Ian Foster Posted July 14, 2023 Report Share Posted July 14, 2023 Iain Radiator neck is 19.05mm deep from top surface to lower sealing surface. The cap (7lb) is 20.2mm between the two seal surfaces. My spare 13lb cap is 19.4mm. Ian Link to comment Share on other sites More sharing options...
johny Posted July 14, 2023 Report Share Posted July 14, 2023 To test my system cold I pressurise it using a foot pump connected to the overflow pipe so air is pushed in via the caps vacuum release valve. Have to be careful to use the gauge not go too high as of course the cap wont lift to protect things but you can then leave it for a while and check to see if pressure has been lost. NOTE that when removing the cap coolant will spray back out as although not hot its messy cos it can shoot out like a fizzy drink! Link to comment Share on other sites More sharing options...
Iain T Posted July 14, 2023 Report Share Posted July 14, 2023 Thanks Ian my neck is deeper and the cap very similar to yours. Perhaps the simplest way to rectify would be an additional rubber washer placed on the rad neck seal face. I'm not sure a say 1mm steel ring would seal. More testing tomorrow! Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 14, 2023 Report Share Posted July 14, 2023 1 minute ago, johny said: NOTE that when removing the cap coolant will spray back out as although not hot its messy cos it can shoot out like a fizzy drink! Been there several decades ago! Link to comment Share on other sites More sharing options...
johny Posted July 14, 2023 Report Share Posted July 14, 2023 Also I see radiator caps for Triumphs also come in a 1" deep version as opposed to the 3/4" recommended for the GT6 so wonder if one of these would be better in your case.... Link to comment Share on other sites More sharing options...
Iain T Posted July 14, 2023 Report Share Posted July 14, 2023 3 minutes ago, johny said: To test my system cold I pressurise it using a foot pump connected to the overflow pipe so air is pushed in via the caps vacuum release valve But this doesn't check the first lower seal? Link to comment Share on other sites More sharing options...
johny Posted July 14, 2023 Report Share Posted July 14, 2023 It does if you disconnect the pump as then the system should just sit there pressurised until you remove the rad cap... 1 Link to comment Share on other sites More sharing options...
Iain T Posted July 14, 2023 Report Share Posted July 14, 2023 4 minutes ago, johny said: Also I see radiator caps for Triumphs also come in a 1" deep version as opposed to the 3/4" recommended for the GT6 so wonder if one of these would be better in your case.... I think 1" would be too deep. It's the Bastuck rad that's at fault. Iain Link to comment Share on other sites More sharing options...
johny Posted July 14, 2023 Report Share Posted July 14, 2023 Hmmm that doesnt surprise me with Bastuck.... Link to comment Share on other sites More sharing options...
Ian Foster Posted July 14, 2023 Report Share Posted July 14, 2023 10 minutes ago, johny said: radiator caps for Triumphs also come in a 1" deep version as opposed to the 3/4" recommended for the GT6 Didn't know that. I suppose this is an option, but it might be better to use a 7lb cap on a 13lb system, as the additional compression would increase the effective spring rate. Ian Link to comment Share on other sites More sharing options...
Iain T Posted July 14, 2023 Report Share Posted July 14, 2023 I agree I don't want to over pressurise the system. It's old like me! Iain Link to comment Share on other sites More sharing options...
johny Posted July 14, 2023 Report Share Posted July 14, 2023 yes probably best to check the lift pressure with the foot pump as on disconnecting it the cap will liberate any excess pressure. Then when you pump again the reading you get when air starts to re-enter the rad will be what the cap closed at... Link to comment Share on other sites More sharing options...
Iain T Posted July 15, 2023 Report Share Posted July 15, 2023 (edited) 23 hours ago, johny said: To test my system cold I pressurise it using a foot pump connected to the overflow pipe so air is pushed in via the caps vacuum release valve. Firstly my apologies Kevin for hijacking your post. Test result in. Using my foot pump I attached it to the overflow pipe. Gave it a few pumps and noticed a few drips out of the top hose to rad joint and hence no pressure. Tightened the clamp! Tried again and got up to 10psi but it reduced to zero in less than 30 seconds. Unplugged pump and no pressure in the overflow hose. I then carefully undid the rad cap (note the system is cold) and air and fluid gurgled down the overflow hose. Is it the top cap seal that is leaking? What seems to happening is I've pressurised the coolant system from the wrong side. I'm unsure how that could happen if the bottom seal is working correctly. There was definitely pressure when I release the cap so the bottom seal was doing something. Next test is to see if any fluid rises in the overflow when the engine is hot. Just read Johnny's post, there's a vacuum release valve? Hmm, I'm not twiddling anymore today as I'm driving to Brands tomorrow for a historic race meet and I don't want to prod the Gods! Any thoughts? Iain Edited July 15, 2023 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 15, 2023 Report Share Posted July 15, 2023 More googling and I think my system is working sort of correctly as I pressurised the system via the vacuum release valve as evident when I opened the cap. The fact that it didn't hold pressure could be down to the top seal? Iain Link to comment Share on other sites More sharing options...
johny Posted July 15, 2023 Report Share Posted July 15, 2023 It is asking a lot of the top seal I suppose as in service it only has to seal well enough to allow the vacuum generated by the cooling system to pull coolant back from the reservoir bottle. I can certainly get and hold quite a good pressure in my radiator/overflow pipe however I have an aftermarket aluminium rad with a miniature Japanese style rad cap... Link to comment Share on other sites More sharing options...
