Slow coolant leak
Discussion
Morning all,
I seem to have a slow coolant leak in my S3. It runs perfectly for approx. 500 miles then decides to overheat due to lack of coolant (usually after 'spirited' driving). A mechanic friend took a look and said that my swirl pot opening/pressure cap may be leaking under pressure due to bubbling paint at the opening (see picture - paint was stripped back to inspect for rust).
An inspection of the expansion tank cap (non-pressure) also showed that the seal is not intact - is this a critical seal?
I know that Quiton Hazell stock non-pressure caps, but does anyone know if I can buy pressure caps from anywhere?
What is the general concesus on stainless swirl pots too?
Cheers,
Alex
I seem to have a slow coolant leak in my S3. It runs perfectly for approx. 500 miles then decides to overheat due to lack of coolant (usually after 'spirited' driving). A mechanic friend took a look and said that my swirl pot opening/pressure cap may be leaking under pressure due to bubbling paint at the opening (see picture - paint was stripped back to inspect for rust).
An inspection of the expansion tank cap (non-pressure) also showed that the seal is not intact - is this a critical seal?
I know that Quiton Hazell stock non-pressure caps, but does anyone know if I can buy pressure caps from anywhere?
What is the general concesus on stainless swirl pots too?
Cheers,
Alex
I had exactly the same problem on mine. I replaced the non-pressure cap on the swirl pot and it was all sorted.
There is some debate as to where the non-pressure cap should be placed - swirl pot or header/expansion tank. I've never tried it on the header tank and my car has never overheated or had any issues with cooling other than eventually needing new hoses.
Non-pressire caps are readily available. For example...
http://tvr-parts.com/tvr-parts/part-details/tvr-k0...
Stainless is nearly always very lovely but expensive. However, I took my swirl pot off when I was changing the hoses, stripped the plastic coating off it and polished it up with a set of mops to a near mirror finish I have to occaisionally spray it with silicon (making sure I don't spray the belt!) to keep any rust at bay and when people see it, they think it's stainless!
There is some debate as to where the non-pressure cap should be placed - swirl pot or header/expansion tank. I've never tried it on the header tank and my car has never overheated or had any issues with cooling other than eventually needing new hoses.
Non-pressire caps are readily available. For example...
http://tvr-parts.com/tvr-parts/part-details/tvr-k0...
Stainless is nearly always very lovely but expensive. However, I took my swirl pot off when I was changing the hoses, stripped the plastic coating off it and polished it up with a set of mops to a near mirror finish I have to occaisionally spray it with silicon (making sure I don't spray the belt!) to keep any rust at bay and when people see it, they think it's stainless!
Edited by NaCl on Monday 11th April 09:18
My 2 penneth:
Swirl pot should have pressure cap with syphon-back capability to expel coolant to the header tank when heating up and to suck it back when cooling.
For this to work you need the right cap with an under cap seal (to meet the top of the neck) as well as a seal at the bottom where it meets the bottom of the recess in the neck. Its always worth looking at the condition and tightness of these.
The header cap is there for stopping muck getting in only and the header should vent to atmosphere (this may cause a debate)
The pipe between the header and swirl pot must be well sealed also.
Stainless swirl pots are great if they come with a quality brass or stainless neck. Most brass necks are shocking. Get one made of stainless. Stainless ones can have a leak at the 'to the header tank' connection of not welded up properly as the heat of welding can make this joint go bad.
I found a cap on eBay
Swirl pot should have pressure cap with syphon-back capability to expel coolant to the header tank when heating up and to suck it back when cooling.
For this to work you need the right cap with an under cap seal (to meet the top of the neck) as well as a seal at the bottom where it meets the bottom of the recess in the neck. Its always worth looking at the condition and tightness of these.
The header cap is there for stopping muck getting in only and the header should vent to atmosphere (this may cause a debate)
The pipe between the header and swirl pot must be well sealed also.
Stainless swirl pots are great if they come with a quality brass or stainless neck. Most brass necks are shocking. Get one made of stainless. Stainless ones can have a leak at the 'to the header tank' connection of not welded up properly as the heat of welding can make this joint go bad.
I found a cap on eBay
Top Gear TVR said:
My 2 penneth:
Swirl pot should have pressure cap with syphon-back capability to expel coolant to the header tank when heating up and to suck it back when cooling.
For this to work you need the right cap with an under cap seal (to meet the top of the neck) as well as a seal at the bottom where it meets the bottom of the recess in the neck. Its always worth looking at the condition and tightness of these.
The header cap is there for stopping muck getting in only and the header should vent to atmosphere (this may cause a debate)
The pipe between the header and swirl pot must be well sealed also.
