am I right
- Thread starter NickNorth
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Pikey
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did yu post that twice? - or was it my pc?
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Don't think water pumps spin fast enough to produce cavitation at idle speeds in a cold engine nor does the water flow fast enough through the system to create any notable venturi affect. Take boat trailer hub. Well know to fill with water when dipped into the sea after a road trip to the launch site. This is caused by the axle bearings heating warming the grease and the air inside the hub, as the air expands it is expelled. When the hub is dipped into the colder water the air contracts and draws water in past the seal which just like the water pump seal is designed to prevent grease escaping and not to prevent ingress. The OP says the bubbles occur hot or cold. I cannot see that air is being drawn into the system with engine hot and system pressurised through the water pump seal. Not possible. Slightly possible with worn seal and partial vacuum caused by cooling. Otherwise a none starter.
Pikey
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1st time it missed the first half of the equatoration off so had to edit it. but it posted a new thread instead
. so did a quick delete.
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Cavitation can occur wth the prop completly under water, it is caused by pressure differences along the prop blade causing deep low pressure bubbles that implode and can actually knock bits off the blade in doing so.
not completely right
Cavitation - Wikipedia, the free encyclopedia
If my learned friend would like to explain how two bmw 2.5 td lumps as fitted to omega can.
When cold no leaks from water pump, run up and air bubbles and no leak.
Only when persistent high speed motorway work did it drip.
Oh and should you doubt my diagnosis as water pump-it went from 134000 new pump to 215,000 and then failed an mot
I'm more than willing for a science lesson on the physics I have seen with my own eyes
Pikey
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errm I'll think you find it does especially if the thermostat is open or removed.
It's also the reason for filling ya system with a good quality antifreeze. As this inhibits the oxygen content of the engines coolant.
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One of the time frames we are talking about is drawing air in when the engine is cold. There is little or no water circulation and therefore little or no flow at all at this time. When the engine is warm there would have to be a serious suction to draw air into the pressurised system from ambient air. How did we manage in the past without all these super additives? You just stuck anti freeze, mostly Glycol, in before winter and drained it out in summer. Motors were maintained flushed out at least twice a year. The fit and forget stuff we use now is the main reason most Rover V8s blow up.
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Maybe so, but good enough for a short explination. Thought i already explained that. Just look at what you said above and compare it to what i said about negative pressure, positive pressure and vac formed by cooling.
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I think your digging a hole, how far are you going?
At least i'm digging in the right direction. You have no idea where your going. We will have to agree to disagree i suppose.
Okay so give me a physics lesson on the bmw lumps I talked about. (not what you think, but a reasoned mathematical solution)
also explain why I must be wrong when centrifugal force throws liquid out to boundary.
this page should get you started
http://www.mathsrevision.net/alevel/pages.php?page=84
also explain why I must be wrong when centrifugal force throws liquid out to boundary.
this page should get you started
http://www.mathsrevision.net/alevel/pages.php?page=84
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Your starting to get stroppy now. No need to, just read up on vacuum and negative, positive pressure. I am sure it will dawn on you at some stage. As your engine heats up it creates a positive pressure within the cooling system this is designed to increase the temperature at which the coolant boils. If your pressure cap is not as new as it should be, it can vent pressure before the 15 psi that it should release it at. This is a oneway vent, air is not drawn back into the system as the engine cools. This creates a partial vacuum in the cooling system, sometimes you will hear it release as you remove the cap, this is not always a pressure release but air being drawn in. Are you following this? As air is a little thinner than water it will go in when water cannot leak out. So as in the senario presented by the OP and also the one presented by yourself with the engine cold there is no leak of air in nor leak of water out. Quite possible. Now picture a situation were you have a vacuum within the cooling system caused by cooling as the air within the system shrinks. If the seal was badly enough worn air could be drawn into the cooling system by the vacuum whilst the engine is stopped. Because there is a negative pressure in the system and a positive one outside it. When the engine starts and the worn shaft begins to turn and wobble about it is highly likely air could be drawn in by the vacuum because until the engine warms a little there is still a negative pressure within the system and a positive one outside it. Once the engine warms and the negative pressure within the system goes positive the only thing that can happen if the seal is worn badly enough is that water will be forced out. That perfectly describes your beemers symptoms. Now go and have cool beer and calm down.
