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Standard on Canadian cars. Here is another photo of one in the lower rad hose.
XK engines have a boss on the side of the block to accept a screw in element, XJ40 and X300 sedans have the boss moulded right into the lower rad hose.
I fitted one to my AJ16 XJS just because Jaguar sold some off dirt cheap. I think I wrote a thread on it here(?) I monitored the cylinder head temps as it was plugged in.
My general conclusion was that it provided some benefit in warming the coolant somewhat but,without a pumped system, could not really get the engine that warm. Still, anything that helps the warmup process even a little bit can only be a good thing in reducing engine wear.
I fitted one to my AJ16 XJS just because Jaguar sold some off dirt cheap. I think I wrote a thread on it here(?) I monitored the cylinder head temps as it was plugged in.
I had a block heater in my 3.8 E Type and it made a noticeable difference to cranking speed and how fast the engine started below 10 degrees. I'd plug it in for about 45 min to a hour before I wanted to go anywhere. The cam covers did get warm to the touch, but the heater was also in the block water jacket, not in a hose.
I think thats the real difference. I'd suggest a true block heater will have much impact on the temp of the coolant circulating the block and head. My lower hose heater is relying on a simple transference of heat all the way up through the hoses into the engine.
I think the best way is to use a heater and pump system such as the Kenlowe ones. I put one of those on my daily driver classic Range Rover some years ago. It worked great and also gave me instant cabin heating when I drove off! With the privileged life my XJS now has, I dont think I could be bothered to fit that type now.
