Radiator cap pressure

[Bluebottle]

I have a 1963 3.8 FHC #888279. My radiator cap self-destructed and I need to replace it. What pressure rating should I order? Mine is 9lbs., but I have found 4lbs, 7lbs and 13 lbs so far, not 9lbs - which is correct for my car? Thanks for your help.

[DWW]

7ib on my header tank.

[Series1 Stu]

According to the parts manual, your car should have a 9lb pressure cap. They changed from 4lb to 9lb starting at car number 888241. They are available, just be sure to get the correct length reach for your header tank.

Not sure where Danny got the 7lb figure from.

Regards

[paydase]

What did Jaguar change to accomodate the new 7 lb pressure: only replace the big convoluted hose on top right of the header tank by a non convoluted one?

[Gfhug]

The radiator caps changed between the 3.8 and 4.2 and between S1 and S2 because of different radiators.
On the S2 4.2 the pressure cap goes on the expansion tank NOT the radiator which has a plain cap. Isn’t this the same for the 3.8?

Geoff

[mgcjag]

Lots of cap info here..but read right through... Steve viewtopic.php?f=4&t=13898&p=113728&hili ... ap#p113728

[Series1 Stu]

9lbs

[mtnjag]

3.8 radiator doesn't have a cap at all. I run a 7# with my bellows style thermostat.

[mgcjag]

Hi Layne....the 3.8 has an expansion tank on top of the radiator...the Service manual and service bulletins refer to its cap as a radiator filler cap.....if your running a bellows thermostat than you should be useing a 4lb cap...higher pressure affects the alcohol in the stat and its operation.....Steve.....ps you posted not long ago that you were useing a sleeve type thermostat..

[mtnjag]

No expansion tank or cap on top of my radiator. But we may be talking semantics here.

Stock crossflow rad with the expansion tank separate from the radiator up and to the rear of radiator.

Yes, a repro sleeve thermostat I bought from Moss (XKs back then) around 1990. I have read good for a 7# cap. Been working well for all this time. I did say bellows which was an original style with the sleeve. Haven't seen it for 35 years so I should be a little vague on that. It does work with a sleeve to block the bypass when it opens.