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Radiator Cap Size


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After reading numerous threads from members about their TR's running hot, I thought this little exercise I have just completed might help!

 

Having satisfactorily run my restored 4 with a long necked radiator and 4lb cap for the last two years, as preparation for a 3,000 mile run to Southern Spain and back in Sept I thought it would be a good idea to raise the boiling point by fitting 7lb cap.

Checking the TR parts suppliers catalogues, I was informed I would need a "1" depth, 7lb cap" to fit my rad. This was ordered and fitted and then my troubles began.

The hoses went rock hard and the rad sprung a small pin leak from a soldered area, but most interesting of all the temp gauge went from it's usual position of just right of centre (N), to just short of the red H :( .

Obviously it was the new cap <_< , so examining it closely, it appeared to be the same size as the old 4lb cap I had replaced, but the internal spring had to be compressed with rather more force than I had been used to, albeit from an old weakened cap.

After giving this some thought it occured to me for the 7lb pressure spring to work as a 7lb pressure valve it shouldn't need compressing at all, and in doing so I couldn't imagine the extra blow-off poundage I had created, obviously greater than my waterworks could stand.

I consulted a friend (who has restored MG's for years) and he produced an old tatty Quinten Hazel parts book. The book listed a Rad Cap for TR4's, part No FC43A. This was a stock item from our local factors and was promptly fitted :D .

Surprise, surprise, the bottom seal was a snug fit on to the fill neck with no spring compression necessary.

I have now driven the car for 50 miles and the hoses are firm, the temp gauge is back to it's normal place just to the right of normal. and the pin hole is fixed with 25gram of Barseal.

BTW, having put a multimeter thermo-sensor on to my thermostat housing the car runs at 71dg c, so it appears that most temp gauges are well off calibration anyway.

I would appreciate some feed-back about the running temperatures of a 4, not being very knowledgeable about thermo dynamics inside an engine.

Phil

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After reading numerous threads from members about their TR's running hot, I thought this little exercise I have just completed might help!

 

Surprise, surprise, the bottom seal was a snug fit on to the fill neck with no spring compression necessary.

I have now driven the car for 50 miles and the hoses are firm, the temp gauge is back to it's normal place just to the right of normal. and the pin hole is fixed with 25gram of Barseal.

BTW, having put a multimeter thermo-sensor on to my thermostat housing the car runs at 71dg c, so it appears that most temp gauges are well off calibration anyway.

I would appreciate some feed-back about the running temperatures of a 4, not being very knowledgeable about thermo dynamics inside an engine.

Phil

 

 

Phil

 

I don't know about , "not being very knowledgeable". I found your little story very interesting. <_<

 

My '62 is running a standard 4lb cap and being a TR4 (not a 4a) it had no expansion bottle so that seemed like a reasonable place to start. Couldn't see the sense in dumping coolant on a long hot trip where supplies might be limited on route. :blink:

 

However, only a few sunny UK days and a brief run down to DiJon in June to try her out, no problems so far. Hoping for better weather and a chance to test her for real on a trip down to Angouleme for the ramparts race in September :lol:

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Hi Mike,

Your standard 4lb cap is presumably a 1" to fit the "long necked" radiator which is what I replaced with a 7lb. As a matter of interest, is it 1" deep? and if it is, does the spring need to be compressed to attach the cap to the rad?

 

I hadn't heard of the "Circuit de Remparts" until you spoke about it and I Googled it! Sounds like a fun weekend, it's a pity my itinerary puts me around Valencia/Barcelona then. I think there would be trouble from the passenger (my wife) if I suddenly set a new course to Angouleme! O well, there's always next year now I know about it :rolleyes:

Phil

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Hi Mike,

Your standard 4lb cap is presumably a 1" to fit the "long necked" radiator which is what I replaced with a 7lb. As a matter of interest, is it 1" deep? and if it is, does the spring need to be compressed to attach the cap to the rad?

 

I hadn't heard of the "Circuit de Remparts" until you spoke about it and I Googled it! Sounds like a fun weekend, it's a pity my itinerary puts me around Valencia/Barcelona then. I think there would be trouble from the passenger (my wife) if I suddenly set a new course to Angouleme! O well, there's always next year now I know about it :rolleyes:

Phil

 

 

Hi Phil

 

No, It doesn't need to be compressed just screwed on as normal. Don't take it off now I have the expansion bottle :lol:

 

Meanwhile, maybe see you at Angouleme in 2008 ;)

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However, only a few sunny UK days and a brief run down to DiJon in June to try her out, no problems so far. Hoping for better weather and a chance to test her for real on a trip down to Angouleme for the ramparts race in September :lol:

 

Mike,

 

I might see you in Angouleme, I am hoping to make it this year and I live just round the corner If I spot your car I will introduce myself. Do not have any roadwortht Triumphs myself :(

 

Cheers

 

Alan

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