Which way should the flow through be, in at top or bottom ?

Logic says in at top as cold water sinks but as it's a pumped system does it matter ?

Nige

not sure,
but iwould have thought in at bottom, air out of the top

I think most systems do hot water into top and cold out of the bottom,

Steve


[Edited on 7/1/07 by stevec]

The aerial atom rad has 2 bottom entries so that the water flows up one half of the rad and down the other. Not only that, it is a long way from the rear engine.
Whatever way you plumb it, run a small bleed pipe from the top of the rad or top hose to an expansion bottle.
The larger pipe on the expansion bottle should go on the opposite hose or bottom of the rad. This will ensure that there are no airlocks.

Hi Nige

Many pre-war cars had no water pump and relied on "Thermo-Syphon". This explained in: http://www.austin7club.org/Peter%20Booth.htm
Thermo syphon would not support a heater but it was surprising how much heat came through into the pasenger area from the engine compartment. Nevertheless, early motorists were a hardy breed particularly when you consider the harshness of Winters 50 or 60 years ago.
Water pumps pushed in the same direction as thermo-syphon but allowed the luxury of a heater. I remember that Ford produced an "Export" water pump that was a bolt-on accessory driven by the outside of the fan belt. This also allowed a heater to be fitted. It's amazing how basic cars were and yet people undertook some incredible trips and endurance events in them. Makes us look soft!
alb
John

I asked this question some some back. Logically you would have thought that a bottom feed would be better for expelling air but most cars feed from the top - probably a legacy of the thermal syphoning many years ago.
Actually when you think about it, you feed hot water in at the top and as it cools it naturally sinks, a kind of eco pump

Pinto pumps in at the bottom as i think do most.
Hot water flows from bottom to top as does the latent heat, if you didi it from top to bottom you would get a serious hot spot at the top as the dissapated heat would tend to rise heating the already hot water entering at the top.
Your central heating radiators fill from the bottom to maximse the radiation effect.
IMHO.

Water pumps generally suck cooled water from the bottom of the rad, if it was sucking from the top, the slightest lowering of coolant level would cause the whole system to fail

quote:

---

Originally posted by RazMan
probably a legacy of the thermal syphoning many years ago.
Actually when you think about it, you feed hot water in at the top and as it cools it naturally sinks, a kind of eco pump

---

I thought most pumped pass the cylinder head then straight in to the top.

The reason being that if the head is hot enough to cause the water to boil (which is quite lightly at full load) then the bubbles will quickly move into the header tank or expansion bottle.

If you try and fit a rear rad in a front engined car you get all sorts of problems if you do not allow for the steam with a small bore bypass hose.

I have never owned a car that fed hot water into the lower hose.

Regards Mark