Expansion tank cap

Expansion tank cap

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mhibbins

Original Poster:

13,820 posts

218 months

Tuesday 24th April 2001
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This cooling system is full of surprises. With a new rad, new water pump and new hoses it's fully operational... apart from it chucks a pint of water on the floor at the end of every journey, doh! I suspect that the cap on the expansion tank must be the wrong one. I'm guessing that it should have two seals; one at the top of the neck and one that pushes down on the sleeve in the neck. In that way if the pressure gets excessive then it can be vented down the overflow tube. Trouble is that my cap only has the outer/upper seal and therefore any excess pressure is vented out of the overflow tube all the time. This means my cooling system is never under any appreciable pressure and at the end of the journey when all the water is supposed to go back into the expansion tank it goes straight out the overflow tube Can anyone either from memory or by having a quick look verify this for me, although don't burn your fingers ? Also, if I'm right, I need a new cap, is the expansion bottle (and therefore the cap) lifted straight off the granada or is it something else entirely? Thanks once again, -- Mark Edited by mhibbins on Tuesday 24th April 09:15

Paul V

4,489 posts

216 months

Tuesday 24th April 2001
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The cap on my S2 has only the rubber seal at the top of the cap, it’s not like a radiator cap, which has a spring-loaded rubber seal. Could you be over filling the system? Mine has the max line about 2” from the bottom of the tank allowing lots of water in when needed without going out of the overflow.

Roy C

4,106 posts

223 months

Tuesday 24th April 2001
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The cap on the expansion tank is not a pressure cap and is only there to enable you to top up the system. Ignore the marks on the (Ford) expansion tank. My S2 has always run with about 1.5" (cold) in the bottom. Any more than that is ejected by the overflow tube when the hot coolant expands. Some cars run with a virtually dry expansion tank (TVR Mark).

mhibbins

Original Poster:

13,820 posts

218 months

Tuesday 24th April 2001
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In that case, how high should it be filled in the tall metal tube with the rad cap? It seems to settle at about 4 inches from the top once it has ejected the water it doesn't want, I'd assumed it should be full. -- Mark

Roy C

4,106 posts

223 months

Tuesday 24th April 2001
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In that case, how high should it be filled in the tall metal tube with the rad cap? It seems to settle at about 4 inches from the top once it has ejected the water it doesn't want, I'd assumed it should be full. -- Mark
It should be full.
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mhibbins

Original Poster:

13,820 posts

218 months

Tuesday 24th April 2001
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It should be full.
If it's full when cold then it chucks water out of the overflow pipe attached to the neck of the expansion tank when hot. If it's full when it's hot then it doesn't but when cold it settles back down to a level of 3/4 inches below full in the metal cylinder. I guess my expansion tank could be broken which would explain things... I'll check that tonight. Any other ideas? -- Mark Edited by mhibbins on Tuesday 24th April 12:02

TVR Mark

45 posts

222 months

Tuesday 24th April 2001
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If you recently drained (part drained) the system they do suffer from air locks. Some times I can drain it and top it up no probs, other times it air locks.

LeeBee

773 posts

223 months

Tuesday 24th April 2001
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OK this is what I have been told......You have the metal swirl tank which is where the system has to be filled up from.You also have your expansion tank (Rover part), the normal rad cap goes on the swirl tank and the non pressure cap goes on the expansion tank (don't get them mixed up!).Now in an ideal world the expansion tank should have a few inches of coolant in it and the swirl tank should be full, but it doesn't really work like this in practice! they tend to find their own levels, so as long as the car doesn't over heat it should be ok.My S2 will spit out coolant if the swirl tank is filled to the top (tried it 10 times, did the same accepted it finds it's own level! and had this confirmed by a TVR technician) and there are no air leaks Cheers Lee

mhibbins

Original Poster:

13,820 posts

218 months

Tuesday 24th April 2001
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Thanks Lee. When I got home and checked it more carefully the top of the swirl tank and the expansion bottle are not far off at the same level so I can't see how the swirl tank can ever be full unless the relative level varies between cars. The level it has found in the swirl tank is higher than the top of radiator so the rad must be full which is the important thing. I've repeated the fill/eject cycle about 10 times and I'm happy I've got all the air out so I'll carry some water with me and see how it goes. -- Mark

mhibbins

Original Poster:

13,820 posts

218 months

Wednesday 25th April 2001
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Sorry, another question (it won't happily find it's level )... There are a number of hoses coming from the swirl tank. In the diagram in Steve Heath's book on page 149 (second edition) it shows the expansion tank connected to the swirl tank to the top connector, ie the one in the neck of the swirl tank. My car has the expansion tank connected to the 2nd one down, ie the one just below the neck of the swirl tank. If they were the other way around I can see that my swirl tank could be full and not blowing out of the expansion tank. Which is the correct way around? Thanks, -- Mark

