GT6 Boiled Over...

[Kevin Atkins]

1 hour ago, Gully said:

Worth checking that your rad cap isn't too deep for the neck of the radiator. If the sprung seal is completely compressed, it can't lift to release the pressure. Mind you, it's unlikely - main issue I had was finding a cap deep enough!

Gully

Thanks Gully - just had a look, neck flange to lower seat was just over 20mm, the cap measured around the same.. in fact, thinking about it, my addition of an extra top seal might compromise the lower pressure seal so I might remove the extra seal I added, but it doesn't look like an issue with the lower sprung seal, spring seems to have plenty of travel left.

2 hours ago, johny said:

Yes mine has blocked on more than one occasion but I have an after market aluminium radiator which has a tiny overflow pipe. Cant say Ive ever had infated hoses though😮

I've had a closer look at the overflow pipe - the radiator neck pipe is fine, all clear; the pipe itself was also completely clear of obstruction but was a fairly thin wall plastic pipe and there was a bit of a kink just ahead of where it attached to the radiator, and it was quite long so the bottom of the pipe was dredging the bottom of the expansion bottle. I'm wondering whether it was either collapsing at the kink, or possibly too long, or maybe the pipe to radiator seal wasn't perfect with it being plastic, so air being drawn in during cooling? I have replaced it with some 1/4" petrol hose, good tight fit at the radiator neck, and cut so that it reaches maybe 3/4 of the way into the expansion bottle, not bottoming. Will see how that goes..

[johny]

2 hours ago, Kevin Atkins said:

 I have replaced it with some 1/4" petrol hose, good tight fit at the radiator neck, and cut so that it reaches maybe 3/4 of the way into the expansion bottle, not bottoming. Will see how that goes..

Yes the overflow pipe has to be strong enough to resist a slight vacuum as it sucks coolant back into the rad however clear pipe is best as you can then verify that it is always full of coolant and air is not getting in somewhere...

[DanMi]

the overflow pipe would not collapse at the slight kink and cause the system to be over pressurised as the high pressure would open the kink (unless mechanically held), It may prevent coolant being sucked back in but that is not the problem. Heralds work fine without the expansion bottle, they just expel a little water if full, then when cool down it looks a bit empty but it expands again to fill when hot, so it should work ok even without the overflow bottle/pipe

Edited July 13, 2023 by DanMi

[Ian Foster]

Hi Kevin

Slightly disappointing news, but at least you know that all is well on the head gasket front.

I would certainly suggest running with the heater on hot for quite a long time after a refill, to make sure there is proper circulation and allow any trapped air to work its way out. I suspect you do still have air in the system. You mentioned you had elevated the front and managed to get some more air out. Was that with the engine running.

In your original post you said you had fitted a new radiator. It might be worth measuring from the top of the neck to the shelf of the lower seal, just to make sure that it hasn't been built wrongly. It does sound as though you might have  rather flimsy hoses and this might be more of an issue on the Mk3 with the 13lb/sqin cap compared to the Mk1/2 with a 7lb/sqin cap.  A standard top hose from Canleys or the TSSC shop should be fine though, without the expense of going to silicon.

The overflow pipe should be fine as the clear plastic, just make sure you have a half decent fit and/or hose clamp onto the radiator neck. If it is kinked near the top cut that bit off. 3/4 depth into the overflow bottle should be fine. My cold level in the bottle is at 1/2 depth, rising by approx 50mm when fully hot. 

Keep at it and good luck. I'm sorry that I am not closer to Cheshire!

Ian

[Pete Lewis]

quick thought on your air locks   does the thermostat have a jiggle pin in its rim to let air escape whenits closed

if not drill a 3mm hole in the rim 

Pete

[Kevin Atkins]

5 hours ago, Ian Foster said:

You mentioned you had elevated the front and managed to get some more air out. Was that with the engine running.

Hi Ian,

Thanks for the pointers - yes I ran the engine with the front jacked up and massaged hoses. I've done some measurements of the rad and cap and all looks OK from a mechanical point of view, so I think the rad is alright.

I've attached a shot of the hose after a run, with the engine fully warmed up, and I don't like the look of it, it's clearly bulging. There doesn't seem to be any reinforcement - nothing woven into it, it's just a moulded rubber hose with welded seams. I think I'll look at replacing it - your point re. Mk 3 and higher system pressure is interesting.

I also checked engine and radiator temperature with an infrared thermometer just after the run - the stat housing was around 84 - 86 C, the radiator bang on 82 C, so I think the cooling system is working fine.

