Header Tanks / Expansion Tank Plumbing

[agent_zed]

i might be mis-reading your post but just to clarify both the spit/suck and pressurised expansion vessel system are pressurised. The only difference is that the spit/suck reservoir is not pressurised and there will be no air in the system.

 

The pressurised tank will have air in it.

 

Both systems will have a pressurised valve set to a specific poundage they are just in different positions in the system.

 

 

If you aren't running either type of reservoir then the radiator is acting as the pressurised reservoir, which as mentioned will reduce the amount water in your radiator and potentially allow air to be pulled into the engine if the water gets too low as air could be pulled down the narrow tubes and create bubbles. Putting in a reservoir in its simplest form makes sure there is enough water in the radiator to prevent this happening.

[knights_templar]

maybe my answer was a bit crude.

 

But in essence you have it.

 

Basic history of the cooling system

 

thermo cycle, lots of water, tall radiator, many didn't use pumps

 

early pressure system, reduced quantity of water required, can run at a higher temp, some over the boiling point of water, lower radiator height = lower front to vehicle, filler is highest point usually radiator, with safety valve to stop over pressure, filler had level marker, expansion space under pressure cap

 

Pressure system then went non pressure expansion tank, filler does not need expansion space, system is enclosed, expansion spills into bottle, and is sucked back when cool, needs to be completely cold before opening the system or you allow air in and the spit/suck will not work, system will need bleeding.

 

Pressure system with pressurised expansion tank, tank generally needs to be the highest point, but some such as the VW sphere have a pumped feed inlet at the top to bleed the system which allows the filler to be lower, expansion is held with in the system although separate from the main cooling circuit, the cap regulates system pressure and there is often an anti vacuum. generally self bleeding, level can easily be checked visually, but also less emissions from the cooling system.

 

Possibly more advantages and/or disadvantages to each system, but no time to put them down here