Is this a coolant hose leak or something else? see pics

[M 80NGD]

If the bleed hose has gone have a check at the one on the other side that goes over the starter motor to the rear heater matrix,I reckon they go up near the engine block where its hottest.I replaced this one very shortly after the bleed hose last year!

Coolant alarm fitted or not it pays to check your hoses regularly

Dabs

I totally agree with Dabs,regular checks of hoses,peventions better than cures

[The Great Pretender]

Air cannot get sucked into the system as it is on the positive side of the pump when the pinhole is at the highest part of the engine, once the coolant level drops below the leak it still curculates. As the system is at atmospheric it will boil at 100c .

Well it happened to me. It was when it cooled down so the positive pressure became a slight vacuum & air was drawn in through a cut in the bleed pipe.

Cutting the damaged section out of the pipe would indeed be a perfectly acceptable repair as long as the rest of the pipe is sound.

Sorry mate...........you may have a problem but you can't have a vacuum when the pipe is open to atmosferic pressure.

[Simon Jones]

Sorry mate...........you may have a problem but you can't have a vacuum when the pipe is open to atmosferic pressure.

...water / air gets hot & expands. When pressure inside the system exceeds atmospheric pressure, the water will leak out of a damaged pipe. Conversely, when water / air cools & condenses, the pressure in the system will drop below atmospheric pressure, so unless the damaged bleed pipe is sat in a container of water, air will be drawn in until the pressure has equalised.

I believe this is the principle behind Thomas Newcomen's atmospheric engine. This can be seen in the following demonstration: http://www.egr.msu.edu/~lira/supp/steam/vacuum.htm

Regardless of what laws of physics may or may not be occuring inside the cooling system, driving the vehicle with a leaky pipe is not how was it designed to be used.

[The Great Pretender]

Air cannot get sucked into the system as it is on the positive side of the pump when the pinhole is at the highest part of the engine, once the coolant level drops below the leak it still curculates. As the system is at atmospheric it will boil at 100c .

Well it happened to me. It was when it cooled down so the positive pressure became a slight vacuum & air was drawn in through a cut in the bleed pipe.

Cutting the damaged section out of the pipe would indeed be a perfectly acceptable repair as long as the rest of the pipe is sound.

How can you have a vacuum when the system is open to atmospheric pressure?

[Simon Jones]

Perhaps we should carry on the physics lesson off-forum , but here's my final comment on the matter:

Is the cooling system normally open to atmospheric pressure? No, it's sealed hence why you get a rush of air escaping when you take the expansion cap off when it's hot.

If we can take it as read for a minute that when warm air condenses in a sealed chamber it will results in a vacuum as demonstrated by the link in my earlier post.

In the case of a hole in the bleed pipe:

When the water gets to boiling point, it expands & pushes water out the hole. When it cools down, there will be less volume of water in the system so there is a larger air gap available. The pressure inside the system will drop below atmospheric pressure so air will be forced into the hole. When the pressures inside & outside equalise, there will be no vacuum left & that point your statement will be correct.

If you drink water from a plastic drinks bottle, the container will contract as the liquid is sucked out. Whem you take it away from your mouth, the air rushes in to fill the space where the liquid was.

[mikeonb4c]

Simon raises an interesting point. I'm trying to understand this (so correct me if I'm wrong), but it seems to me:

If you have air in the system (e.g. the air at the top of the header tank) then unless the hoses etc. expand to an equivalent degree (which I doubt very much!) then the system will pressurise with heat expansion of both the air and, to a lesser extent, the coolant.

If you have a pinprick hole in a pipe, then coolant will be expelled by the pressure (unless air is present at the point of pinprick), decreasing the total volume of coolant+air. The expulsion will only continue until expansion of air+coolant has stopped

When the engine is stopped, the system cools and the air+coolant volume shrinks. Consequently a vacuum is created. As long as the pinhole leak does not have a 'valving' effect (i.e. as long as it allows flow happily in either direction - which is never certain) then air will be drawn into the system.

The cycle will repeat itself (only more exaggerated as air volume in the system is increasing each time) each time the engine repeats the hot / cold cycle).

If the air taken in at the pinprick point is able to get round the system, it should end up in the header tank, displacing coolant and causing a drop in level in the tank which, if noticed, allows a coolant top-up to be done.

If the air is taken in somewhere where it remains trapped, then the effects on the cooling system are unpredictable. You might get cavitation and loss of efficiency in the water pump due to air being present in that area. You may get hot spots in the engine. Who knows.

In the case of a pinprick way down the length of the bleed pipe, the air pulled in may just stay local, being expelled on heating and pulled in again on cooling.

Sorry if I'm completely repeating what's been said, but I'm trying to get my head around it because if I've understood correctly, there is just the remote possibility that pinhole leaks may produce unpredictable and hard to diagnose cooling system malfunction without drop in level in the header tank, although it may be hinted at by an unusual amount of rise and fall due to the pressure of hidden air in the system.

...and all of this before any boiling of coolant, and attendant vapour pressure, is considered

[francophile1947]

although it may be hinted at by an unusual amount of rise and fall due to the pressure of hidden air in the system.

...and all of this before any boiling of coolant, and attendant vapour pressure, is considered

Right Mike. In fact, this method is used by Ben to test that he's bled the system properly - see http://www.igmaynard.co.uk/bongo/forum/ ... 88#p228988

[cheffy34]

Nice one mike explained in a way that i understand

[teenmal]

Why not change the (bleeding hose)and bleed it.

Mal..

[mister munkey]

If the air is taken in somewhere where it remains trapped, then the effects on the cooling system are unpredictable. You might get cavitation and loss of efficiency in the water pump due to air being present in that area. You may get hot spots in the engine. Who knows.

Does this mean I may be in a hot spot of bother?

Pipe fom head to turbo is getting messy rather quickly.



WILL be replaced as soon as I can find one but am I driving into trouble in the meantime?

[daveblueozzie]

OUCH, ive got a headache reading all that. as everyones says change the bleed hose . with any luck problem solved.

[M 80NGD]

If the air is taken in somewhere where it remains trapped, then the effects on the cooling system are unpredictable. You might get cavitation and loss of efficiency in the water pump due to air being present in that area. You may get hot spots in the engine. Who knows.

Does this mean I may be in a hot spot of bother?

Pipe fom head to turbo is getting messy rather quickly.



WILL be replaced as soon as I can find one but am I driving into trouble in the meantime?

Hi MM,I replaced my bleed pipe with reinforced petrol pipe,same diameter,but stronger and easily available from most motor factors. Looking at yours in the picture suggests it's been changed before,noting the after market jubilee clips.

[mick]

If you are really thinking of a temporary fix, don't use gaffer tape ! A much better alternative is 'self-amalgamating' tape, which larger DIY stores stock.

[Dabs]

A much better alternative is 'self-amalgamating' tape, which larger DIY stores stock.

I always carry some of this in the glovebox,just in case!

Dabs

[teenmal]

If you are thinking of a temp repair (CLAMP the BLEED HOSE)