Am still baffled,discovery 3.9 v8 thermostat sealing ring.I got two different sealing rings with my new thermostat.When i took the old thermostat out,there was'nt any seal on it.Does the v8 have one on it.

Seems that you have an after market thermostat supplied with a seal for any application that needs one, but in my limited experience on fitting thermostats it's metal to metal and a seal isn't required, after all it doesn't need to be completely water tight especially if it's fitted with a jiggle pin.
I have a clue on a 3.9 but a 3.5 doesn't use a seal of any sort.

No seal, just gasket or sealant and right way up