2004 XJR a couple weeks ago fan would spin for some time so we have replaced thermostat and temp sensor.
For a few days everything was working fine but in addition to recurring spinning fan, we now have got new
overheating problem.

It looks like new sensor and thermostat wouldn't fix problem but created even bigger one. Removing thermostat
have stopped overheating but fan is still spinning for another 3 - 5 minutes. It's hard to believe that both middle priced parts purchased parts Rock Auto would be bad and/or get bad in the same time

Any ideas, please.

 

I think you need to burp the system - you may have an air pocket. It actually sounds like the system is now working, but an air bubble would cause your problems.

 

Funny you have mention. When we have replaced thermostat, we've added up to top antifreeze reservoir, at least
one and a half gallon, let car run till water start moving, bleed tank and supercharger but somehow reservoir was
half empty this time. As I have mentioned, everything was working fine for some time.

I guess my question is, where gallon and a half of antifreeze went, no pool found?
Is it possible to have air packet given we've bleed system?

 

Some have had similar problems on the forum which were resolved by properly bleeding the system. Not sure on the super charger variant as I am not familiar w them. Do some searching on tricks people use to burp the system. I recall one guy parking on an incline to resolve his problem.

 

Many people do place the car with the nose up when bleeding the system.

You also have to run the engine with the heat on high for a time to properly bleed the system.

The "only" sure way is to initiate a vacuum to properly draw out any trapped air.

 

P38 Range Rovers are the worst to bleed. Worst trapped air nightmare. Jackra is right. The foolproof way is to vac the system , and refill. Most newer cars have air pocket issues, and are bleed by the dealers using vac. This was one of the best tools I've purchased (airlift) , as I will use it on all my future cars as well. Also with this there is NO mess, no funnels, and fast. The vac will also confirm "no leak" status.