C5 Coolant Loss

Why do that? It doesn't sound like normal practice, to me; I'm not familiar with the C5 though.

Are you sure it isn't water-vapour? Air would be unlikely. If it is water-vapour then you are letting water out of of the system, which would otherwise turn back into water as it cooled and the pressure in the system returns to 'atmospheric'.

Releasing pressure from the hot system would be expected to result in liquid being drawn in from the header-tank (which is probably still at 'working pressure'), on any liquid-cooled car I've lifted the bonnet on.

Does the water-level drop overnight if you don't open any valves while the engine is hot?

The pressure-cap is meant to release excess pressure so it will sometimes 'hiss'. I think that's normal, as far as it goes. Having a pressure-cap that opens at too low a pressure would probably lose coolant quicker than normal - but don't fit a pressure-cap with a higher rating than the handbook specifies!

As far as the loss of coolant you actually detect for yourself is concerned, I would suspect you, releasing pressure from the system while it's hot, for a start ;))

In the old days, radiator hoses could become porous and lose liquid slowly and invisibly (one usually discovered the faulty hose when it ruptured spectacularly while the car was being driven, if the hoses weren't all replaced at the first sign of trouble). There could also be tiny leaks at the places where the hoses are fixed onto the metal parts. A brief 'pressure test' might not show such things. I've even encountered a radiator with tiny leaks where metal had eroded away or stones had damaged the tubes, but that was in the '70s on a very old and neglected car with many worse faults than that.

If the warning light is giving false warnings when the engine is in fact not over-heating or running low on coolant, then the detector(s) controlling that warning light would seem to be worth checking.

Of course, I could be barking up entirely the wrong tree.

Whiskers ( snipped-for-privacy@operamail.com) gurgled happily, sounding much like they were saying :

The technical term is "Steam"...

There shouldn't BE any steam in the system if it's running at normal temp (about 80deg), and correctly pressurised.

Indeed.

No. The bleed screws should only release water. There's definitely air getting in there from somewhere, and that somewhere is where the water's going...

My suspicion is that the head's cracked, the block's gone porous, or some other internal water leak.

When the head gasket was replaced was it just swapped or was the head checked for flatness (warp) and crack tested - if not you could still have problems in that area. :~(

Indeed, many modern cooling systems need a 'head' of water to bleed air out of the system when being filled, opening a bleed screw without that 'head' could well induce air into the system rather than remove it...

If you are suggesting that there is *steam* in the system then there should not be steam in the system - OTOH if you are suggesting that by venting a pressurised system to atmosphere the water is turning to steam after release then you might well have a point!

That would be normal, even if the head gasket is blowing.

Agreed; but releasing the pressure by opening the valve will cause the water to evaporate. (You won't necessarily see 'clouds of steam' if the air around the valve is warm and the pressure is enough to disperse the vapour before it cools).

Any air getting in would have to be at a higher pressure than the liquid in the cooling system, wouldn't it? If that is happening then the cooling system will be getting over-pressured and the pressure-valve will be operating to release the surplus, and that would be where the coolant is escaping. But how is air getting pumped in?

Replacing the head gasket should have revealed anything as drastic as that, shouldn't it?

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The latter scenario is the most likely, I think. If "steam" is getting trapped anywhere in the cooling system then there is a serious blockage somewhere and the coolant is not able to circulate - and I'm surprised the engine is still in one piece.

I used the term "water-vapour" because in colloquial usage, "steam" usually implies visible clouds of condensing water rather than water in its gaseous state as such - which might easily pass for "air".

Whiskers ( snipped-for-privacy@operamail.com) gurgled happily, sounding much like they were saying :

Combustion chambers would be an obvious source...

Not if it was just swapped over.

Which should be attended to without any delay. Certainly no more high-speed journeys in the meantime!

Wouldn't some sort of check be part of the job, if it were done professionally? A suspect gasket is itself a sign of other possible problems either as a result of the gasket failing, or causing the failure, surely?

Thanks for the input.

Releasing the blue valve is the latest attempt to fix this 6 week old problem - I've only been doing it this week.

As the pressure releases - the water is being drawn in from the header tank which is logical if there is an air pocket which has air which has expanded with heat and forced the water in the system out into the header tank thereby holding its level falsely high.

My suspicion is that it is air coming out, possibly with some steam as I can release the valve with my bare fingers and still keep the skin on them. I suspect steam that was hot enough to be invisible would be a bit less kind.

When I release the valve I keep it open until it sputters water then close it before I get scalded.

The head gasket change and pressure testing were undertaken professionally but not by a Citroen dealeer. I hope they would have detected a cracked head. Also remember, no oil in the water and no water in the engine oil - no guarantee but likely (?)

Today's attempt to deal with it was when I started the engine from cold with the header tank cap off and bleed the blue valve until it ran water, then did the same with the radiator bleed valve untill it ran water. I then put the header tank cap on and did the first leg of my journey. One flaw in the process was I didn't top up the header tank before putting the cap on. This seemed hopeful but when cool the level had dropped - trouble is that was at least partially caused by not topping up the tank at the start.

