Coolant pressure
Moderator: RichardW
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Coolant pressure
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?
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?
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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...
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...
Richard W
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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?
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?
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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?
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?
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
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
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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?
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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!
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!
Jim
Runner, cyclist, time triallist, duathlete, Citroen AX fan and the CCC Citroenian 'From A to Z' Columnist...
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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
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
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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.
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.