#1: Expansion tank constantly pressurized Author: greenpug2222, Location: bradfordPosted: Tue Jan 10, 2012 10:17 am ---- As the title,,,,,
Ive been losing coolant and found its coming from the expansion tank. The tank is not cracked, its coming from under the cap. I renewed the cap and its still doing it.
It does not matter how long i leave the car the system still holds a lot of pressure. I can leave it for a whole day and it still lets off a massive hiss and woush when i take the cap off to check the level.
Any ideas as i can only think of head gasket.
Thanks
#2: Re: Expansion tank constantly pressurized Author: Lee, Location: EnglandPosted: Tue Jan 10, 2012 10:25 am ---- Has it been properly bled?
#3: Re: Expansion tank constantly pressurized Author: greenpug2222, Location: bradfordPosted: Tue Jan 10, 2012 10:44 am ---- erm i guess not but ive only been topping it up and not done a full change.
#4: Re: Expansion tank constantly pressurized Author: Deckchair5, Location: Bath UKPosted: Tue Jan 10, 2012 12:01 pm ---- In a way it's good because if the system is holding pressure for so long then there aren't any leaks in the system
Like Lee says then most likely you have an air pocket trapped somewhere. Cast your memory back and did it ever run very low on coolant?
What happens is the trapped air heats up and expands and that puts the coolant level up and over pressurises so much that coolant pushes past the expansion cap but as the air cools again you find yourself having to top it up and the cycle starts all over again
Read up on how to bleed the system, do it as per the book and that might be the end of your problem (do it now before the cylinder head does go)
#5: Re: Expansion tank constantly pressurized Author: Schumi, Location: Istanbul / TurkeyPosted: Tue Jan 10, 2012 12:47 pm ---- Link for correct bleding ?
#6: Re: Expansion tank constantly pressurized Author: greenpug2222, Location: bradfordPosted: Tue Jan 10, 2012 1:25 pm ---- say what?
#8: Re: Expansion tank constantly pressurized Author: Frost, Location: OxfordPosted: Tue Jan 10, 2012 1:36 pm ---- bleeding is easy find the lowest bleeding point in the cooling system, this could be the thermostat housing, unscrew the nipple untill it comes through with just pure fluid then cap it, then move up the system the next one could be the heater matrix hose. make sure you keep the headder tank topped up the whole time or the process will be pointless, it's best to bleed it when the car is up to temp and with the heaters turned up full that's how i've always done it. if the problem still persists i'd guess head gasket, if you want to be sure about this and you have breakdown cover wait untill its doing it oneday and call the relavant company out and they'll do a check and tell you if it's the head or not
#9: Re: Expansion tank constantly pressurized Author: gixxerkev, Location: wiltshirePosted: Tue Jan 10, 2012 3:01 pm ---- I always thought air bubbles rose to the top so why bother bleeding the system from the thermostat housing (if that were possible) anyway. Go for the heater matrix hose every time as air bubbles rise to the top.
#10: Re: Expansion tank constantly pressurized Author: Frost, Location: OxfordPosted: Tue Jan 10, 2012 3:10 pm ---- i don't question it it's just how we were trained at college so it's what i've always done if the bleed point is there why not use it the landrover only had one bleed point + the headder tank so i see where you are coming from from a logical point of view but my 306 had at least 2 bleed points, maybe 3? and where does logic ever come into french builds?
#11: Re: Expansion tank constantly pressurized Author: Seabook, Posted: Tue Jan 10, 2012 3:42 pm ----
gixxerkev wrote:
I always thought air bubbles rose to the top so why bother bleeding the system from the thermostat housing (if that were possible) anyway. Go for the heater matrix hose every time as air bubbles rise to the top.
there is 3 bleeding point on 206
radiator, thermostat and bulk head
#12: Re: Expansion tank constantly pressurized Author: Bredsticz, Location: M32 8NAPosted: Thu Jan 12, 2012 1:28 pm ---- If its still doing it after bleeding, run the engine with the radiator cap off. Let engine run a minute, rev the engine a bit and look for bubbles emerging. If its a small constant flow it cud well be headgasket on the way out.
This is exactly what my punto was doing and how i noticed it before it had fully gone
#13: Re: Expansion tank constantly pressurized Author: Deckchair5, Location: Bath UKPosted: Fri Jan 13, 2012 11:57 am ---- If the system is still pressurised after a whole day of leaving it then the system is air tight and there are no leaks so it's not likely the head gasket is leaking otherwise the pressure would leak away
Regarding bleeding then air rises to the top of a straight up and down static fluid vessel but when there are horizontal runs and the water is being forced in one direction only then it's easy to develop air pockets at high points in the system. Some coolant systems are easy to bleed and others are a pig, that is why there are many bleed points. It's why every radiator in your house has a bleed valve, air would like to rise to the top and back to the header tank but if it can't get out then it's stuck there
#14: Re: Expansion tank constantly pressurized Author: Bredsticz, Location: M32 8NAPosted: Sat Jan 14, 2012 11:20 am ----
Deckchair5 wrote:
If the system is still pressurised after a whole day of leaving it then the system is air tight and there are no leaks so it's not likely the head gasket is leaking otherwise the pressure would leak away
Regarding bleeding then air rises to the top of a straight up and down static fluid vessel but when there are horizontal runs and the water is being forced in one direction only then it's easy to develop air pockets at high points in the system. Some coolant systems are easy to bleed and others are a pig, that is why there are many bleed points. It's why every radiator in your house has a bleed valve, air would like to rise to the top and back to the header tank but if it can't get out then it's stuck there
Not necessarily going to lose pressure if head gasket has gone. The force from the combustion cylinder to force the combustion into the coolant is a massive amount more than the pressure built up in the coolant tank. The damage in head gasket won't be big enough for it to flow through from coolant to cylinder from just that amount of pressure.
If you understand that
#15: Re: Expansion tank constantly pressurized Author: Deckchair5, Location: Bath UKPosted: Sun Jan 15, 2012 2:20 am ---- If there is a leak, no matter how small, then with say 14psi in the coolant system and zero in the cylinders with the engine off, the system pressure would drop quickly. It's exactly that, the coolant pressure that is monitored when investigating a suspect cylinder head gasket leak It doesn't have to flow, even a pin hole would be enough for it to drop pressure.
The fact it witholds pressure even a day later shows it is an air tight system
If the oil wasn't clean, oil level rising with mayo in the filler cap, bubbles in the header tank or boiling over or white smoke out the exhuast then the next step would be a cylinder leak down test
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find the lowest bleeding point in the cooling system, this could be the thermostat housing, unscrew the nipple untill it comes through with just pure fluid then cap it, then move up the system the next one could be the heater matrix hose. make sure you keep the headder tank topped up the whole time or the process will be pointless, it's best to bleed it when the car is up to temp and with the heaters turned up full 
the landrover only had one bleed point + the headder tank so i see where you are coming from from a logical point of view but my 306 had at least 2 bleed points, maybe 3? and where does logic ever come into french builds?
