Radiator cap question
 

Part mja4440BA
one of these caps the complete interior section of the cap rotates freely and on the other cap it’s fixed. Which is correct please? Both caps in good appearance and same part number!

Correction
 

I am referring to the expansion tank cap...

Alan, if no one answers I'll take a look tomorrow at mine.

John

Checked my spare and it rotates freely.

Both my original 1998 and its 2020 replacement also rotate freely

Expansion tank cap - the internal bit should rotate freely. The insides of it are is actually calibrated to allow coolant to go to the atmospheric tank. If it's stuck and doesn't rotate, you may have problems.

These caps all seem to have a limited lifespan before they fail to function properly. Now at more than 9 years of vehicle ownership, my wife's 2006 XK8 is currently on its fifth cap. OEM appears to last longer than the various aftermarket versions (which are significantly less expensive)....

I have no explication why my original cap is still functioning after 166,000 miles and 20 years.

I’m just not that lucky (usually).


Z


PS. in other nonessential news, my shocks and their bushings have 7 years and .52,000 miles on them and appear to be doing OK too.