5 hours ago, Pete Lewis said:

quick thought on your air locks   does the thermostat have a jiggle pin in its rim to let air escape whenits closed

if not drill a 3mm hole in the rim 

Pete

Thanks Pete - the new thermostat didn't have a jiggle pin in it, so I did drill a 3mm hole in it, having seen a recommendation you made in another thread I think.

[johny]

Have you confirmed the reservoir bottle level goes up by approximately 50mm from cold to hot Kevin? If so then the system isnt being subjected to anything more than the 13psi of the cap and the hose must be weak...

[Kevin Atkins]

2 hours ago, johny said:

Have you confirmed the reservoir bottle level goes up by approximately 50mm from cold to hot Kevin? If so then the system isnt being subjected to anything more than the 13psi of the cap and the hose must be weak...

Bingo.. I think you might be on to something here Johny - just taken the car for a short blast. Engine was tepid to begin with - not stone cold but cool, and the top hose was back to its 'non-ballooned' state. I marked the bottle before I set off.

On my return, engine fully warm, opened the bonnet, hose bulging again.. and no change in level in the reservoir bottle. I'm sure I checked the metal take-off tube in the radiator neck but will check again when the engine is cool. If it's clear, wondering if another possibility is that the cap plunger is obstructing the take-off tube, but will rule out the tube first.

As is probably clear by now, due to lack of understanding of how the cooling system actually works (although I've got a much better idea now, thanks to all), my fault diagnosis skills aren't great 😜

Will post back with an update....

[Kevin Atkins]

The engine has cooled sufficiently, so I've just been out to check the overflow pipe on the radiator neck. It is completely clear of any obstruction. I did note that the black paint inside the filler neck felt very 'tacky', so wondering whether maybe the paint is interfering with the cap plunger lifting properly? I have now cleaned all the paint off the inner seal seating surface, back to bare brass.. will see what happens.

[Ian Foster]

1 hour ago, Kevin Atkins said:

On my return, engine fully warm, opened the bonnet, hose bulging again.. and no change in level in the reservoir bottle.

On that basis the radiator cap or overflow pipe is not allowing excess coolant to be expelled into the expansion bottle.

If the pipe is clear, then it must be the radiator cap. At design pressure the lower section of the radiator cap is supposed to lift off the lower sealing surface in the radiator neck and coolant flows via the space between the upper and lower seals into the overflow pipe to the expansion bottle.

Have you tried different caps?

Ian

[johny]

Wait a minute though, if theres air in the system this compresses as the engine warms up so the radiator cap doesnt have to lift to relieve the pressure generated by the expansion of the coolant.

This is how some Triumph models avoid having a reservoir bottle because you leave a gap at the top of the radiator which absorbs the expansion instead of pushing coolant out. However in the GT6 there isnt space in the rad to do this so it must be full and have a bottle.... 

[Ian Foster]

12 hours ago, Ian Foster said:

and no change in level in the reservoir bottle.

This is the concerning bit, which leads me to still suspect the cap.

Photo attached of my top hose, which definitely has a fabric reinforcement (probably supplied by Canleys).

Kevin, I have a used but serviceable 13lb radiator cap going spare if you would like it.

Ian

[Iain T]

I'm following this thread with interest as my expansion bottle doesn't seem to fill with any water when the engine is hot. I have a Bastuck rad and new cap. Anyone ever measure the depth from the top of the neck to the bottom seal surface? 

Iain 

[Kevin Atkins]

4 hours ago, Ian Foster said:

Kevin, I have a used but serviceable 13lb radiator cap going spare if you would like it.

Thanks Ian, that might be one of the next steps, much appreciated. I have ordered a reinforced top hose from a seller on eBay - apparently UK made and from the photo looks similar to yours, much sturdier than what I've got fitted at the moment - I'll try that first and see. I've got two rad caps, both are giving the same results.

I'm beginning to wonder if instead of the cap lifting at 13 psi, the hose is just swelling - ie, the hose 'springiness' is enough to keep the cap seal from lifting? The other possibility that I can see is that the cap plunger is obstructing the neck take-off tube sufficiently that it's preventing correct venting - I'm half minded to experiment by slightly flattening the circumference of the plunger adjacent to the orifice..

1 hour ago, Iain T said:

I have a Bastuck rad and new cap.

That sounds like a similar setup to mine then - I'm assuming mine is also a Bastuck item, bought new from Rimmers about six months ago, seems nicely made. I'll post back when I've fitted the new hose - it might be a few days until I receive it.

On a different, more positive note.. I've just put the car through its first MoT since 2007, following extensive work in the last six months, and she went through with no advisories! That's made it all feel worthwhile, so these niggles will just be a process of elimination.. the old girl will come right in time 🙂

[Iain T]

Somefink wrong 'ere! 

