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Date:         Fri, 28 Jun 2002 00:03:05 -0700
Reply-To:     Arlen <manx1342@EARTHLINK.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Arlen <manx1342@EARTHLINK.NET>
Subject:      Re: Radiator Design
Comments: To: mark drillock <drillock@EARTHLINK.NET>
Content-Type: text/plain; charset=us-ascii

mark drillock wrote:

> It is a sealed system when not being bled. The energy needed to lift up > to the top is "recovered" by the coolant falling down the other side. It > is called a siphon effect. > > Of course coolant flows through the radiator at idle!

----------------------------------------------------- This is of course true as long as it remains a sealed system, which it is, as long as the bleeder screw is closed and the pressure cap is working properly.

Basic hydraulic theory dictates that pressure felt at any one point in a closed system is felt everywhere in the system. There are many variables of course, which are beyond the scope of this note, but just think about how your hydraulic brake system works. The basics are the same.

If the bleeder screw is open, then there is atmospheric pressure (approximately 14.7 psi) reaching the upper (inner) area of the radiator (pressing down because of gravity, adding to the weight of the coolant) which must be overcome. Hence the need for "revving" to purge the air.

Arlen

ps: Everything I say could be wrong, but not intentionally. ------------------------------------------------------

> That is the primary reason for the radiator fan, cooling down the > radiator when hot coolant is circulating at idle but the van isn't > moving. Then air flow through the radiator must be provided by the fan. > > Mark > > Andrew Fox wrote: > > > > > I believe that is backwards. It should come up the side and down > > > through the cooling veins and then out. This is the direction of the > > > thermodynamics, colder water (relative) will sink.... > > > > This is correct. I will add that the coolant has to raise about 2 > > feet alongside the cooling fins before "waterfalling" into the fins. > > Unfortunately the h20 pump does not generate enough pressure at idle to > > get the coolant "over the top". This is why if you remove your bleeder > > screw at idle nothing will come out. The engine must be running at about > > 2000 rpm to get enough h20 pressure to make the radiator actually cool the > > coolant. Makes me wonder about the effectiveness of this cooling system. > > You would think the VW engineers that designed this cooling system would > > have realized this and built a shorter, fatter radiator or a better > > waterpump. > > > > Andrew > > 86 Westy (has new H20 pump and radiator) > >


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