Hey yall forgive me for invading I have an XJ12 not an XJS V12. Anyway I'm changing the water pump and radiator. So in regards to the water pump I have every bolt off except this guy which is at the bottom just above the crank pulley. What is it? I'm not familiar with this head. Thanks.

 

That is a Pozi-Drive Screw... As is nearly every other "phillips head" looking screw on the car.

 

Specifically, it's a Pozidrive #3. You need to get that specific size driver, or you risk cammng it out. Do NOT try a large Phillips driver; won't fit right. I got a 1/4" hex drive bit. Search for "PZ3 bit". You can also find screwdriver type sets, such as this on Amazon.
http://GEARWRENCH 4 Pc. Pozidriv Dua...a.co/d/8A450MN

Edit: corrected size

Jon

 

It is a Pozi size 3. Do not use anything else!
This is what you need

 

You're correct on the size. I revised my post above.

 

Cheers thanks. BTW do you have any idea on what I should use to undo those hard metal lines that connect to the top (just beneath the upper radiator hose) and bottom of the radiator. I think they are transmission cooler lines but I could be wrong.

Box ends don't fit right and neither do adjustable crescent wrenches.

 

Yes, I wasn't sure of the size from the photo (and I was not near the car today), but Pozi3 makes sense. My advice would be to "get the whole set", or at least the drivers for size 1, 2, and 3. You will use them a LOT. Especially the size 2.

 

I just did the water pump on mine; had no issue using a #4 Phillips bit. But I will say that the pump had been replaced prior, and that the screw did not have the Pozidrive indicating marks on it’s face, so could have been replaced.

 

The way to tell a pozi is the look for the marks at 45 degrees. It's a reasonable assumption that everything "phillips" on a Jaguar is actually pozi.

 

Ok thanks for the heads up. This Jag V12 stuff is new to me and I'm learning every day I am working on it.

 

The one in your photo is definitely a Pozidrive, as you can see the Pozidrive marking; my point was to make no assumption on a car 35+ years old, as someone was likely there before you…..
Both the Pozidrive and Philips are available in the 5/16-18 UNC thread, and some of the V12 water pumps are not machined for a countersunk head and use a regular hex head bold.

 

I use these on tubing. You don’t need to use Snap On, Harbor frieght has these at seriously lower cost. They are both decent and affordable