The short answer = NO!
We strongly recommend you read this technical note BEFORE adding coolant sealant to your classic Jaguar XJS. We’ve had several cases where the consequences have caused severe (and expensive to repair) damage.
In the note we explain how sealants work and describe the complex process we’ve devised to flush it out.
We also give advice on what you should do if you have a coolant leak – a must read for all classic Jaguar drivers.