300+ rebuild

[mrsmackpaul]

3 hours ago, Geoff Weeks said:

It has nothing to do with pressure, it has to do with an inverted U bend (at the top of the housing) that is above the inlet and outlet.  It forms a pocket that holds air. You can have gravity or pressure on the coolant and it still will not cause the air to go below the coolant level to pass out of the pump.

I could agree with Geoff, but we would be both wrong then

The first thing people need to understand is what cavitation is

It isn't just air in water 

Anyway I'm sure you'll have quotes and stories that will shoot me down in flames and I'm not getting into a I'm more right than you type of conversation 

We need to understand what cavitation is and what causes it and how a pump actually works and if air really got trapped that easily in coolant system then there would be bleeders all over the block and head and any little defect in the castings

Anyway I'll leave you to think you're right as I'm only a dumb ass skippy the bush kangaroo from Australia ha ha ha

 

Paul

[Geoff Weeks]

11 minutes ago, mrsmackpaul said:

 

 if air really got trapped that easily in coolant system then there would be bleeders all over the block and head 

 

Paul

No need for "bleeders" all over the block, because there aren't cavities that can trap air all over the block. Block has opening on top to the heads, heads have opening on top to the upper water rail, upper water rail has a vent to the degassing tank on top of the radiator. 

 Yes, we could agree but then we both be wrong, as you say. 

 

[mrsmackpaul]

Well I guess engine blocks and heads must be different in the southern hemisphere than in the Northern hemisphere as there are plenty of spots in castings were air can be trapped 

So keeping this polite and well mannered 

If air is simply trapped in the water pump as suggested, why do manufacturers put a little pipe or hose around the pump to the thermostat side ?

 

Paul

[Geoff Weeks]

31 minutes ago, mrsmackpaul said:

 

If air is simply trapped in the water pump as suggested, why do manufacturers put a little pipe or hose around the pump to the thermostat side ?

 

Paul

There are two reasons, for a pipe from the thermostat housing to the pump. One, is a return when the 'stat is closed (bypass), this keeps the coolant circulating. This, however tends to be a larger pipe, and is connected to the inlet side of the pump.

 Often a small hose or pipe from the pressure side is exactly what I am referring to, a bleeder line to to high point in the block to allow the air to escape.

 In Larry' s engine the bypass connects back down at the oil-cooler so not directly connected to the waterpump.

depending on how the waterpump is situated on the block, the bleeder can be internal or external with a line, in each the reason is the same to eliminate a pocket of air.

For the last aprox 50 years, a bottom fill/degassing tank has been used to eliminate air in the cooling system, with vents lines in the upper water rail and in the upper radiator tank. 

On a 3406 the pumps is low and gear driven, there is a large passage from the T stat housing back down to the pump ~1.5" diameter, when coolant from the degassing tank (where the cap and fill are) is directed to the inlet of the waterpump and the air can escape up the bypass line to the T stat housing (and upper water rail vent line) to the degassing tank. Since the bypass line is vertical from the top of the pump, the air pocket is eliminated. Cummins does it different with the waterpump bolted in a casting on the front of the block, with a small hole through to the main coolant passages in the block to allow air to vent out of the pump recess in the block into the main coolant passages in the block and on to the upper water rail. 

[mrsmackpaul]

WOW thats a lot of typing 

Anyway, lets keep it simple because Im a dumb ass

If the air is expelled from the system, why does it have a pipe, going up fown, left, right or were ever to bleed trapped air away ?

As once the air is expelled, there is no air left 

So whats the purpose of this pipe work ?

 

Paul

[Geoff Weeks]

The bypass line is use until the T stat is full open to return the coolant back to the pump to allow it to circulate within the block. The bleed line or passage prevent any air from being trapped in the future. Injector copper sleeves can weep a small amount of air into the coolant on start up. the bleed line or passage makes sure it doesn't get trapped in the top of the pump housing.

Run a de-aeration tank low, and you can get air into the system. By allowing it to escape, you prevent the pump from being air bound.

Take a picture of which lines you are talking about and I will try and tell you the reason for them. 

