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.