brian-nz Posted January 6 Report Share Posted January 6 Hi Everyone I recently purchased a new radiator cap for my TR3 as I noticed the old one had a split in the bottom rubber piece. I put the new one on and had major overheating issues. The radiator is out and has been flushed by radiator firm. I noticed that the new cap has a rubber seal in the top and is loose but the old cap has no such seal. They are both 4lb caps. The radiator still has the crank hole and no overflow bottle Should the cap have the rubber seal or not. Regards Brian Quote Link to post Share on other sites
Lebro Posted January 6 Report Share Posted January 6 Check the distance of the bottom seal from the top, the TR2-3 ones are deeper than later caps, & need to be in order to seal the rad. It would be unusual for a correct TR3 cap to have a rubber seal at the top, I have only seen that on the TR4 etc caps which are not so deep. Bob Quote Link to post Share on other sites
Z320 Posted January 6 Report Share Posted January 6 Hi Brian, if the problems started with the new rad cap - so very likely the new cap is the reason. Perhaps it is declared 4 PSI, but is more? Check and compare how strong the springs are, and as Bob explains the length. A rubber seal on top may not be correct, but should not cause problems. When does a higher pressure cap cause heating problems? When a bellows thermostat is fitted. Why? It is filled with alcohol - and sadly gas. The alcohol is vaporizing and its pressure is opening the thermostat. But sadly gas and vaporized alcohol is compressable and compressed by pressure > 4 PSI. This is why the bellows thermostat wants to open, but keeps the way to the rad closed. I had that problem when I tried a bellows thermostat on my 4A with 13 PSI cap. Ciao, Marco Quote Link to post Share on other sites
Hamish Posted January 6 Report Share Posted January 6 Sounds like Bob has the best go- too check and fix with the length of the rad cap. from memory the tr2-(long neck)4 the cap is 1” deep and the later 4? 4a direct to rad cap is 3/4” and should be 4lb. Quote Link to post Share on other sites
Trumpy3 Posted January 6 Report Share Posted January 6 Brian Sounds like your replacement cap is one supplied for a long neck radiator fitted with a recovery system. The top seal is there to retain any fluid that passes the rad cap when the engine comes up to temperature. This fluid is then directed to the recovery container ( normally a plastic bottle of some sort) to be redirected back to the radiator when the engine cools. A number of local members here fit recovery systems as it removes the need to remove the rad cap to check the fluid level. It is this removal that is one of the main causes of radiator leaks and is caused by the stressing of the top tank extension when the cap is pressed down to remove it. The standard TR cap does not have this seal but it should not affect the caps performance. The big problem is that the original radiator is fitted with what is called a long neck radiator. You would not be the first to buy a cap from the local store and suffer the same issues you have. The long/short neck relates the the distance between the lower seat of the rad cap and the top seat. most car manufacturers that used the long neck changed to a short neck in the late 50's early 60's. That is the reason that it is not easy to get a long neck cap, at least here. The long neck caps are available but are normally a order in option. I normally recommend fitting a short neck when the radiator is out for repair. Short neck caps are the norm in parts stores. The TR Register Australia stocks these caps. The problem is that the effective radiator pressure is lower when you fit a short neck cap to a long neck radiator as the spring is not as compressed much as it should be. That lowers the boiling point of your coolant and and you can/will dump fluid when he engine comes up to temp. An overheat is the normal result. Compare your old and new cap. Brian Quote Link to post Share on other sites
Z320 Posted January 6 Report Share Posted January 6 22 hours ago, brian-nz said: I put the new one on and had major overheating issues. Regards Brian Hi Brian from NZ, please be so kind and explain more what you mean with that to avoid guiding you in the wrong direction. Ciao, Marco Quote Link to post Share on other sites
RAHTR4 Posted January 7 Report Share Posted January 7 Hi Brian, It is my understanding that the first TR’s were fitted with a 4lb cap which had an overall depth of 1 inch – out of the box. This was installed in a radiator with the extended header tank which had a neck depth of 3/4 inch. This same type of radiator with the extended header tank was fitted to the first TR4’s which again were fitted with a 4lb cap and at car CT9553 a re-designed radiator was introduced where the extended header tank was deleted, but I have not found any records specifically stating which radiator cap was used – so assume it was still the 4lb cap. However Bill Piggott then tells us that during the latter part of production of the TR4 the radiator cap was changed to a 7lb cap and this change was carried over for all TR4A’s. At some unknown point during the above journey it is apparent from the examples I have checked that the depth of the neck was revised to a dimension 1 inch. Originally the radiator caps were supplied by AC and were highly decorated, however during production and like many other manufacturers, the part numbers were changed or added to, which makes it most important to choose a radiator cap by the poundage and dimensions...! Attached is a photo of a period AC RC4 4lb – 1.1/4 inch radiator cap and it can be seen that the information required to measure the radiator neck was also prominently displayed. I do have a number of different poundage N.O.S. radiator caps available if you get stuck. Regards, Richard Quote Link to post Share on other sites
