Evening.

Having ordered my Raceline water rail some 6 and a bit weeks ago, I called to chase it the other day. I was told that they hadn't completed the order because they were waiting on stock of pressure caps from the States, and long overdue despite repeat promises of imminent delivery.

No being the impetuous person I am, I suggested not to worry and send me the rest of the kit anyway, and I'd source my own rad pressure cap from the local motor factors and contacts I've got. But true to form, nothing is that simple. Local motor factors could get me a replacement cap to fit, but the pressure was only 13PSI, which Raceline said was too low. They supply an 18-22PSI cap, and for the love of me, can't find a replacement through any sources at Ford or otherwise to match.

So I turned to the dreaded of all places, eBay....
Stumbled across the two following options, but I'm unsure as to which would be the better choice. So I thought I'd ask for opinions here and see what the general concensus was before I made a decision. Please be brutally honest - I'm sure some have encountered this or similar problems in the past, so those in the know, please speak up!

Options are as follows;

eBay - The UK's Online Marketplace
eBay - The UK's Online Marketplace

Let's hear your thoughts!

Hi, I have the raceline set up and it is a stant cap which looks similar to the second link but it doesn't have the red bit on the right hand side. I am not sure if.that one will fit. I can take a pic of mine if you want?

The 2nd one is the one I have in mine.

Hi where did you get your water rail from, I was considering one for my 2ltr Zetec Blacktop?

I am sure mine ran with a std 13lb cap. Not sure why they suggest a 20lb one is needed, unless expecting to run very high temps (and therefore pressure)

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Originally posted by Greenie
Hi where did you get your water rail from, I was considering one for my 2ltr Zetec Blacktop?

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quote:

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Originally posted by cliftyhanger
I am sure mine ran with a std 13lb cap. Not sure why they suggest a 20lb one is needed, unless expecting to run very high temps (and therefore pressure)

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Wouldn't the standard radiator cap pressure be for a system that has a header tank and thus more volume for the water to expand into so it doesn't reach blow off pressure.
If the Raceline setup has no header tank that'll be why it requires a higher rated pressure cap.

quote:

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Originally posted by MkIndy7
Wouldn't the standard radiator cap pressure be for a system that has a header tank and thus more volume for the water to expand into so it doesn't reach blow off pressure.
If the Raceline setup has no header tank that'll be why it requires a higher rated pressure cap.

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Hi

The reason they specify the use of the higher poundage cap is because the thermostat is so far from the engine it's self that by the time the thermostat See's the temp to open the actual engine temp is far higher. IE poor design and the reason why they are generally frowned upon. Some get them to work others just change to more reliable setups.

Cheers Matt

In a header tank setup you don't fill it to the top so there is quite a large air pocket that can compress so it doesn't go overpressure.
In the raceline setup there might be a tiny amout of air held in the top of the rail if any at all so there is very little for the hot water to expand into I suspect that's why it needs a higher pressure cap.

On a sealed heating system like your Combi at home you have an expansion vessel half filled with air that the water expands into..
When cold the system pressure is 1 bar
When the system is warm the pressure rises to 1.5 bar
The safety valve is set at 3 bar and thus doesn't blow off
When it cools it returns to 1 bar

When the expansion vessel has lost it's pressure or burst there is nowhere for the water to expand to.
When cold the system pressure is still 1 bar
When the system warms up the water has nowhere to expand to
The safety valve now blows off as it maybe reaches 3.5 bar and thus above the 3bar limit

If you'd fitted a 4 bar safety valve because you knew it had limited expansion then the system wouldn't have blown off, this I what I suspect there trying to achieve.

Different application but same principle I'm sure without knowing too many of the technicalities

quote:

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Originally posted by procomp
Hi

The reason they specify the use of the higher poundage cap is because the thermostat is so far from the engine it's self that by the time the thermostat See's the temp to open the actual engine temp is far higher. IE poor design and the reason why they are generally frowned upon. Some get them to work others just change to more reliable setups.

Cheers Matt

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quote:

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Originally posted by MkIndy7
In a header tank setup you don't fill it to the top so there is quite a large air pocket that can compress so it doesn't go overpressure.
In the raceline setup there might be a tiny amout of air held in the top of the rail if any at all so there is very little for the hot water to expand into I suspect that's why it needs a higher pressure cap.

On a sealed heating system like your Combi at home you have an expansion vessel half filled with air that the water expands into..
When cold the system pressure is 1 bar
When the system is warm the pressure rises to 1.5 bar
The safety valve is set at 3 bar and thus doesn't blow off
When it cools it returns to 1 bar

When the expansion vessel has lost it's pressure or burst there is nowhere for the water to expand to.
When cold the system pressure is still 1 bar
When the system warms up the water has nowhere to expand to
The safety valve now blows off as it maybe reaches 3.5 bar and thus above the 3bar limit

If you'd fitted a 4 bar safety valve because you knew it had limited expansion then the system wouldn't have blown off, this I what I suspect there trying to achieve.

Different application but same principle I'm sure without knowing too many of the technicalities

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Originally posted by britishtrident

Modern engines are designed to run hot ISTR The standard Mondeo cooling fan is controlled by the ECU to only switch to full blast at 115c ---- 13psi cap would pop just before that which would trigger boiling. .

[Edited on 23/8/11 by britishtrident]

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Hi

They use an expansion tank system rather than a header tank system to over come that scenario. All in all it's a cock up off a design. Also if you look at where the water goes around the corner in the casting you'll see on some that the orifice is way too small ( little finger tip size ) and on another it is twice that size. !!!

Cheers Matt

If it's such a 'cock up' of a design, how has it successfully been raced in Formula Ford for years?

Also, if this the Zetec or Duratec appliction, the duratec (which I have) retains the thermostat in exactly the same position as the original, it's not in the water rail at all.

[Edited on 23/8/11 by Tiger Super Six]

Hi

As i stated earlier some do get it to work by bodging it. The Zetec one has the thermostat something like 10" away from original fitment. If you do some basic looking / research you will see that there are many many people who ditch the rail and return to a plain old system and cure all the problems the rail induced into there previously perfectly good working system. There is a reason why so many come up for sale SH.

Cheers Matt

Cheers Charlie..........