I repeated the process for the return journey, but topped up the tank before putting the cap on. It looked promising (the tank level), but I wasn't about to bleed the blue valve this time in case I got scalded. I'll see how it looks when cool.

Thanks again for the input and discussion of ideas.

Regards

JP

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Bare hands on the cooling system of a hot engine? Something weird is going on here. I'd assumed you were using a long-handled tool of some sort to keep clear of the hot whatever coming out.

Well it won't show up a porous block, how can it, as for a warped or cracked head - depends on the garage doing the job and what the owner has agreed to pay - "My car is loosing water, fix it" and "How much to change the head gasket on my car, Mate?" are two totally different scenarios...!

Yes.

A porous cylinder head or block is a strange concept though; solid tough metal capable of taking the stress of the combustion cycle, but letting gas pass through to the cooling system? I'm not saying it can't happen, just that its a strange thing to grasp.

In my experience an iffy head gasket leads to 'white smoke' from the exhaust rather than 'air in the radiator'.

Whiskers ( snipped-for-privacy@operamail.com) gurgled happily, sounding much like they were saying :

Citroen have a fine tradition of it - CX Diesel Turbo 2 lump was

Hmm, I bet BMW wished that is was to, just how many engines did they end up replacing for free due to their manufacturing methods / technology creating porous cylinder blocks within the cars normal warranty period?...

Err, one of the by-products of burning petrol is water, so steam from an exhaust is normal (one gets it even on air cooled engines), OTOH if you rally are getting 'white smoke' from the exhaust you should suspect your brake servo....

The service manager in the dealers asked me if there was white smoke on startup. There isn't.

Re. the being able to touch it with bare hands - the valve is a screw on plastic cap, off what I think is the water pump housing which also appears to be plastic (?). As the cap is loosened the presure release of air / steam then water is away from the fingers. Having said that I am vary enough of it when I thought there was a chance of very hot water coming out of it . The cap itself can be handled easily even whenthe metal of the engine is extremely hot.

The whole business is extremely baffling for the sheer volume of coolant it can go through with no apparent indication of where it is going.

My current pet theory - which will be tested tomorrow - is as outlined earlier that there is an air pocket, possibly in the radiator itself or the hose between the radiator and water pump. Having bled the system with the header tank top off and each bleed valve (radiator and water pump) opened in turn, I'll see how it goes. I took it a run tonight and so far it's looking ok.

JP

You could check for popes, as well.

Ian Dalziel ( snipped-for-privacy@lineone.net) gurgled happily, sounding much like they were saying :

But only if it's fitted with a catholic converter.

I've followed the thread with great interest, it is a tricky one, no?

I hate to insult your intelligence but just to check:

You have had a new header tank cap? You do know the header tank is not topped up to the top but only to the level mark which is usually about halfway?

You are certain that there is no external leak of water when the engine is warm?

Assuming all the above to be checked out I reckon you've got a rad leak. The water comes out but evaporates on the hot rad so you don't see it. Then, as it begins to cool it draws air in. You then open the bleed screw and it, er, bleeds. Air.

You could try looking for any crystalline deposits on the rad or joints but there will be areas you can't see properly.

I don't usually reccommend this but after all you've been through I think I'd be inclined to chuck some Radweld in and see if that cures the fault.

Good Luck TonyB

NO! NO! NO!!!!!!!!!!!

PLEASE NO............................

DO NOT USE THAT STUFF, IT WILL BUGGER THE ENTIRE COOLING SYSTEM UP AND MORE THAN LIKELY CAUSE A BLOWN HEAD GASKET - OR EVEN SCRAP THE ENGINE...

I've actually had to replace engines due to damage caused by Radweld, it certainly block up any leaks, the trouble is, it also blocks up water ways.

Cure the problem, don't mask it and store up even more problems.

Yes, New header tank cap fitted - same effect with new or old cap

Re header tank level: yes only to the recommended level.

Certainly no visible signs of a leak.

I think you description of the sequence is right just not sure of the source - could perhaps be the radiator as you say - I also suspect the air that is drawn in is expanding with the heat of the engine and pushing coolant out of the cap which accounts for the volume being lost - if I bleed the system each time I fill it - as I started doing last week - I'm getting an extra 30 mile journey ourt of it before topping up with 1.5 - 2 litres (bizarre!).

The car is back at the dealer and they are trying to identify the problem - nothing showed when the engine was run while the car was on a ramp, so I've said by all means give it a 30 mile run at m'way speeds.

You may well be onto something - proving / confirming it is the problem.

So far the work has been carried out under warranty - therefore I've resisted the Radweld option. Reading Jerry's post I'll maybe give it a miss all together.

I'll post the solution if and when it is found - some other C5 owner may be out there with a coolant loss just waitin' to happen!

JP