heat builds pressure. wtf? The water pump PUMPS antifreeze threw the motor reguardless of weather it builds pressure, it does create a vaccum to draw the coolant threw the engine

 

Yes the heat expansion of the coolant creates the pressure that the radiator cap regulates. That pressure is used to increase the boiling temp of the coolant.

Don't beleive me answer this;
Why is there no pressure at the cap when the engine is cold no matter how fast you turn the motor?
Why after you turn my motor off does the pressure remain until the motor cools down?
Why do all overflow tanks have to levels a cold low and a hot high?

 

Why is there no pressure at the cap when the engine is cold no matter how fast you turn the motor?
Because you have a neg-pressure at the cap till heat opens the t-stat. Why after you turn my motor off does the pressure remain until the motor cools down? Radiator cap controls presssure and vacume. last answer controls expansion hot to cold. Back to the main question of bleeding the air.After you get the radiator full of coolant get a pressure cap tester and put it on the radiator.This should force the air out when you crack a fitting.If you still cant bleed the air out start looking for a headgasket problem.

 

This is retarded, if you want to continue being retarded I don't care but please don't spread it.

 

I'm with opossum on this one, as the engine heats, the water expands. Without the radiator cap, the water just spills out of the radiator. With the cap, system pressure is regulated to the rated pressure of the cap. Any pressure above that cap rating is bled into the overflow tank. When the engine cools and the system pressure drops, the water that escaped to the overflow tank is drawn back into the cooling system. If you look at the radiator cap, there's a small metal disc right in the middle that gets pushed inward (towards the radiator) by the returning coolant. The cap provides little to no resistance or control of vacuum, only positive pressure in the cooling system.

The water pump does build slight pressure in the block, but since it is a closed system, that pressure is not maintained from pump outlet back to pump inlet. Overall system pressure from thermal expansion of the water is bigger than any block pressure the water pump generates.

agreed!

 

So what you are saying then is you need heat to move water? A water pump puts out pressure hot or cold period. Retarted huh? In the real world of trying to be a mechanic from a key board you both would be out of a job.Funny what happened to to word respect.If you dont show it dont bother posting keyboard repairs.You just dont get it do you.

 

one of the many answers by googling this question:

The water pump is a simple centrifugal pump driven by a belt connected to the crankshaft of the engine.

The pump circulates fluid whenever the engine is running.

The water pump uses centrifugal force to send fluid to the outside while it spins, causing fluid to be drawn from the center continuously. The inlet to the pump is located near the center so that fluid returning from the radiator hits the pump vanes. The pump vanes fling the fluid to the outside of the pump, where it can enter the engine.

The fluid leaving the pump flows first through the engine block and cylinder head, then into the radiator and finally back to the pump.

When the fluid in the cooling system heats up, it expands, causing the pressure to build up.

The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank. This arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled.

 

My friend,
All the water pump is doing is circulating the coolant through the engine and the radiator.
It is a closed loop, the outlet side pushes, as the inlet sucks the same volume at the same time.
Nothing is being added, so that is not the source of pressure.

The thermal expansion of the coolant itself (and any steam that may be produced) is what pressurizes the system.

 

hope this is all cleared up now.

 

Ok, the cooling system pressure, 15-18 psi is caused by expansion of the coolant and is there to raise the boiling point. Early vehicles had an "open" system with no pressure then the pressure caps started.
If you don't believe the water pump will create pressure, you've never seen what it will do to a heater core on a cold day when you turn a 289 7000rpm with the thermostat closed! Watch the hoses, particularly the one from the manifold to the heater when you rev the engine, if the thermostat is closed or mostly closed, it will expand slightly as will the bypass hose. Purging air form a small block Ford is almost as much fun as a 2.2L-2.5L Mopar engine. I usually let it warm up fairly well then once the thermostat opens and stays open I run it around 2000 or so rpm until the heater core etc. are purged. On a van, I usually loosen one of the heater hoses to "burp" the system. On some EFI engines you can use the throttle body heat hoses to do this.

 

Well put EPNCSU2006, quicklook2, and ArdWrknTrk My response wasn't very eligant yours were put much better.

I've never tried to measure the pressure differance across the thermostat but I suspect it wouldn't be any more than 2-3 psi could be interesting though.

It strikes me that the suggestion at the begining of this thread that if the level in the radiator goes down when the engine is revved there's air in the system is probably correct. It's very hard if not impossable to get all of the air out of the cooling system. It seems it would take a lot of heat cycles and movement of the vehicle to get all of the air out of the top corners of the block, the heater core, and upper raidiator hose. I dodn't find it to be a problem and the only real solution is to keep the system closed and drive it.

 

I suppose if you could measure pressure at the pump inlet and outlet there would be a slight difference, but very slight. It would have nothing to do with overall system pressure.

 

no we're saying that the majority of the cooling system pressure is from thermal expansion of the water. There will be a pressure gradient through the system, with the highest pressure being seen in the block with the thermostat closed and the lowest pressure at the water pump inlet. On our race engines we see maybe 5 psi of pressure in the block just due to the water pump. Compare that to the 50-60 psi of system pressure and it's not much.

Summary: the pump is a pump and creates a pressure head depending on resistance it pumps against, however this value is low compared to the overall system pressure regulated by the radiator cap. Heat itself doesn't circulate any water, nor did anyone ever say it did.

 

I did not mean to say the water pump will not create pressure against a "dead head".
What I was trying to say, is that it does not pressurize the coolant system.

I'm sorry if I was unclear....<embarrassment></embarrassment>

 

i do not think revving a cold 289 to 7000 rpm is a real smart thing.