In all cases, the outlet of the water pump is directed to the bottom of the block, this makes the outlet of the pump lower than the top of the waterpump housing. That makes the housing an air trap. 

There are some (tend to be lighter duty engines) where the outlet of the water pump is to the top of the block or cylinder head, these self vent but direct the coldest water to the hottest part on the engine, which isn't great for even cooling. Most modern engines direct the outlet to the bottom of the block.

[mrsmackpaul]

This doesn't really explain were the air comes from once the air is expelled 

What is this tricky thing called cavitation  ?

What causes it ?

And how can that is alledgedely trapped in a water pump be such a issue ?

How doe's a centrifical pump work ?

 

These are all things that have to be understood to understand how cavitation occurs and what is required to stop it 

Ask a irrigation farmer that relies on centrifical pumps about cavitation and it's effects on pump life and the pipe work connected to the pump

I can tell you as a irrigation farmer, that water will not get stuck in the pump as your suggesting

The moment a centrifical pump is primed and spinning that water is gone 

If it wasn't the the pump wouldn't be primed

So keeping this in mind, assuming that bit of information I have suggested is correct 

Were does this pesky air come from that causes cavitation?

I can assure you it isn't the injector sleeves

And why do some makes of motors never suffer from this and others do all the time ?

I'm trying not to be condescending here, we all learn things differently and I'm trying best to teach people here

Cavitation isn't simple like people think

 

Paul

 

[Joey Mack]

So in my new world.. when we talk about cavitation, we say a gas has gotten into the system. Air is a gas.. this comprimises the movement of fluid through the pumps volute. The action of the water,in this case, mixed with air creates small explosions inside the volute, which pecks away at the volute. When enough of a gap between the impeller and the volute is created, the water will not move properly.  Hence,  and over heating condition.  We all know air seeks the highest point in the cooling system.. venting at that point is key.  Lets take a Mack E-7 for example...  even though there are small tubes at the top of the thermo housing and pump, I have had 100% sucess when I loosen the plug in the front water manilfold behind the thermo housing, as i fill the system back up. When it leaks the air is gone...  

[mrsmackpaul]

When a motor is rebuilt, generally I would remove as much from the cooling system as I can

Leave the radiator cap off until operating temp is achieved and the thermostat opens 

Any air trapped in the motor is released, top the cooling system off, put the radiator cap on, take for a test drive and check everything is okay 

I reckon thats pretty standard across the world and open to correction if I'm wrong and missed a step

Joey your right about cavitation, but what is it, we know the result of it

But what causes it ?

I had it explained to me many years ago in a way that made sense 

Were does this air come from ?

 

Paul 

[Joey Mack]

Paul.  The air enters when there is a failure in the system, or simply when refilling the system after a repair.  If an impellar is worn and cavitation is present the lack of coolant flow causes an overheat condition. Then water is boiled out and through the world of magic, air fills the void..  

Im bluffing on that last part...  I rekon the rad cap can introduce air into the system if it is in poor condition.  When the system cools it creates suction, so I would think any loose fittings will allow air to be sucked in...  Then again... what do I know?  Im just a head scratchin kinda guy...  

[Mark T]

22 minutes ago, Joey Mack said:

So in my new world.. when we talk about cavitation, we say a gas has gotten into the system. Air is a gas.. this comprimises the movement of fluid through the pumps volute. The action of the water,in this case, mixed with air creates small explosions inside the volute, which pecks away at the volute. When enough of a gap between the impeller and the volute is created, the water will not move properly.  Hence,  and over heating condition.  We all know air seeks the highest point in the cooling system.. venting at that point is key.  Lets take a Mack E-7 for example...  even though there are small tubes at the top of the thermo housing and pump, I have had 100% sucess when I loosen the plug in the front water manilfold behind the thermo housing, as i fill the system back up. When it leaks the air is gone...  

Or ????? remove that plug and take your blow gun and blow across it until the coolant comes out after filling it with what goes in at first.   If there's afew gallons in it, it'll suck it up to the thermostat housing. 