Your starting to get stroppy now. No need to, just read up on vacuum and negative, positive pressure. I am sure it will dawn on you at some stage. As your engine heats up it creates a positive pressure within the cooling system this is designed to increase the temperature at which the coolant boils. If your pressure cap is not as new as it should be, it can vent pressure before the 15 psi that it should release it at. This is a oneway vent, air is not drawn back into the system as the engine cools. This creates a partial vacuum in the cooling system, sometimes you will hear it release as you remove the cap, this is not always a pressure release but air being drawn in. Are you following this? As air is a little thinner than water it will go in when water cannot leak out. So as in the senario presented by the OP and also the one presented by yourself with the engine cold there is no leak of air in nor leak of water out. Quite possible. Now picture a situation were you have a vacuum within the cooling system caused by cooling as the air within the system shrinks. If the seal was badly enough worn air could be drawn into the cooling system by the vacuum whilst the engine is stopped. Because there is a negative pressure in the system and a positive one outside it. When the engine starts and the worn shaft begins to turn and wobble about it is highly likely air could be drawn in by the vacuum because until the engine warms a little there is still a negative pressure within the system and a positive one outside it. Once the engine warms and the negative pressure within the system goes positive the only thing that can happen if the seal is worn badly enough is that water will be forced out. That perfectly describes your beemers symptoms. Now go and have cool beer and calm down.
Stroppy? not in the least and if you had read the symptoms there was zero leakage unless motorway run.
Therefore your hypothesis is floored as the system went beyond any possible negative pressure from cold and when normal operating temperature still dragged air in.
Only when stopped after motorway run did it leak.
Further to this as centrifugal forces throw outwards how can you be so sure there is any coolant behind back of impeller and pump body if the clearance is small enough?
Causing a venturi effect
http://leisure.prior-it.co.uk/diy-build-pond-venturi.shtml
Please feel free to discuss
GRATCH
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Stroppy? not in the least and if you had read the symptoms there was zero leakage unless motorway run.
Therefore your hypothesis is floored as the system went beyond any possible negative pressure from cold and when normal operating temperature still dragged air in.
Only when stopped after motorway run did it leak.
Further to this as centrifugal forces throw outwards how can you be so sure there is any coolant behind back of impeller and pump body if the clearance is small enough?
Causing a venturi effect
Ummmm...... I was with you up to stroppy, then you lost me. Any chance we can have an english translation?
Ummmm...... I was with you up to stroppy, then you lost me. Any chance we can have an english translation?
air drawn in behind back of impeller from shaft seals as the liquid is flung way from impeller shaft.
Water being bigger molecules than air= no water leak.
my view unless someone can show me a definitive.
pond venturi example
Note on the situation we discuss bearing run out and seal flexibility would affect behaviour.
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GRATCH
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Awww bugger, I've gotta go read the thread now.....hang on two... er ten minutes.
kds
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If the pump has any play in it just change the bloody thing and come back and tell us its fixed please !
GRATCH
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Ok, all read, wammers science I personally think is flawed , and I would agree with fanatics reasoning in the real world.
If the water pump has a faulty seal on the shaft, the action of trying to pump liquid round hot or cold would mean that air, with less viscosity, would be more likely to be sucked in through said faulty seal than coolant would be forced out through the faulty seal.
If the water pump has a faulty seal on the shaft, the action of trying to pump liquid round hot or cold would mean that air, with less viscosity, would be more likely to be sucked in through said faulty seal than coolant would be forced out through the faulty seal.