The depth on my rad neck is more than from seal to seal on the cap! Therefore the bottom seal stands no chance of pressurising the system?

Iain 

 

[johny]

The centre vacuum release valve of the cap does seem to be standing pretty far away the lower rubber seal... I take it when you install the cap theres no need to push down to compress the spring before locking it because theres no contact between seal and neck anyway!

[Ian Foster]

Iain

That does sound odd!

I have just popped the rad cap off to check mine.

Radiator neck 19.05mm, cap (7lb) 20.2mm. My spare 13lb cap is 19.4mm. There are witness marks on both seals on the cap indicating they are making contact with the neck.

For info, water was being held in the overflow pipe and released down into the overflow bottle as soon as I opened the cap. Water level was right up to/just over the level of the lower sealing surface of the radiator.

Perhaps Kevin might like to check his as well.

Ian

 

 

[Kevin Atkins]

1 hour ago, Iain T said:

Somefink wrong 'ere! 

The depth on my rad neck is more than from seal to seal on the cap! Therefore the bottom seal stands no chance of pressurising the system?

Iain 

Hi Iain,

Hmm, that does indeed look not quite right. When I measured mine, I don't have any calipers so my figures might have been inaccurate, but the two measurements were very close.

However, I think I might have got to the bottom of this.. and I think it is to do with a radiator manufacturing defect possibly.

I took a spare radiator cap and slightly flattened off one side of the sprung plunger.

Took the car for my usual 3 mile run and on my return, checked the hose and expansion bottle. Hose was not distended, and coolant had been ejected into the bottle as expected - in the attached photo, the masking tape indicates the level before the run.

So I think the issue was indeed the sprung plunger obstructing the expansion outlet in the radiator neck, which suggests to me that the radiator neck diameter is too small.

The question now is whether, having bashed the rad cap plunger with a hammer, is seals properly and coolant is drawn back into the system when it cools.. will let you know of results.

 

Edited July 14, 2023 by Kevin Atkins

[Iain T]

19 minutes ago, Kevin Atkins said:

So I think the issue was as I thought it might be - the sprung plunger was obstructing the expansion outlet in the radiator neck, which suggests to me that the radiator neck diameter is too small.

Kevin, there are big dimensional differences in repro manufacturing. The i/d of my rad neck is 41mm and the o/d of my cap bottom seal is 38mm. So there is a 1.5mm all round clearance. From the bottom of the neck outlet tube to the bottom seal is 6.5mm and the thickness of the cap seal and metal pressing is also 6.5mm but with clearance around the periphery water should still escape. I'll run the engine up to temp tomorrow and do the same check on my bottle. 

One (dangerous) way to check if the system is pressurised is to very carefully release the cap when hot. 🥵

Iain 

Edited July 14, 2023 by Iain T

[Ian Foster]

Kevin

That's interesting, but a bit worrying that you have had to distort the cap to get it to work. I'm not sure the system will pressurize properly like that.

The metal ring of my 13lb cap has a diameter of 38.05mm above the lower seal. The inside of the neck is 40.8mm, so just over 1mm of clearance all round.

Ian

[Iain T]

3 minutes ago, Ian Foster said:

The metal ring of my 13lb cap has a diameter of 38.05mm above the lower seal. The inside of the neck is 40.8mm, so just over 1mm of clearance all round.

Snap! Well almost 

Edited July 14, 2023 by Iain T

[Iain T]

4 minutes ago, Ian Foster said:

That's interesting, but a bit worrying that you have had to distort the cap to get it to work. I'm not sure the system will pressurize properly like that.

Ian, can you measure neck to seal and cap? 

Ta

Iain 

[Kevin Atkins]

8 minutes ago, Ian Foster said:

Kevin

That's interesting, but a bit worrying that you have had to distort the cap to get it to work. I'm not sure the system will pressurize properly like that.

The metal ring of my 13lb cap has a diameter of 38.05mm above the lower seal. The inside of the neck is 40.8mm, so just over 1mm of clearance all round.

Ian

Yes it's not ideal, and the bottom sealing face was also slightly distorted in the operation to flatten, although I judged it wasn't significant at the rubber gasket mating surface, but still something of a risk. I need to invest in some calipers and do some proper measurements! It does look like an issue with tolerancing around rad cap and filler neck though.

[Ian Foster]

13 minutes ago, Iain T said:

Ian, can you measure neck to seal and cap?

Iain

Sorry, could you clarify please. My early post covered neck and cap depths.

Ian

[Iain T]

Ian, it's as my photos in previous post which measures the depths not diameters. This will determine if there is a bottom seal. 

Iain