LeeBee

773 posts

223 months

Wednesday 25th April 2001
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Yep just had a look and that is correct so the first thing you want to do is reconnect your system as the diagram.If you need any help with the pipes etc let me know and I will take a pic of mine (pipes that is! )and email it to you? Cheers Lee

thegamekeeper

2,282 posts

221 months

Wednesday 25th April 2001
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Hate to contradict LeeBee but the pressure cap should be on the expansion bottle and the plain (non pressure cap goes on the swirl pot.) This allows water to expand into the expansion bottle as the cooling system gets hot. The pressure then builds up in the system allowing the water to boil at a higher temperature. When the water reaches the pressure of the pressure cap it then vents to atmosphere preventing the hoses from bursting. In theory if the cooling system is working correctly the max presure of the cap will never be reached and the cooling system will run at equilibrium and water will be exchanged between the swirl pot and the expansion tank dependent on the operating temperature

mhibbins

Original Poster:

13,820 posts

218 months

Wednesday 25th April 2001
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Yep just had a look and that is correct so the first thing you want to do is reconnect your system as the diagram.If you need any help with the pipes etc let me know and I will take a pic of mine (pipes that is! )and email it to you?
Ah ha! That'll be the problem then. I'll change them in the morning. Even though it's probably my fault I'll still be found doing the happy dance -- Mark Edited by mhibbins on Wednesday 25th April 23:27

mhibbins

Original Poster:

13,820 posts

218 months

Wednesday 25th April 2001
quotequote all
quote:
Hate to contradict LeeBee but the pressure cap should be on the expansion bottle and the plain (non pressure cap goes on the swirl pot.) This allows water to expand into the expansion bottle as the cooling system gets hot. The pressure then builds up in the system allowing the water to boil at a higher temperature. When the water reaches the pressure of the pressure cap it then vents to atmosphere preventing the hoses from bursting. In theory if the cooling system is working correctly the max presure of the cap will never be reached and the cooling system will run at equilibrium and water will be exchanged between the swirl pot and the expansion tank dependent on the operating temperature
That's what I would have thought as if the pressure cap is on the swirl pot and the pressure does cause flow into the overflow tank then the action of the pressure cap on the swirl tank (with the hoses connected correctly) will never allow the water in the expansion tank back into the system... so what's the point of the expansion tank? The Steve Heath book does agree with Lee however. -- Mark

Roy C

4,106 posts

223 months

Thursday 26th April 2001
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The Steve Heath book does agree with Lee however.
And so do I. TVR built them with the pressure cap on the swirl tank. All the cars I have seen are like this (apart from one that had serious cooling problems because it had been bodged).

mhibbins

Original Poster:

13,820 posts

218 months

Thursday 26th April 2001
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Quick update: changed over the hoses, topped it up and parked on the M4 and waited... and it all works a treat. Thanks -- Mark

LeeBee

773 posts

223 months

Friday 27th April 2001
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Good news!, as for cap positions everyone I have ever spoken to agrees with me and I have had enough of these cars (10+)in my workshop which are the same.Also it does say this in the owners manual! Cheers LeeBee

LeeBee

773 posts

223 months

Saturday 28th April 2001
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One other point on the caps though is that although both TVR and other related people say it has to go as per the manual the M series is the opposite I believe? Time to investigate! LeeBee

GreenV8S

26,840 posts

223 months

Monday 30th April 2001
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Hate to contradict LeeBee but the pressure cap should be on the expansion bottle and the plain (non pressure cap goes on the swirl pot.) This allows water to expand into the expansion bottle as the cooling system gets hot. The pressure then builds up in the system allowing the water to boil at a higher temperature. When the water reaches the pressure of the pressure cap it then vents to atmosphere preventing the hoses from bursting. In theory if the cooling system is working correctly the max presure of the cap will never be reached and the cooling system will run at equilibrium and water will be exchanged between the swirl pot and the expansion tank dependent on the operating temperature
As standard, the swirl tank has a pressure cap and the overflow catch tank has a plain cap. And this is the only scheme that makes sense to me. There may be cars out there that work the other way round, but it doesn't make sense to me. On most production cars you will see a clear plastic tank that acts as a separator and expansion tank. In order to act as an expansion tank it has to have hot water flowing through it. In order to act as a separator, it usually has an offset inlet to induce swirl, a high inlet velocity so any bubbles are carried in, and a low outlet velocity so they aren't carried out again. As the system gasses up the pressure rises past the cap's rated pressure and the cap starts to weep, and the gas steadily escapes. On the S series, Griffiths etc, TVR use a metal swirl pot to perform this function. The small inlet is at the top, offset to induce swirl. The large outlet is at the bottom. It has a pressure cap on. There is also an overflow tank. The confusion comes because the tank TVR use for the overflow tank is actually a standard expansion tank. But it is not used as an expansion tank, it is just an overflow catch tank. It is not pressurised and has a plain cap on. If you fit the caps the wrong way round you prevent the system from pressurising properly. The expansion tank generates pressure partly from gas generated within the cooling system but (in modern engines which are relatively well sealed) mainly because of expansion of the air as it is heated by the water. Since the overflow tank isn't heated, it doesn't build up pressure. This means you will get nucleate boiling in the engine and reduced cooling efficiency. The nucleate boiling will displace water into the overflow tank and may build up some pressure, and if you have a leaky engine it will eventually build up full pressure as the gas is blown into the overflow tank. But that isn't the way it is supposed to work, and stresses the engine unecessarily. The key thing to check for to see whether your cooling system works like this, is whether the tank has water circulating through it. If it doesn't, it is not an expansion tank and should probably not be pressurised. Hope this makes sense, Peter Humphries (and a green V8S) Edited by GreenV8S on Monday 30th April 19:14