Quick question (that I may have known the answer to years ago but have forgotten 
): Do our '94 4.0s have a radiator petcock for draining the system? Reason I ask is that I was reviewing my earlier thread re: back-flushing the heater core, and saw just yesterday where Prestone makes a system for (front) flushing the entire cooling system. Seems easier and would be just as effective (right?). 
Iâm a bit worried though in that if there is some gunk in the system it could break loose and clog further up in the radiator instead of coming out the drain. 
Still, if that could happen, I wouldnât think Prestone would incur the potential liability by selling it all this time. 
Check the mount peg on the bottom right radiator. The plastic dowel should be hollow if the drain plug is there.
The sedans have this but I donât remember if the XJS does?
99.99% sure it does not.
The problem with any drain and/or flush scheme is getting the old fluid out but leaving the solids in the rad. Ideally, a radiator drain would look like the drain on the Salisbury diff: A big olâ pipe plug, remove and everything inside smaller than a hammer falls out.
Youâd think that the idea of just disconnecting the lower radiator hose would be better, but youâd be wrong. That hose connects well up the side of the radiator, not at the bottom â at least it does on the V12, dunno about on the sixes. So, about six inches of crud can collect in the header tank before any starts coming out the radiator hose connection. Also, for anything to get to the lower radiator hose, it has to have already passed through the core. Anything big enough to obstruct the core already has done so.
The early XJ-S V12 had a petcock at the lower right, probably the best place to put one since putting one in the upper 1/3 header tank at the top left would be impractical. Jaguar even provided a remote handle so you didnât have to bend over to dump your coolant all over the front subframe and out onto the pavement. Unfortunately, the passage through this petcock was tiny, so crud wouldnât come out, only liquid.
I gutted my petcock, drilled as large a hole through it as I dared, and brazed on a hose barb. Then I connected a short piece of hose directed out the bottom of the car, and plugged the end of the hose. Whenever I wanted to drain coolant, just remove the plug and direct the fluid into a container. I even took to putting the fluid back in if I was only draining in order to clean coolant filters.
Yes, I had the same thing on my SIII XJ6. Handy for draining, but not as you point out much good for flushing. I didnât know that the bottom hose wasnât really at the bottom of the system on the V12, something to look out for.
The I6 radiator has a big ole hose connection at the bottom, drivers side bottom corner of the radiator.
It wonât be neat and clean, but as Kirby mentioned, should be big enough for everything smaller than a hammer to come out.
Just canât believe there have been no tongue-in-cheek answers to the subject question. Some of you usual suspects are slipping.
In England the âpeople that want to protect us from ourselvesâ would ban that word now. For example we use âstopcockâ as a term for the tap that turns off the water to a property. Now we have to call it âstopvalveâ or something so nobody gets âoffendedâ.
Trouble is, if you say âstopvalveâ nobody knows what you mean.
Malc
You said âpetcock.â hehehehehehehe
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Once upon a time I was camped on a beach at a lake here in AZ. (yes we have lakes.) A couple of German gents were camped nearby. Their English was passable, and way better than my non-existent German. They were on a sabbatical from their jobs as mechanics for a shop that does whatever the German-equivalent of the MOT is. They had flow to somewhere in south South America, bought a clapped out Toyota wagon, and were on a road trip to northern Canada. I was insanely jealous. Anyway, they were having carb troubles, and kept telling me they needed a âswimmer valve.â After about four tries I realized that they needed a float! Good times.
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Are you sure they didnât want a âschwimmer walveâ?
Hehehehe
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Spigot, bibb borrowed from plumber talk
There is a tale of some German prisoners that escaped a camp in AZ. Careful planning included road maps. Collected by some subterfuge. They built a canoe, kinda like the Alcatraz escapees. They planned to follow a river as denoted by a blue line to the Colorado and thence to Mexico. Alas, then streams were not always flowig⌠Gulley !
One did escape and found a new life and identityâŚ
Carl
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Errr, as Germans ⌠(and probably not speaking Spanish, at least Latin American-type) wouldnât they kind of stick out there? 
No folks at all at that time in the remote AZ desert. Once in Mexico, language not an issue.
Many Germans spoke good or at least passable English. Probably improved in the camp.
At one time as a soldier my dad was in charge of a guard group for German prisoners that opted to work on farms. Powzer was a word that transcended language issue. Dadâs version. decades later, I got it!!!
Pause! Break time!!!
Carl
At first, I thought it was asking, âPet rock, anyone?â