Stainless swirl pots are great if they come with a quality brass or stainless neck. Most brass necks are shocking. Get one made of stainless. Stainless ones can have a leak at the 'to the header tank' connection of not welded up properly as the heat of welding can make this joint go bad.
This ^^^^^ Swirl pot should have pressure cap with syphon-back capability to expel coolant to the header tank when heating up and to suck it back when cooling.
For this to work you need the right cap with an under cap seal (to meet the top of the neck) as well as a seal at the bottom where it meets the bottom of the recess in the neck. Its always worth looking at the condition and tightness of these.
The header cap is there for stopping muck getting in only and the header should vent to atmosphere (this may cause a debate)
The pipe between the header and swirl pot must be well sealed also.
Stainless swirl pots are great if they come with a quality brass or stainless neck. Most brass necks are shocking. Get one made of stainless. Stainless ones can have a leak at the 'to the header tank' connection of not welded up properly as the heat of welding can make this joint go bad.
There was a bulletin published by TVR that said the same.
Having the pressure cap on the plastic expansion tank means the plastic expansion tank is under pressure along with the hose that conveys the coolant to it and any coolant getting past the pressure cap is lost.
I've thought about this long and hard in the past and it has hurt my brain. I can see the sense in what everyone has said, but the way mine is plumbed and capped seems to work well. If I give the car a thrashing, stop, look at the header tank, there is coolant in it. Then, when it all gets cold, it is empty again and the level in the swirl is back to where it should be, having sucked it back. So, although my system perhaps might not be technically right, it functions and never overheats or requires the coolant topping up. Naturally, I'm reluctant to change anything ("If it isn't broken..."etc.)
One thing I really can't get my head round is a pressure cap on the swirl tank with a springloaded seal in the base of the neck that somehow lets coolant back in to the swirl pot chamber from the header tank as the system cools. Surely the spring keeps the seal tight and no amount of pressure will get past it 'the wrong way' - unless I'm missing something obvious (maybe this could be a "I'll get me coat" moment).
One thing I really can't get my head round is a pressure cap on the swirl tank with a springloaded seal in the base of the neck that somehow lets coolant back in to the swirl pot chamber from the header tank as the system cools. Surely the spring keeps the seal tight and no amount of pressure will get past it 'the wrong way' - unless I'm missing something obvious (maybe this could be a "I'll get me coat" moment).
Edited by NaCl on Monday 11th April 10:46
Edited by NaCl on Monday 11th April 10:49
NaCl said:
I've thought about this long and hard in the past and it has hurt my brain. I can see the sense in what everyone has said, but the way mine is plumbed and capped seems to work well. If I give the car a thrashing, stop, look at the header tank, there is coolant in it. Then, when it all gets cold, it is empty again and the level in the swirl is back to where it should be, having sucked it back. So, although my system perhaps might not be technically right, it functions and never overheats or requires the coolant topping up. Naturally, I'm reluctant to change anything ("If it isn't broken..."etc.)
One thing I really can't get my head round is a pressure cap on the swirl tank with a springloaded seal in the base of the neck that somehow lets coolant back in to the swirl pot chamber from the header tank as the system cools.Surely the spring keeps the seal tight and no amount of pressure will get past it 'the wrong way' - unless I'm missing something obvious (maybe this could be a "I'll get me coat" moment).
The little brass disk on the underside of the spring loaded seal is a one way valve that opens to allow the water back into the swirl pot. The valve is opened as the the water contracts, creates a vacuum and pulls on the disk. If your cap does not have the disk in place then it wont allow the water back into the swirlpot, plus you have the wrong cap. One thing I really can't get my head round is a pressure cap on the swirl tank with a springloaded seal in the base of the neck that somehow lets coolant back in to the swirl pot chamber from the header tank as the system cools.Surely the spring keeps the seal tight and no amount of pressure will get past it 'the wrong way' - unless I'm missing something obvious (maybe this could be a "I'll get me coat" moment).
Edited by NaCl on Monday 11th April 10:46
Edited by NaCl on Monday 11th April 10:49
But if your setup is not causing issues then leave it as is.
Time to get your coat
Edited by Oldred_V8S on Monday 11th April 11:03
awep said:
Thanks guys - I'll go ahead and replace the two caps and see how things go.
Stainless swirl pot might have to wait a while! What paint is best to use to touch up the existing one?
whilst your coolant'less i would contact 'shauns3c' on here & get a stainless swirl pot knocked up, also nows the perfect time to change over to silicon hoses if its something you want to do.Stainless swirl pot might have to wait a while! What paint is best to use to touch up the existing one?
awep said:
A tester pot of red dulux it is then!
Maybe better going for Hammerite Smooth or better still put your money towards a stainless one 
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