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Making a cooling system self bleeding?
RazMan - 30/10/06 at 07:49 PM

I have a possible cooling problem which reared its head while on the rollers last week. I have an electric water pump (with its own controller) and no thermostat so my options are a bit limited but how do I make sure that any air is automatically bled out of the system?

I have a header tank connected to the inlet side of the water pump which feeds the engine block. The engine outlet is about the highest part of the system so is it good to run a small bleed hose from there back to the header tank? Do I need a restrictor to prevent too much water being pumped through?

Simon - 30/10/06 at 08:43 PM

Raz,

My understanding od the point of a header is that it's self bleeding. The top pipe into the header is were air enters (from highest point in cooling system), and another feed to system from H/tank is where it returns. The header allows for pressure build ups, but thereoretically keeps the cooling system topped up.

HTH

ATB

Simon

JoelP - 30/10/06 at 08:55 PM

a good header tank (surely all as simon says?) would have two pipes, a bigger one to dump water to the bottom of the systema and a small one to let air out the top. You could use a few small ones if you worked out you had several high points. As far as my knowledge goes, if it only has one pipe to the bottom its more like an expansion tank (though probably techanically not)

907 - 30/10/06 at 08:57 PM

Hi Raz


I would have the expansion pipe from the highest point and scrub the lower one.

As the engine heats up water expands into the h/tank, together with any air bubbles,
and when it cools down water will be sucked back into the system.
The pipe needs to enter the h/tank at the bottom and be about half full when cold.

This is what I have on my Lotus and it seems to work.

HTH

Paul G

RazMan - 30/10/06 at 10:36 PM

quote:
Originally posted by Joel

a good header tank (surely all as simon says?) would have two pipes, a bigger one to dump water to the bottom of the systema and a small one to let air out the top. You could use a few small ones if you worked out you had several high points. As far as my knowledge goes, if it only has one pipe to the bottom its more like an expansion tank (though probably techanically not)


That's pretty much how mine is now, but I have a small pipe outlet (which is capped at the moment) at the top of the header tank. I was thinking if this was connected to the engine outlet, any air could bubble out into the tank. When I initially filled the system, there was loads of air trapped which eventually dispersed with a few tickover warm-ups with the pressure cap off and the heater full on.
This is my tank (rh one)



Come to think about it I am not even sure I should have a pressure cap on the tank - waddya reckon?

[Edited on 30-10-06 by RazMan]

[Edited on 30-10-06 by RazMan]

Chippy - 30/10/06 at 11:01 PM

Pressure caps are fitted to increase the boiling point of the water, not sure by what amount, but if you take it out water will boil at 100 degs, and pretty soon no water left. HTH Ray.

RazMan - 30/10/06 at 11:15 PM

Yep I understand the effect of having the pressure cap but I am unsure if my system needs to have one. I am hoping that my header tank can act as an expansion reservoir too (to save having another tank) so it is only half full to allow for expansion.
I guess if the system boils over under extreme conditions, a pressure cap will allow it to run a little hotter without losing water. My system seems to run at about 80 - 90 degrees but I havent taken it on the road yet - just a rolling road which probably isn't very representative of 'normal' conditions.

907 - 30/10/06 at 11:26 PM

I hope the pic below explains better.

I replaced the pressure cap on the rad with a solid one.
The rad overflow is connected to the expansion pipe from the t/stat to the tank.
I added a bleed screw to the tee for when the system is first filled.

I keep meaning to remake the copper one in stainless.
(Which is why I offered to make you one. Do the two together.)

Exp/tank cap blows at 10 psi.

Paul G

[Edited on 30/10/06 by 907] Rescued attachment e-tank-pipe-s.jpg
Rescued attachment e-tank-pipe-s.jpg

RazMan - 31/10/06 at 08:15 AM

In my case (middy setup) the rad is 2 metres away from the engine so I intend to bleed off the engine outlet which goes to the top hose.

procomp - 31/10/06 at 08:45 AM

Hi to utilise the system properly use the return from the header tank (the larger lower pipe) back to the pump. And the smaller pipe from the header tank at the top to the highest point of the cooling system and if possible also to the top of the rad.
Some of the vauxhaul header tanks have two air bleed pipes one for the engine and one for the rad wich is the prefferd way of doing it . Tanks for the vauxhaul vectra can be brought brand new for less than £10 but get a preshure cap from after market for £3 as the gm one is a litlle pricey. Also as said replace the original on on the engine or rad with a blank replacement.
That is the basic layout for the modern setup as just using the header as a expansion tank will cause all sorts of grief on some engines but is the way most of the jap cars are plumbed.

cheers matt

02GF74 - 31/10/06 at 08:48 AM

quote:
Originally posted by RazMan
Yep I understand the effect of having the pressure cap but I am unsure if my system needs to have one.


hmmm, I wonder if there is more to it thqn that ... put iut this way, I have never come across a car without a pressure cap hence would say it is a bad thing not to have one.

Even if you are not at boiling point, the water will have expanded plus the air in the expansion bottle will have expanded too so it is running at a higher pressure - whcih may be beneficial (don't know enough chemistr.ohgysics of water or water/anti-freeze mix to say why).

BKLOCO - 31/10/06 at 08:55 AM

Mike, remember the probs I had with my system "pumping over"?
This was caused by the so called air bleed from the top of the thermostat housing.
When I removed that and went to a setup the same as Pauls (907) I had no further problems.
I have now replaced that "air bleed" hose but have T'd it out of the top hose on the rad and that seems to work fine as well.
I think it is a case of differential pressures in the system. As the thermostat opens and closes in certain circumstances it allows air to be "pulled" back into the system through the very hose that is supposed to "bleed" the air out.

RazMan - 31/10/06 at 09:24 AM

Ah - maybe a one-way valve might be the answer to prevent air getting sucked back in the system.

I will do as suggested and tap into the top hose (at the engine end) as this is the highest point on the system, running a small bore hose back to the top of the header tank - maybe with a one-way valve.

Thanks for all the help guys

procomp - 31/10/06 at 11:28 AM

Hi dont complicate things to start whith do what you said and see then try a one way valve after. All of this plumbing wiil only really show up problems once on the road and running.

cheers matt

Chippy - 31/10/06 at 11:07 PM

Further to my comment on Rad pressure caps. You state your engine runs at 80 to 90 degs, well so do most, (not all), others, and the amount that the cap lowers the temp can best be seen in the fact that if you remove the cap, the whole lot will boil out, (this should not be tried at home) as they say! Regards Ray