Radiator blanking cap leaking

[Emilyandrose]

Hi all,

 

I hope someone on here can help. I have had a coolent leak, which I fixed. Fingers crossed 🤞.  But I am trying to put the blanking cap back on after filling the system back with coolent, and it just keeps leaking. The seal on the original was completely gone and it looks as though the previous owner had used silicone to reseal it. So I have bought a new one, and I am having the same issue.  

 

Any suggestions?

 

What sealant would I use if went down the sealant route, the same sealant as the would use on the stove?

[Alan de Enfield]

8 minutes ago, Emilyandrose said:

I hope someone on here can help. I have had a coolent leak, which I fixed. Fingers crossed 🤞.  But I am trying to put the blanking cap back on after filling the system back with coolent, and it just keeps leaking.

 

Does your new cap have the 'spring' underneath ?

 

The reason that the small hose is coming of the side is so that as the water expands, the spring lifts and allows the water to flow up the hose inti the expansion chamber (you do have an expansion chamber ?)

If you have got a 'blanking cap', then as the water expands it cannot get to flow up the pipe and it must go somewhere so it squirts out under the cap. Nothing you do will stop it.

[Emilyandrose]

No the cap is flat. No spring

41 minutes ago, Alan de Enfield said:

 

Does your new cap have the 'spring' underneath ?

 

 

The reason that the small hose is coming of the side is so that as the water expands, the spring lifts and allows the water to flow up the hose inti the expansion chamber (you do have an expansion chamber ?)

If you have got a 'blanking cap', then as the water expands it cannot get to flow up the pipe and it must go somewhere so it squirts out under the cap. Nothing you do will stop it.

I have just retried with one with a spring,  but the pipe inlet blocks it. 

[Tony Brooks]

That pipe is a bodge repair, the pipe is too far into the neck.

 

It looks to me as if the filler neck has split on the turn-over at the top at about 2 o'clock on the photo, so it will never seal. So you either need to get the little pipe resoldered in its correct position, then a normal pressure cap will seal on the bottom of the neck, or you need a new filler neck.

 

 

[Iain_S]

1 hour ago, Tony Brooks said:

That pipe is a bodge repair, the pipe is too far into the neck.

 

It looks to me as if the filler neck has split on the turn-over at the top at about 2 o'clock on the photo, so it will never seal. So you either need to get the little pipe resoldered in its correct position, then a normal pressure cap will seal on the bottom of the neck, or you need a new filler neck.

 

 

Agree. But if the OP has a separate header tank, there still needs to be a seal on the top of the filler neck. The metal to metal of a standard pressure cap won't cut it.

[Tony Brooks]

23 minutes ago, Iain_S said:

Agree. But if the OP has a separate header tank, there still needs to be a seal on the top of the filler neck. The metal to metal of a standard pressure cap won't cut it.

 

True, but depending upon skin tank volume, the manifold tank might be enough as long as the level is kept low. That would solve the overflowing problem, but not utilise the expansion tank. I am not sure how the filler neck is fitted, if it bolts or screws on that would be an ideal change, but if glued in place the change could be difficult. The OP could get a pressure cap with rubber under the cap to seal the neck, but as soon as the coolant expanded past the lower seal, it would still leak through that crack.

If the manifold is taken off, inverted and one could get the underside of that top flange clean enough, I think there will be a groove that could be filled with solder to seal the leak. I don't think it would last if done from the top, and it would need better soldering than that shown on the pipe joint into the neck. Maybe even a lowish melting point silver solder.

[Alan de Enfield]

2 hours ago, Emilyandrose said:

I have just retried with one with a spring,  but the pipe inlet blocks it. 

 

Unfortunatley you have a broken boat.

If you are capable then it needs a fix as per Tony's suggestions , alternatively, you need to get it to an engine repairer and hopefully they will do a better job than the last cowboy !