John McCormack Posted January 7 Report Share Posted January 7 (edited) You can't tell which cap is suitable for your TR3 without checking the neck on the radiator. Your car may have been fitted with a recovery system as described above. I put a recovery neck on my daily driver TR2 radiator to avoid having coolant go everywhere when I over filled it. It isn't now a stock TR2 radiator and needs a recovery cap. Check which radiator neck you have and get the cap to go with it. Edited January 7 by John McCormack Quote Link to post Share on other sites
Black Forest TR3A Posted January 9 Report Share Posted January 9 On 1/6/2024 at 10:03 AM, Z320 said: When does a higher pressure cap cause heating problems? When a bellows thermostat is fitted. Why? It is filled with alcohol - and sadly gas. The alcohol is vaporizing and its pressure is opening the thermostat. But sadly gas and vaporized alcohol is compressable and compressed by pressure > 4 PSI. This is why the bellows thermostat wants to open, but keeps the way to the rad closed. I had that problem when I tried a bellows thermostat on my 4A with 13 PSI cap. Hallo Marco, interesting explanation. Never thought of that. From your experience: Where is the limit/max. lbs pressure for the cap? Would it be possible to fit a 7lbs cap without that prob? Quote Link to post Share on other sites
Z320 Posted January 9 Report Share Posted January 9 55 minutes ago, Black Forest TR3A said: Hallo Marco, interesting explanation. Never thought of that. From your experience: Where is the limit/max. lbs pressure for the cap? Would it be possible to fit a 7lbs cap without that prob? Long or short answer? Quote Link to post Share on other sites
Black Forest TR3A Posted January 9 Report Share Posted January 9 Long - I would appreciate it And I say "Dankeschön" in advance No, let's be serious: Is it really that complicated? Quote Link to post Share on other sites
Z320 Posted January 9 Report Share Posted January 9 (edited) The short answer is: I don’t know. The long allows you to judge about the sense of a 7 PSI cap I answer later this evening Edited January 9 by Z320 Quote Link to post Share on other sites
Z320 Posted January 9 Report Share Posted January 9 (edited) Hi Christian, sorry me, I needed some time to prepare a data sheet. First of all, the pressure in the cooling system is caused be 2 reasons (they do not add): #1 (in short words): - expanding coolant is compressing the remaining air in the system --> pressure growing - less air in the system --> higher / "faster" growing pressure, more air in the system --> less / "slower" growing pressure --> with the rad not overfilled (enough air in the rad) all TR2-TR4 can run without an overflow bottle because the pressure is low - my TR4A also came without an overflow bottle (it should have one), I fitted one, it is always empty - on TR6 very likely that works too (I don't own one and can't test it) #2: - hot fluid in a closed system produces his own steam pressure above the fluid level depending on the temperature - hotter --> higher pressure, colder --> lower pressure Some thoughts: - if you run only 4 PSI the coolant has to be keept cooler, the rad must be bigger (because of the low temperature) - fit a higher PSI rad cap, you can run the rad hotter --> you can fit a smaller rad, or the same rad is more powerfull - not the rad cap produces the pressure, it only limits it! - at for example max 130° a Glykol / water mix 50/50 produces its own pressure of 1.9 bar --> you have to fit a 13 PSI rad cap to limit the pressure See this data sheet, here the black line of a Glykol / water mix 50/50, good for no freezing down to -38°C: Have a look at: 0.8 bar, driving at 2,000 m above sea level with an opened system: the mix will not boil before approx. 103°C 0.9 bar, driving at 1,000 m above sea level with an opened system: dito 107°C 1.0 bar, driving at sea level with an opened system: dito 110°C 1.276 bar because of a 4 PSI rad cap on a closed system: dito 118°C 1.483 bar because of a 7 PSI rad cap on a closed system: dito 122°C 1.896 bar because of a 13 PSI rad cap on a closed system: dito 130°C The answer is: you can try a 7 PSI rad cap (what seems to be nearly double from 4 PSI) and see if it works with the bellows thermostat, but it allows only about 4 Kelvin hotter coolant. Ciao, Marco Edited January 9 by Z320 Quote Link to post Share on other sites
Black Forest TR3A Posted January 10 Report Share Posted January 10 Thank you very much, Marco! Impressive! So when I will have finished my car (with new derusted engine, new radiator, new Bellows etc.) - in 2-3 years - I will try the new original 4 PSI cap and see where I am. I have both AC caps on the shelf: 4 PSI and 7 PSI. With the Black Forest and the Vosges here in the Upper Rhine Valley we have altitudes from ca. 250m up to ca. 1300m; this might be a factor, too... Quote Link to post Share on other sites
Z320 Posted January 10 Report Share Posted January 10 (edited) You are wellcome, Black Forest guy If you want to allow 130° with a 13 PSI cap: kick that bellows thermostat out (in no case buy a new one!), fit a 86°C wax thermostat and reduce the bypass in the water pump housing down to 8 - 8.5 mm. This is what Triumph did with the change from TR2-4 to TR4A and TR6. No real need, a TR2-4 also works well with the original setup! Edited January 10 by Z320 Quote Link to post Share on other sites