[Joey Mack]

Yep that works too.  Either way there will a little spill..

[cruiseliner64]

3 hours ago, Geoff Weeks said:

The bypass line is use until the T stat is full open to return the coolant back to the pump to allow it to circulate within the block. The bleed line or passage prevent any air from being trapped in the future. Injector copper sleeves can weep a small amount of air into the coolant on start up. the bleed line or passage makes sure it doesn't get trapped in the top of the pump housing.

Run a de-aeration tank low, and you can get air into the system. By allowing it to escape, you prevent the pump from being air bound.

Take a picture of which lines you are talking about and I will try and tell you the reason for them. 

In all cases, the outlet of the water pump is directed to the bottom of the block, this makes the outlet of the pump lower than the top of the waterpump housing. That makes the housing an air trap. 

There are some (tend to be lighter duty engines) where the outlet of the water pump is to the top of the block or cylinder head, these self vent but direct the coldest water to the hottest part on the engine, which isn't great for even cooling. Most modern engines direct the outlet to the bottom of the block.

Im finding this very interesting...Heres a picture of the set up on our Cruiseliner.The top water hose(silver) goes from rad tank to stat houseing.Then a hose about 1 inch in size goes from bottom of rad tank to the bottom hose where it comes out of the oil cooler and a small hose from the water rail to top of rad tank.The hose from the water rail is very heavy duty.It has bullhead fittings and is like fuel grade hose.I have wondered what its for......

Paul

Edited 3 hours ago by cruiseliner64

[Mark T]

The MPs had a sucky thing like Bottlehauler had in the picture. Personally, one of the best things I ever aquired was a MightyVac. They work great for suck'n stufff out like coolant when you have something apart. They work good to get stuff back in components too. I was under the impression cavitation was more the result of piss poor cooling system maintainence. Stuff like thinking coolant is fine as long as it's not leaking out or figuring if it works in extreme conditions just leave it alone....or top it off with tap water.  Or using the cheapest coolant even if the manufacturer lists what to use in it (lol) Mixing coolants, like pouring anything in it to shut the light off.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Mark T]

4 minutes ago, cruiseliner64 said:

Im finding this very interesting...Heres a picture of the set up on our Cruiseliner.The top water hose(silver) goes from rad tank to stat houseing.Then a hose about 1 inch from bottom of rad tank to pump and a small hose from the water rail to top of rad tank.The hose from the water rail is very heavy duty.It has bullhead fittings and is like fuel grade hose.I have wondered what its for......

Paul

Pretty standard setup . The tiny one is a vent, the big one is from thermostat to radiator and that one (the blue silicon hose) lets the coolant go from the radiator tank to the engine. That one could be different on different chassis' depending on the recovery tank arrangement.   Bit of a bypass if you will.   The big part of the cooling job is done by the big hoses (upper and lower) as per action of the thermostat. 

[Geoff Weeks]

There are 2 top tanks, the one closest to the tubes is the tank where the big upper hose goes and the coolant passes down the tubes to the bottom tank/hose.

The upper half is the de-aeration tank and is where the cap and where you put coolant in. The 1" line is "bottom fill" line so coolant in the de-aeration can fill the system 

marmon tank.pdf

[cruiseliner64]

Thanks Mark,I do understand the cooling arrangement but the question I have is why is the vent hose of such heavy construction and does it vent air as described by Geoff, since its from the highest point on the engine to the highest point on the rad.I have to say our Cruiseliner was the easiest vehicle I have ever filled with coolant.I filled it to about an inch below the filler neck had coolant at all the bleed points instantly ran it to working temp and didnt even need to top it up!!!

Paul

[Geoff Weeks]

3 minutes ago, cruiseliner64 said:

I have is why is the vent hose of such heavy construction and does it vent air as described by Geoff, since its from the highest point on the engine to the highest point on the rad.

Paul

Braided line is durable and can take pressure well. Most 1/4" hose, like fuel hose would be less durable. Also the reusable hose ends don't loosen with repeated heat cycles like worm drive clamps can.

