Jaguar XK8 and XKR convertible top hydraulic problems

I’ve written a few articles about the issues with Jaguar XK8 Convertible top hydraulics over the years.  I’d like to begin by referencing Jaguar’s own technical service bulletin on this topic -

TSB 501-33 -  1997-1999 Convertible Top Operating Slowly - Amended April 2003

Issue: early XK8 Convertibles may experience slow operation of the convertible top, or slow or erratic operation of the latch. These conditions are caused by a tendency of the Univis hydraulic fluid in the system to slowly evaporate, and in certain conditions to gel within the hydraulic system pipes and hoses. From VIN 037189, vehicles in production have been filled with an improved fluid, Pentosin CHF 11S.

The service bulletin informs us that the fluid may gel, and the top may stop operating as a result.  On the face of it, the story sounds pretty benign.  Lately we have seen things take a turn for the worse.

During the past six months three early XK8 Jaguar convertibles came into Robison Service with slow convertible top complaints.  Two cars were leak free; the third was showing the familiar hydraulic oil drip from the header bar.  On each car we found original fluid in the top hydraulics.  Two of the cars were still in the hands of original owners, and the third had been owned by its current owner since three years of age. All were certain – there had never been an issue with the top before.

After changing to CHF11S fluid (and in one case, changing leaking lines) all three cars developed additional leaks from the ram seals and lines.  Why did that happen, we wondered? 

A close examination of the failed parts offers some answers.  The first clue can be seen in one of the pump reservoirs, shown after thorough flushing and change to CHF11S fluid.  You can see the fresh CHF fluid as green liquid in the bottom of the reservoir.  Above that, lining the bottom of the reservoir, you see a slimy mix of the two fluids.  At the front of the reservoir is a hard lump of what started out as Jaguar hydraulic oil, circa 1998.

We already know the old hydraulic fluid was prone to thicken and solidify in chunks.  What we now know is that those chunks get into the seals of the rams and latch, and chew them up.  But they do not always leak, because the chunks of congealed oil act as leak-plugs, which means the problem worsens with age, while remaining invisible.

All that changes when the fluid is flushed.  All of a sudden you have thin, fast moving oil flowing through the system.  As the chunky old fluid is washed away, leaks appear.  The solution:  Replace the lines, rebuild the rams, and rebuild the latch and pump.  All the chunky old oil has to go, as do all the seals, and total rebuild is the only way to accomplish that.

My takeaway from this:  Change your hydraulic oil, just like any other fluid.  It was the chunky deteriorated fluid that caused the seal damage.  If these cars had gotten top fluid services every five years, there is a good chance this total failure would not have happened.  Having said that, I must also point out that many carmakers (Jag included) use plastic hoses now, and those get brittle and fragile no matter what’s in them.

The lesson for owners of pre-2000 XK8 convertibles:  If you have trouble with the top, be prepared for the possibility of leaks after flush, and if that happens, rebuild the whole thing and have done with it because the alternative will be replacing everything one part at a time, which will cost you a lot more in the end.

John Elder Robison is a NY Times bestselling author and the founder of J E Robsion Service of Springfield, MA.  Robison Service is a long established Jaguar service specialist, with expertise in postwar Jaguar motorcars from 1950 to the present day. Find them online at www.robisonservice.comor in the real world at 413-785-1665