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operated by a lever that extended up to just below the upper hose fitting. Evidently, the image of luxury is supposed to
include being able to drain your coolant while wearing a tuxedo. For all this effort and expense, Jaguar couldn’t bring
themselves to provide an outlet out the bottom of the car, so opening the drain valve causes coolant to pour all over the
structures in the area and dribble out wherever the catch pan isn’t. The end of the valve is a spherical shape with a
funny flange, making it rather difficult to attach a hose, but it’s possible with enough determination.
Before you get too involved with that drain cock, let me provide a description of what you’re getting into. The drain
cock itself is a solid brass tapered plug valve that turns 90º from full open to full shut. There is a spring on the bottom
that “loads” the tapered plug to keep it sealed; the seal is brass-to-brass, there are no elastomers inside the valve. There
is also a little diamond-shaped washer that fits on a shoulder with two flats that limits motion to 90 degrees. This valve
is probably repairable from most of its typical failure modes, which is an option you may want to keep open; read on
before doing anything irreversible.
Unscrewing the valve from the radiator may be the first irreversible thing you do. It is not a tapered thread; it is sealed
by a fiber washer. But when tightening down, the valve must end up oriented properly to align with the remote handle.
To accomplish this interesting feat, Jaguar appears to have used two tactics: First, the fiber washer may in fact be two
or more fiber washers, indicating the assembler may have added washers as required to get the proper alignment.
Second, the fiber washers are thick and compressible, so there is some considerable range of tightness that will ensure a
seal; the assembler can tighten until it lines up, and leave it. If you take it out, what do you suppose are the odds that it
will line up properly and seal reliably when you reinstall it? Fortunately, the size washer needed is the same as those
used on many oil drain plugs, so you should be able to obtain a good supply of fibre washers of various thicknesses
from local auto supply houses.
If you decide to go ahead and unscrew it, here’s a tip: the hex size is 19/32”, but if you don’t have a wrench that size a
15mm makes a good fit. It may be helpful to unbolt the fan shroud and back it away from the radiator a bit to permit
use of an open-end wrench, since even a crowfoot won’t work well in this space.
Before you reinstall the drain cock, here’s another tip: The hole in the end of the valve is 5/16” to a depth of about a
quarter inch, and then 1/4” the rest of the way through the valve. With a propane torch, it is a fairly simple matter to
solder a short length of 5/16” OD brass tubing into the end of the valve to provide something to attach a hose to. The
hose can then be routed out the bottom of the car, making draining the coolant a lot neater and easier to collect and
dispose of properly. Since there are no nonmetallic parts inside the valve, you don’t even need to take it apart to solder
on it, but you almost might as well -- it’s only one cotter pin. Something to keep in mind: the radiator moves around a
little on its rubber mounts, the oil lines move around a little with the engine moving on its rubber mounts, and the front
subframe moves a bit on its rubber mounts. Make sure there is adequate clearance around the valve and attachments so
they aren’t subject to impacts or rubbing due to these various motions.
Let’s say your radiator drain valve is toast and you have decided to replace it. Ed Sowell ordered one from Jaguar:
“Problem is, it is not the same as the original, even though the part number is correct. Apparently Jaguar found a new
source. The valve is different in several ways. In fact, the only similarity is that it is a 1/4" BSNB thread, about the
same length. The plug is held with a nut rather than a spring and cotter pin. The important differences are:
The diameter of the bore is 3/16", whereas the original is 5/16". Slower drain time, but would work. Also, with
the original I can jamb a 5/16" plastic hose barb fitting into the outlet to allow coolant recovery (as opposed to
washing down the front suspension and splashing on the floor). With the 3/16" bore, it appears impossible to
attach a hose.
There is a handle instead of the tongue on the stem. Consequently, the extension for above-car operation of the
valve cannot be attached. Very bad. You have to get under the car to operate it, and there appears to be no way to
avoid being drenched when you open it! Could be used, but nobody would want to. Might as well just slash the
lower hose!
Due to the height and length of the handle, it can not be installed in the radiator while it is in the car. No matter
which way I set the handle, it bumps into something, e.g., the sub frame, or the oil cooler line. It might work if it
was screwed in before dropping the radiator into the car.
“I find it had to believe Jaguar would say this was a replacement for the original. They must be blind.”