Iain T Posted July 15, 2023 Report Share Posted July 15, 2023 Thanks for your help Johny, at least I found a leak and know more about the workings of the rad cap! This is all essential information to bore the wife with....... Iain Link to comment Share on other sites More sharing options...
johny Posted July 15, 2023 Report Share Posted July 15, 2023 ha, ha good luck with that one! In the end it comes down to how it runs and if coolant gets expelled and drawn back in satisfactorily - something which Ive sometimes found quite difficult to achieve because of small leaks usually where hoses attach🤪 1 Link to comment Share on other sites More sharing options...
Iain T Posted July 15, 2023 Report Share Posted July 15, 2023 9 minutes ago, johny said: something which Ive sometimes found quite difficult to achieve because of small leaks usually where hoses attach🤪 We'll this celebratory beer could pressurise the system. A very nice tipple and only 3.4% alcohol. Link to comment Share on other sites More sharing options...
Kevin Atkins Posted July 15, 2023 Author Report Share Posted July 15, 2023 4 hours ago, Iain T said: Firstly my apologies Kevin for hijacking your post. No worries at all on that Iain - it's all in the same ballpark, we both seem to be struggling with issues around the rad cap / radiator neck interface 😜 My butchered (erm, hammered..) rad cap kind of worked OK but I wasn't sure it was sealing to the rated pressure - too much coolant seemed to be expelled into the expansion bottle.. I put the other, non-butchered rad cap on and ran straight back into the original problem. For now, I have tweaked the butchered cap and straightened out the seating surface and it seems to be working correctly. I'm going to have a go at drilling some small holes around the lip of the lower plunger on another rad cap, so as not to distort the plunger, and see if that works.. I also got some calipers through from Amazon and did some measurements - from what I can determine, there should be around 1mm clearance between the sprung plunger and the inside wall of the radiator neck, but for whatever reason, the plunger does appear to be obstructing the overflow outlet.. PS - Nice choice of beer Iain - haven't tried that one, but I have fond memories of St. Austell beers from holidays in Cornwall, love that part of the world! Link to comment Share on other sites More sharing options...
GrahamB Posted July 16, 2023 Report Share Posted July 16, 2023 After reading another thread and looking at the earlier photos, it would appear that the soft top hose with no reinforcement is not fit for purpose; easy to fit but not sufficiently rigid. It is just bulging at 13 psi as it is too soft. This could be taking up most of the expansion in the cooling system. I would replace it with a reinforced version, as I believe you intend to do, and then see how it operates. 1 Link to comment Share on other sites More sharing options...
Colin Lindsay Posted July 16, 2023 Report Share Posted July 16, 2023 5 hours ago, GrahamB said: After reading another thread and looking at the earlier photos, it would appear that the soft top hose with no reinforcement is not fit for purpose; easy to fit but not sufficiently rigid. It is just bulging at 13 psi as it is too soft. This could be taking up most of the expansion in the cooling system. I would replace it with a reinforced version, as I believe you intend to do, and then see how it operates. I'd agree; this was a brand new one last year, and it lasted ten miles in the Herald. An older reinforced hose replaced it, and has lasted ever since. Link to comment Share on other sites More sharing options...
Kevin Atkins Posted July 16, 2023 Author Report Share Posted July 16, 2023 Yes, that hose is getting binned as soon as I receive the reinforced one! That said, I think there might still be an issue with the radiator neck overflow - my 'tweaked' radiator cap now seems to be operating as intended, and the hose isn't bulging.. maybe a reinforced hose might disguise the issue but if coolant can't expand out of the cap, I'm mindful there might be a risk to the next weakest link in the system, which could be radiator or heater matrix cores? I might experiment with the foot pump method described earlier, I need to get a handle on exactly what is happening, if only for peace of mind! Link to comment Share on other sites More sharing options...
Iain T Posted July 16, 2023 Report Share Posted July 16, 2023 A hot 30 minute traffic jam at Blackwall tunnel coming home from Brands and with the electric fan on manual the water temp was 75-85C. I was 110C! Kevin as long as you have water exiting to the overflow bottle and then being drawn back I wouldn't worry. If the temperature gauge stays around normal even better! Iain Link to comment Share on other sites More sharing options...
daverclasper Posted July 16, 2023 Report Share Posted July 16, 2023 (edited) On 12/07/2023 at 18:18, Gully said: Mind you, it's unlikely - main issue I had was finding a cap deep enough! Do you know who supplied it please gully. Same issue on mine (though Vitesse). Currently using a rubber washer and about a 5mm thick washer to reduce the depth. Maybe not sealing where it should, as have empty section/sections of overflow hose always. No problems with overheating, even when really hot ambient temp and traffic jams, so not the end of the world I guess? Thanks, Dave Edited July 16, 2023 by daverclasper Link to comment Share on other sites More sharing options...
Kevin Atkins Posted July 16, 2023 Author Report Share Posted July 16, 2023 1 hour ago, Iain T said: Kevin as long as you have water exiting to the overflow bottle and then being drawn back I wouldn't worry. If the temperature gauge stays around normal even better! Thanks Iain, yes water is being expelled into the bottle and drawn back in on cooling now. Had a couple of good runs today, and it's been quite a warm day; temperature gauge is exactly where it's always been, just around a quarter, creeping up slightly in heavy traffic. The cooling system now seems to be working correctly! Took a mate to the Capesthorne Classic show up here - there have usually been one or two GT6's attending, sadly none today, although there was a particularly nice Spitfire - 1966, never restored, exactly as it left the factory.. it put the panel gaps on my baggy GT6 to shame! I think my mate was a bit unsettled by the symphony of rattles, squeaks and general racket my GT6 makes.. there's certainly room for more improvements, but she'll never be a show queen, nor anything approaching 'modern' refinement... which is all good with me 😜 Link to comment Share on other sites More sharing options...
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