 

 

[ditchcrawler]

11 minutes ago, Alan de Enfield said:

 

Unfortunatley you have a broken boat.

If you are capable then it needs a fix as per Tony's suggestions , alternatively, you need to get it to an engine repairer and hopefully they will do a better job than the last cowboy !

 

 

better than that well known company  Bodgeit and Scarper

[Alan de Enfield]

Just now, ditchcrawler said:

better than that well known company  Bodgeit and Scarper

 

I believe they did the initial repair ..........................

[Tony Brooks]

Another thought/way.

 

Some Vetus engines, I assume it is Vetus by the gold paint, have a hexagon plug in the top of the thermostat housing. If (and it is a big if) the OP's is like this, then the hose on the filler neck could be removed and reattached to an adaptor in the plug thread.   Then the application of a blow torch should melt the solder to allow the pipe stub to be removed from the neck, then a high pressure spring type cap would seal on the bottom of the filler neck while keeping the header tank in use. The pressure would not be important as long as it is higher than the one on the expansion tank.

[Emilyandrose]

You are right, there is a split on the top. It splits into the neck and then runs left. I did not see that. 

 

Now it make sense  that the cap with the new rubber gasket would not seal. 

 

Thanks for the help. 

 

[cuthound]

3 hours ago, Alan de Enfield said:

 

Unfortunatley you have a broken boat.

If you are capable then it needs a fix as per Tony's suggestions , alternatively, you need to get it to an engine repairer and hopefully they will do a better job than the last cowboy !

 

 

 

3 hours ago, ditchcrawler said:

better than that well known company  Bodgeit and Scarper

 

You can always take legal action over sub-standard work.

 

One company of solicitors specialising in this type of work is Doowee, Cheetham and Howe...

[Ronaldo47]

Reminds me of an apparently genuine incident reported on the news a few years ago at the time that "Minder" was being shown on UK TV. A group of British tourists in the USA were travelling in a bus that was involved in an accident, some of them suffering injuries. An ambulance-chasing lawyer was surprised that none of them took up his offer of help. His name was Arthur Dayley.

[Slim]

Don't have any direct knowledge of the manifold tank concerned but could it be the seal between the filler neck and the manifold tank itself? I had this on a Polar manifold tank some years ago. In the end I had to replace filler neck complete with a new gasket. It wasn't a straightforward job.   

[David Mack]

14 minutes ago, Ronaldo47 said:

An ambulance-chasing lawyer was surprised that none of them took up his offer of help. His name was Arthur Dayley.

A bit like the British spy posted to Poland in 1964. Despite knowing nothing about him the Polish authorities were suspicious from the start. His name? James Bond!

 

[Bod]

7 hours ago, Emilyandrose said:

No the cap is flat. No spring

I have just retried with one with a spring,  but the pipe inlet blocks it. 

It might be possible to replace the entire neck, speak to a vehicle radiator repair company first, they will require the manifold to be removed and taken to them.

The brass neck will fixed to the cast manifold, soldered?

 

Bod

[Tony Brooks]

I think that you can get filler necks already fixed to a steel base with two holes in the base so it can be screwed to the manifold after removing/cutting off the old filler neck. This would require drilling and tapping the manifold, but it will probably be the easiest and most durable repair. I think we had a link not long ago.

 

ASAP Supplies also supply filler necks that screw into the manifold, but I don't know if the OP's is screwed into the manifold.

Edited March 20, 2025 by Tony Brooks

[David Schweizer]

Things may have changed recently, but radiator caps always came with different pressure relief ratings and different spring lengths. Although the basic cause of the leak seems to be a faulty overflow outlet jonit, I am still persuaded to ask if the OP is trying to fit the correct cap.

[Tony Brooks]

9 hours ago, David Schweizer said:

Things may have changed recently, but radiator caps always came with different pressure relief ratings and different spring lengths. Although the basic cause of the leak seems to be a faulty overflow outlet jonit, I am still persuaded to ask if the OP is trying to fit the correct cap.

