Your V6 probably had a fault so it's unwise to use that as a comparison.

Your V8's fan (air conditioning off) will not run until the coolant reaches 99˚C. This should happen only when moving slowly or stationary in traffic for a period of time.

Regarding joining the trinary switch wires to test the faster fan speed, before posting I checked the V8 wiring diagram and that circuit is identical to the other engines so there is no problem there. However I would recommend that you monitor your actual coolant temperature whilst driving and check that the expansion tank isn't overfilled.

Simon

I would get this checked by someone who knows and understands how the V8 system works and who has a T4 if you are still not sure how to proceed with this,Please feel free to contact me and I will run a T4 session and check it for you if you ever come up to Lincolnshire as bridging wires on a V8 is not a good idea

Dave

Fan working. Just like that. However, I think a t4 session is in order before I become too excited. Thank you all for your helpful advice and comments.

From memory as it's been a while since I've had a V8 on T4, that Hevac diagnostics are disabled so a T4 session may tell you very little.

V8 diagnostics especially with the ECM is a bit of a lottery at the best of times too, sometimes they communicate with T4, sometimes they won't ;)

Russ

Update. 1000 or so miles in France with some very hot days. Fan cuts in and out as required. Temperature gauge (for what it's worth) steady. Water level seems ok.