[Mark T]

37 minutes ago, cruiseliner64 said:

Thanks Mark,I do understand the cooling arrangement but the question I have is why is the vent hose of such heavy construction and does it vent air as described by Geoff, since its from the highest point on the engine to the highest point on the rad.I have to say our Cruiseliner was the easiest vehicle I have ever filled with coolant.I filled it to about an inch below the filler neck had coolant at all the bleed points instantly ran it to working temp and didnt even need to top it up!!!

Paul

Probably if you look at the pressure cap on that system, it's on the higher scale. So it needs a good robust line to do the job.  Some system have a lighter hose for that, but also operate at lower pressures. Gotta have the vent action going on as the coolant expands and contracts during the cycles .

[mrsmackpaul]

So cavitation occours when the liquid, in this case water, seperates into gasses

Oxygen and hydrogen in the case of water

This happens when the delivery side of the pump isn't restricted enough or supply side is to restricted 

Pumps pump less when this happens, like Joey sort of said in different words, centrifical pumps can't pump air

So how to stop this happening in motor, run the right thermostats, don't over rev, maintain a good pump

So why isn't air trapped in the pump housing as Geoff suggests

As soon as the pump starts half of the pump or there abouts is under a lower atmospheric pressure

So what does this mean ? 

What's easier to shift, a bucket of air or a bucket of water ?

A bucket of air of course, so the low air pressure causes the air around the pump to try and escape and the only way out is through the on the delivery side

So why are some motors not subject to cavitation and others susceptible 

Pump design and location on the motor has a lot to do with it

Detroits pump on a 2 stroke is small diameter and down low, this means it makes less pressure or perhaps it makes smaller pressure difference between suction and delivery 

Macks are also better designed 

So the air on cavitation is coming from the liquid been shifted, not staying liquid all the time

There is no air getting into the motor, the liquid in the motor is changing state and once the liquid passes through the pump returns to liquid again

The cavitation is like water hammer on the pipes in house, turns from liquid to gas and back again, over and over again 

The coolant system has a type of water hammer 

No wonder some designs of motors are susceptible to this and it's hard to stop

So trucks got more power and bigger coolant systems, which in turn leads to higher coolant flow, this causes cavitation 

Many a Cat earthmoving machine suffers from this when thernostats are removed

So I'm not having ago at anyone, but it's very clear that some of our standings are not correct on pumps and shifting of liquids and how a centrifical pumps actually work

There isnt a suction side, even though we call it that

There's a low pressure and high pressure side on a centrifical pump

Positive displacement pumps have a suction side, so the supercharger on a 2 stroke Detroit is a positive displacement pump

Anyway enough waffle from me 

I can explain further if needed but won't have a big long drawn argument trying to prove what I'm saying is write

Happy days everyone 

 

Paul

 

 

[Geoff Weeks]

So, how low does the pressure have to be for the coolant to vaporize? As you say there isn't "suction" only pressure below atmospheric. 

If you look how low the pressure has to be for the coolant to turn to vapor, it is well below what a centrifugal pump can produce. 

The pressure cap holds the "suction side above atmospheric, the pressure side can be as high a 46 psi in the block.  

Edited 1 hour ago by Geoff Weeks

[mrsmackpaul]

The coolant doesn't vapourise, it turns into two different gasses and this actually happens in the pump impeller 

 

Paul

[Geoff Weeks]

Liquid changing to gas, has a term, it is the boil point. If you are boiling at the return from the radiator, you are already overheating before any coolant has entered the engine to cool it.

At 50/50 and atmospheric that point is around 223 deg F. And this is on the return side of the radiator.  Where as the de aeration tank is where the pressure cap is and also directly connected to the lower pressure side of the waterpump, that is above atmospheric, often around 10 psi. 

 

[mrsmackpaul]

12 minutes ago, Geoff Weeks said:

Liquid changing to gas, has a term, it is the boil point. 

 

The coolant isn't boiling, it's separating 

Very different 

 

Paul

[Geoff Weeks]

Phase change is phase change! Explain "separating" and why it happens there and not elsewhere.