i do add new coolant to my S1 , have you some guidelines / brand /tech data ?
Fred
Any decent green stuff: just make sure to use good water (not hard), flush the system, make sure it is up to spec, and you’ll be golden.
This assumes the system is clean, the radiator is not plugged, the head gasket is not corroded, the water passages are also not corroded, and the head studs are not rusted: many of these things WILL occur in almost any 30-40 year old Jag.
thank you Paul,
radiator, hoses, water pump are new and 100% dry.
Readed about “without water cooler” and “Water wetter” miracle additive.
i’m terribly worried about my delicate 2.8 engine …so this “spot” found me soft…
what you think? are spot only?
Fred
thank you
Not sure I understand: “are spot only?”
Water Wetter is NOT a miracle drug! Just good, soft water and good brand green antifreeze, in a 50/50 mixture.
I have exatly your idea, however many classic owners confirm are miracle drugs!!
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Fred,
Many classic cars owners do not know what they are talking about.
Paul
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Google Water Wetter brown sludge/slime
If freezing is not a problem, check out www.norosion.com especially the Tech page.
On the XJ-S, I recommend that about every two years – roughly coolant change intervals – the radiator be removed from the car completely. This is simply to clean the fins, especially near the bottom, which get plugged up with grass and dead bugs and is impossible to clean with the radiator in the car. Removal is relatively easy. I presume the same advice would apply to the XJ12. If the radiator hasn’t been removed for cleaning in memory, it’s definitely a good idea.
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For now it’s new and a 2.8 so if it is driven hard and the coolant renewed every two years or so it should be fine. The 2.8s are said to suffer only when driven gently but should be very strong when exercised from time to time.
Green, 50:50, change from time to time.
David
you’re definitly nr 1 Paul ! 
Thank’you all!
David i know what you tell… and i’m doubt…
broke appear using engine up after many km used low…
Last user was in 1987…so , what i do ??? slow or full speed ahead at maximum RPM ?
Here, somebody on the XJ-S forum posted a photo showing why the radiator has to come out:
Low RPM, lots of load probably? I would not give it high rpm (that saying about the ridge in the cylinder bore that develops over time), and if at all carefully increase engine speed. Full throttle though.
But from what everyone is saying the problem of the 2.8 is the carbon buildup melting the pistons, and that Jaguar didn’t find out in testing because they did not test for careful, slow city driving.
So I would certainly use it to its full potential, given its age probably not at full engine speed. The engines are strong and can take a lot. I don’t know how the bore wear situation is in the 2.8, and it should depend on mileage.