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Radiator Cap

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TRMark

TRMark

Jedi Knight
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I think this discussion has occured before, but I could not find it using search. The radiator cap I bought from one of the Big Three fell apart into my radiator. Couldn't get to the part so I had to remove the radiator turn it upside down and shake to get to it. Not amused. Anyway the various TR supplier catalogs list the cap as 7 lb. as was the one that fell apart. When I look up the appropriate cap at Stant or NAPA, they show 4 lb. as does my repair manual. What's the deal? While the radiator is out I am switching the electric cooling fan from pusher to puller, so not a total waste of time.
 
Hey, Mark, from what I understand, the 3 used a 4 lb cap, but since the heater core was improved on the 4, it could take more pressure and used a 7 lb. These auto stores probably don't know the difference between the two models, you suppose?

Fred
 
I agree with Fred, I put a 7 lb cap on my TR4 a few months ago, but unfortunately I do not have specifics on what I ordered - it wasn't a Stant or NAPA.

The caps are pretty easy to source over here in the UK, unfortunately the other cars they fit I don't think are too common in the U.S. either. Here's a recent ebay link showing some cross references:

ebay.co.uk radiator cap

Randy
 
Thanks for the replies. What got me curious is my workshop manual, published in 1965, lists a 4lb cap. The pressure testing procedure in the manual uses 4lb of pressure. I'll try to find either a 4 or 7 locally, hopefully it won't fall apart.
 
TRMark,
There has to be a "good" rad repair shop in or near Billings that could get you a cap or tell you how to calculate the cap pressure based on the volume of the rad and the system????
I just found a whole wack of rad repair shops by doing a Google Maps search under
Radiator repair, Billing Montana
 
If you still want to check the old thread, Mark, it is called Radiator Pressure Cap and was started on 7-11-05 by bluemiata90 in post #79688.

Fred
 
Hi Mark,

The previous posts are correct. TR4/4A use a 7 lb. cap.

In addition, another thing to watch out for is that the length of the cap changed at some point during TR4/4A production. That is, the depth of the flange on the top of the radiator neck changed, and the cap was changed to fit it. There are two sizes. Early used a 1" depth, later uses 3/4".

To make it a bit more complicated, sometimes when radiators are rebuilt a new neck might be installed. And, sometimes this is a more modern 3/4". So, even an older rad can have the later style neck.

I suggest you measure the flange on your radiator to see how deep it is, to be certain. The measurement might not be given on the packaging of the caps in the store, so a tape measure can be handy to have there, too.
 
i got a 7 lb cap for my '59 TR10 from John Paddock auto parts (in the UK). It was reasonably priced and took less than a week to arrive from order date. The also had the correct heater return pipe for my engine, slightly different than the pipes used in the spitfires with 1147 engines.
 
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