M54 engine viscous fan. Not sure if I have an issue.

[Pond]

Bear in mind that a car sat ticking over will never heat up as much as when it's being driven, so any amount of sitting running for 90 mins won't bring out any problems.

I know but with something like this there is no other way to test it (that I know). I can't drive down the road sitting on the engine and keeping an eye on it! For a start I would burn my bum.