 

They also come in long and short neck, but neither the pressure nor the neck length will have any effect with the plain flat sealed cap. Even if the cap's pressure was nominally too low on a canal boat cooling system filled to the correct level, it should not allow it to leak, because the coolant level will not rise enough. The pressure is to prevent localised boiling inside the engine under high power and load conditions, that you don't get on canal boats very often.

[David Schweizer]

2 hours ago, Tony Brooks said:

 

They also come in long and short neck, but neither the pressure nor the neck length will have any effect with the plain flat sealed cap. Even if the cap's pressure was nominally too low on a canal boat cooling system filled to the correct level, it should not allow it to leak, because the coolant level will not rise enough. The pressure is to prevent localised boiling inside the engine under high power and load conditions, that you don't get on canal boats very often.

 

Yers, that is what I meant by "...different spring lengths." One of the header tanks on Helvetia's central heating system used a short neck cap, and a long neck cap could not be fitted without a great deal of force.

[Tony Brooks]

59 minutes ago, David Schweizer said:

 

Yers, that is what I meant by "...different spring lengths." One of the header tanks on Helvetia's central heating system used a short neck cap, and a long neck cap could not be fitted without a great deal of force.

 

Looking at the crack in the top flange, the way it seems to have propagated from the point that the cap would have exerted maximum upwards force. It would not surprise me in the least if that is what happened and a long neck cap was forced on. Luckily it seems there may be a pressure cap on a remote header tank so a plain sealed cap should solve the leak, once the crack is addressed,

[David Schweizer]

3 hours ago, Tony Brooks said:

 

Looking at the crack in the top flange, the way it seems to have propagated from the point that the cap would have exerted maximum upwards force. It would not surprise me in the least if that is what happened and a long neck cap was forced on. Luckily it seems there may be a pressure cap on a remote header tank so a plain sealed cap should solve the leak, once the crack is addressed,

 

I may have missed it, but I cannot see where the OP might have suggested that there is also a remote header tank, or if there is, where it is located. Helvetia had two tanks, one being a standard Bowman expansion tank on top of the engine, and another at the far end of the boat where the last coolant fed radiatoor was located. If I had fitted a blanking cap to the remote header tank, the heating simply would not work because of restricted  circulation, and if I had fitted a blankng cap to the Bowman, I suspect that the heating system tank would have served as the engine pressure relief and probably spewed water out all over the front cabin floor. Or am I missing something?

 

 

Edited March 21, 2025 by David Schweizer

[Tony Brooks]

It is an educated guess because the overflow pipe seems to run uphill in the very first photo. If it were just an overflow, I would expect it to run down hill so expanding coolant did not overtop the filler neck. The OP has not said much to clarify the situation so it remains and Ian D seems to think there maybe a separate header tank.

[Slim]

18 hours ago, Tony Brooks said:

I think that you can get filler necks already fixed to a steel base with two holes in the base so it can be screwed to the manifold after removing/cutting off the old filler neck. This would require drilling and tapping the manifold, but it will probably be the easiest and most durable repair. I think we had a link not long ago.

 

ASAP Supplies also supply filler necks that screw into the manifold, but I don't know if the OP's is screwed into the manifold.

That's exactly what I did. Unfortunately the old neck was larger and some of the original hole had to be filled with weld to allow drilling and tapping for fixing bolts.  As I said it wasn't straightforward,.😊 

Edited March 21, 2025 by Slim

[Momac]

On 20/03/2025 at 14:16, Tony Brooks said:

 

 

It looks to me as if the filler neck has split on the turn-over at the top at about 2 o'clock on the photo, so it will never seal. 

It certainly is cracked and the crack seems to be not just at the 2 o clock position but propagating around the top of the filler neck. I agree there is no surprise this is leaking. Looks like its been leaking some time as evidenced bu the missing paint. Sooner or later it will fail altogether.