brian-nz Posted January 12 Author Report Share Posted January 12 Hi Everyone Thank you for your responses. Just an update - radiator flushed and pressure tested. -water pump removed. The fins still all good however the measurement from fins to water pump face = 17mm. Measurement from housing face to lip = 22mm. This may be some of my cooling issues. The original which I replaced a few years ago due to leaking also measures 22mm. New pump ordered and measured to ensure correct one. Cap is the same one as per Moss and will test without rubber seal. It measures correctly without seal. Regards Brian Quote Link to post Share on other sites
Z320 Posted January 12 Report Share Posted January 12 Hi Brian, Did you change pump and rad cap the same moment. Ciao, Marco Quote Link to post Share on other sites
brian-nz Posted January 13 Author Report Share Posted January 13 Hi Marco No I replaced the water pump a couple of years ago as the old one was leaking. Has run a bit hot since then and this is likely the reason Brian Quote Link to post Share on other sites
Z320 Posted January 13 Report Share Posted January 13 Hi Brian, 3 thoughts: - very likely this is the reason, a 5-6 mm the gay between impeller and housing makes the pump very inefficient - amazing to know it works anyway!! - great you found out by your own skills! The force is with you. Ciao, Marco Quote Link to post Share on other sites
iain Posted January 13 Report Share Posted January 13 On 1/10/2024 at 8:36 AM, Black Forest TR3A said: Thank you very much, Marco! Impressive! So when I will have finished my car (with new derusted engine, new radiator, new Bellows etc.) - in 2-3 years - I will try the new original 4 PSI cap and see where I am. I have both AC caps on the shelf: 4 PSI and 7 PSI. With the Black Forest and the Vosges here in the Upper Rhine Valley we have altitudes from ca. 250m up to ca. 1300m; this might be a factor, too... I have regularly used my car in those regions and also the French, Italian Alps and Pyrenees on navigational rally’s. I have a standard recored (6 years ago ) radiator, a very clean engine and a standard radiator cap. I have a Revotec fan, with their controller and have not had any issues with cooling……..keeping my fingers crossed now. :-) Quote Link to post Share on other sites
Kiwifrog Posted January 13 Report Share Posted January 13 8 hours ago, brian-nz said: Hi Marco No I replaced the water pump a couple of years ago as the old one was leaking. Has run a bit hot since then and this is likely the reason Brian Hi Brian When I restored my 3a here in France I wanted to replace my worn water pump. I ordered one from one of the normal suppliers and it was not much better than my used one so I sent it back. I ended up buying a massey fergerson tractor water pump on the assumption that being the same block it would be the same, it also had a grease nipple fitted as per the original. I had to modify it slightly to fit the TR fanbelt pulley, I still use the wide belt, but it has been fine since then and I have driven the car in temperatures of 40°C in summer with no problems. The other point is that when I had my radiator re-cored I had the starting handle hole deleted. Cheers Alan Quote Link to post Share on other sites
Trumpy3 Posted January 13 Report Share Posted January 13 Hi all, When I was running track work, my TR3A's standard cooling system was not man enough to handle 40+C temperatures. Remember, for every HP you add to your engine is one extra HP you must handle with your coolant system. Ball park figure is for every unit of energy produced in combustion, about 1/3 is converted to mechanical energy, 1/3 out the cooling system, and 1/3 out the exhaust. I now run a Volvo 740 cross flow radiator, no thermostat, and a Davies Craig electric water pump and controller with a electric 14" puller fan. On then track In 40+ ambient temps, the coolant temperature would no go above 90C. The down side is in winter I have to refit the thermostat to get the temps up. Not sure how you would go over there considering the temperatures you see in winter.. Brian Quote Link to post Share on other sites
Nigel C Posted January 21 Report Share Posted January 21 Going back to rad/header tank caps, I have a bespoke header tank (due to room/access etc) and I have measured the depth of the fitting as 3/4". I have been using a 4lb cap that measures 1" from bottom rubber seal to top rubber seal. you have to depress the cap it get it to latch onto the fitting and then turn. Is this correct or should the cap also measure 3/4"? Could this set up actually affect the pressure rating of the cap as it is being compressed more than it should or am I just over thunking it! From this cap/fitting I have a "puke tank" so it can discharge all it likes and suck it back when cold. Quote Link to post Share on other sites
Lebro Posted January 21 Report Share Posted January 21 The 1" compressing to 3/4" sounds exactly right. Bob Quote Link to post Share on other sites
Nigel C Posted January 21 Report Share Posted January 21 8 minutes ago, Lebro said: The 1" compressing to 3/4" sounds exactly right. Bob that's what I thought but when working on your own you do start to question yourself Quote Link to post Share on other sites
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