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matttav

Original Poster:

178 posts

153 months

[news] 
Monday 21st January 2002 quote quote all
I must be blind.. but I can't find the specification for the swirl tank and expansion tank caps.

Are they both 15 lb??? I didn't think so.. but both mine are 15lb

Cheers Matt

markbigears

1,534 posts

155 months

[news] 
Monday 21st January 2002 quote quote all
i looked at mine the other day......both are 15lb, and both have springs, look the same to me..... not sure if this is correct, can someone enlighten me, us........ta mark

johno

7,614 posts

168 months

[news] 
Monday 21st January 2002 quote quote all
The swirl tank cap is a 15lb cap. You do not need a pressure cap on the expansion tank though, just a standard cap which will not have a pressure rating.

Cheers

Mark

vodkakid

1,076 posts

158 months

[news] 
Monday 21st January 2002 quote quote all
i think these are the wrong way round if you think about it the pressure cap should be on the expantion tank other wise what the point of the expantion tank if you have a pressure cap half way round the system

andy c

matttav

Original Poster:

178 posts

153 months

[news] 
Monday 21st January 2002 quote quote all
Urmm.... The wierd thing is I thought the bible states that the pressure cap should be on the swirl tank and a lesser pressured cap on the expansion tank. But most people may have them the wrong way around.... my mucho confused!!

Cheers Matt

PS I did find the right 15 lb cap as Halfords for 3.50...I think the Halfords part number is 601.. I saw they also did a 13lb cap the right size as well
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richb

30,593 posts

170 months

[news] 
Monday 21st January 2002 quote quote all
quote:
i think these are the wrong way round if you think about it the pressure cap should be on the expantion tank other wise what the point of the expantion tank if you have a pressure cap half way round the system - andy c


No - the sprung cap goes on the swirl tank. The white plastic tank is not an expansion tank, it is really an overflow reservoir and has the non sprung cap on it. Take my word for it, my S3c had the wrong way round (predictably) and when I swapped them back it cured some of my water loss problems. R...

GreenV8s

23,471 posts

170 months

[news] 
Monday 21st January 2002 quote quote all
quote:

i looked at mine the other day......both are 15lb, and both have springs, look the same to me..... not sure if this is correct, can someone enlighten me, us........ta mark



Assuming your pipes are plumbed in the same as mine ...

Swirl tank is pressurised with a 15 lb cap. Overflow tank is unpressurised, it is not in the circulation system (only one inlet/outlet) and is just an overflow catch tank. One reason this can lead to confusion is conventional cars typically have a combined swirl pot/header tank with a small bore inlet and a large bore outlet, which water circulates through. TVR used the same/similar part but only plumbed in as a catch tank, no water circulates through it. You should always fit a pressure cap to the swirl tank so the air volume is heated by the water and builds up pressure quickly. Put them the wrong way round and it will kind of work but relies on gas generation to pressurise the system.

If you put 15lb caps on both tanks I reckon your system will run at 30 psi which is fine as long as your hoses will take it!

Cheers,
Peter Humphries (and a green V8S)

Peter Humphries (and a green V8S)

vodkakid

1,076 posts

158 months

[news] 
Monday 21st January 2002 quote quote all
but i only lose water if i have them your way round richb

andy c

richb

30,593 posts

170 months

[news] 
Monday 21st January 2002 quote quote all
quote:
but i only lose water if i have them your way round richb - andy c



Ah well I'm only saying what worked for me an dseems to be the correct way according to TVR and others...

vodkakid

1,076 posts

158 months

[news] 
Monday 21st January 2002 quote quote all
i think that most things differ from car to car so who knows but then again i dont know much

andy c

johno

7,614 posts

168 months

[news] 
Monday 21st January 2002 quote quote all
The pressure cap definitely fits onto the swirl tank. The top hose on the swirl tanbk feeds any pressure released overflow to the expansion tank on the bulk head. The expansion tank on mine then has an overflow pipe out of it to drain at a certain level. Therefor this is no necessity to have a further pressure cap as this is not where the pressure is released.

If yours is the same and you do have a pressure cap on the expansion and an overflow pipe like mine then having a 15lb pressure cap on this aswell will not mean your system is at 30lb. But double check you have the overflow pipe. Mine leads off to behind the brake servo and inner wheel arch in front of the pedal box.

Cheers

Mark

John Bull

74 posts

156 months

[news] 
Monday 21st January 2002 quote quote all
I agree totally with Mark, 15lb cap on the swirl-tank and any cap on the expansion/overflow tank. The bible backs this up too.

John
Black S3

matttav

Original Poster:

178 posts

153 months

[news] 
Tuesday 22nd January 2002 quote quote all
OK,

So from what everyone says...it might be worth having a 15lb cap on the swirl tank... and putting any fitting cap on the expansion tank, perhaps drilling a hole through it to make it non pressurised????

would that make sense??

Cheers Matt

Roy C

3,531 posts

170 months

[news] 
Tuesday 22nd January 2002 quote quote all
quote:

OK,

So from what everyone says...it might be worth having a 15lb cap on the swirl tank... and putting any fitting cap on the expansion tank, perhaps drilling a hole through it to make it non pressurised????

would that make sense??

Cheers Matt


There is a hole in the expansion bottle already - the overflow pipe.

Roy

GreenV8s

23,471 posts

170 months

[news] 
Tuesday 22nd January 2002 quote quote all


There is a hole in the expansion bottle already - the overflow pipe.

Roy



Which is *above* the pressure seal, if I remember right?

johno

7,614 posts

168 months

[news] 
Tuesday 22nd January 2002 quote quote all
quote:



There is a hole in the expansion bottle already - the overflow pipe.

Roy



Which is *above* the pressure seal, if I remember right?



not on the expansion bottle. It is on the Swirl tank !

johno

7,614 posts

168 months

[news] 
Tuesday 22nd January 2002 quote quote all
Mattav,

Email me. I have just had a look at some pictures I have from when I was doing another job on the engine. They show the overflow pipe from the expansion tank and the pressure overflow pipe from the swirl tank.

Cheers

Mark

matttav

Original Poster:

178 posts

153 months

[news] 
Tuesday 22nd January 2002 quote quote all
Cheers Mark..... Email on its way!!

djburns

80 posts

156 months

[news] 
Sunday 27th January 2002 quote quote all
Apologies for dragging all this up again, but after looking at my S1.5, I can see the logic in having the sprung cap on the swirl tank with an ordinary cap on the overflow/expansion as long as the coolant can drain back into the system when it cools. Steve Heath mentions a sprung cap with a one way valve to allow this. Surely this an unusual part?My expansion tank has the overflow pipe at the cap and therefore should have an ordinary cap to allow overflow without pressure.BTW when I checked my car, the sprung cap was on the expansion tank and plain cap on the swirl tank, this was after coming back from Peninsular having had a coolant change!
confused? I am now!

cheers John

PeterC

386 posts

155 months

[news] 
Monday 28th January 2002 quote quote all
I run my S3 with the pressure cap on the expansion tank + plain cap on the swirl tank. This works fine and does not cause any problems with coolant loss or overheating.

I have compared this set up with other S3's and they all have been the same. Interesting that your car returmed after servicing was also set up this way.

If you look at the pipework in the car and the various connections, this must be the way it was intended.

Putting the pressure cap on the swirl tank, just serves to isolate the all pipework between it and the expansion tank. I think someone long long ago, in a time now forgotten (Star Wars fan) did this and it cured their "probelms" disappeared. When his problems were probably leaks and splits in the isolated pipes.
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