remove the cap gingerly you now should only get a very slight release of presure, if any more than that you have a problem
regards malcolm

DickieG · Unread post by **DickieG** » 06 Apr 2008, 07:56

citronut wrote:run the engine with the cap off till the top hose becomes hot, now top up the coolant but not right to the top, put the cap back on and run engine till the fans cut in, once they cut out you remove the cap gingerly you now should only get a very slight release of presure, if any more than that you have a problem
regards malcolm

Is that correct Malcolm? Opening the cap with the engine at running temperature, I've always found that the coolant overspills anyway, hence all the warnings on the cap and in handbooks.

Unread post by **Peter.N.** » 06 Apr 2008, 08:41

If you fill them to the top they will always expel some coolant and will usually settle just below the 'normal' mark, but if it goes on blowing water out (through the overflow) to the point that the reservoir is empty, I'm afraid you probably have a head gasket problem.

simoncanfer · Unread post by **simoncanfer** » 06 Apr 2008, 11:38

Respect! A DIY matrix change!

I am not familiar with the exact setup on the xantia- but on my ZX I diagnosed a head gasket failure early on because I could see bubbles in the system. On the ZX there is a narrow thermostat bypass hose that feeds to a pipe within the header tank (it's actually part of the rad.) I could see the squirt of water from that pipe had bubbles in it.

When you bled the system after the matrix change, did you use the elevated coolant "header" and run the system "open" until thermostat opened etc? I believe this is the only way to properly bleed it.

Simon

Clogzz · Unread post by **Clogzz** » 06 Apr 2008, 14:10

the coolant sprays out with force

Sign of air in the system. ^

No need for an elevated header if you open the vent on the outlet of the matrix.
This vent is the highest one, and all the air will finish up there.

citronut · Unread post by **citronut** » 06 Apr 2008, 14:41

i agree with Clogzz, as i never use any aid to bleed any of the citroens, and i never have a problem whast so ever, i find after all the bleeding still run the engine with the cap removed till the top hose becomes hot (thermostate open), then top system up to half way up the header tank

(if you still have the sleave in the neck of tank the coolant should be at the bottom of the slot)

now reffit cap continue running engine till the fans cut in, when they cut out gently remove cap and you should not get much presure escape, if you do i belive you have a problem
regards malcolm

Unread post by **CitroJim** » 06 Apr 2008, 15:18

I quite agree Malcolm, I have always used exactly the same method as you with never a problem. It even works if the bleed valve is not available for use for whatever reason.

Milko wrote:if i leave to cool down over night and take cap off the coolant sprays out with force.

Is the above a result of a depression as I initially thought (because my Activa does it and I know her head is perfect) or as a result of trapped air and pressure?

Milko, we need more information. Is it loosing coolant whilst being driven, does it overheat under any circumstances and most importantly, if you run it with the expansion cap off, can you see any regular streams of small bubbles in the coolant?

Was it OK before the matrix change? I ask as it can be a devil sometimes to get the full quantity of coolant back in due to airlocks and they can be very persistent.

deian · Unread post by **deian** » 06 Apr 2008, 16:50

Did you put the heater slider to hot inside the car when you emptied the coolant and refill, so when the water will access the matrix too, not just circulate around the engine?
If not then the new matrix is empty and the water pump is also pumping air around, although I can't see this building up pressure as it would need pressure from somewhere. Is the water level ok and staying ok?

My experiences of a high coolant pressure was when i had a blown headgasket on a pug 106d. But the pressure was high enough to blow the cap open to release the pressure. This meant there was a split in the headgasket so the exhaust from the cylinder was going into the water system hence the pressure, it was also getting increasingly harder to start because of poor compression. The classis mayonaise you get in the header tank is when a head gaasket is split near an oil channel so oil gets into the water not exhuast (as was my case).

I don't think this is the case with yours though.

milko · Unread post by **milko** » 06 Apr 2008, 17:14

hi again. thank for all your replys, you've all been very helpfull. i've had a day messing about and found the small pipe from the header tank to the bleed hole on top of engine was block, stopping me from bleeding the system properly. thanks again for you help and good luck with your matrix change citrojim.

citronut · Unread post by **citronut** » 06 Apr 2008, 17:54

Dei

i belive XANTs dont have any valve in the matrix circuit as the heat is just redirected out of the car when hot is switched off, so there is nout to stop the coolant flowing right through the system except the thermostate when shut
regards malcolm