406 2.1 (1998) diesel cooling fans

[PiMuRho]

Bear in mind that I bought the car in December, I've realised that I've never ever noticed the radiator fans coming on.
The car runs fine in air, it barely touches 80C on the motorway. However, it does start to creep up to 100 in slow-moving traffic. Obviously, with the weather here now approaching summer warmth, I'm concerned about the car's ability to cool itself. I've had a pre-emptive look at the relays (they seem fine visually) and the fans themselves (same) but what else can I do here? What else is in the chain that I can check/replace?

[steve_earwig]

If you pull the brown connector off the sensor on the thermostat housing the fans should both run full tilt. If they do then replace the sensor, if not then things get tricky. I guess what you could do is provide 12 volts to the relay output terminals, although I can't actually remember which is which

[Rolebama]

FWIW, on mine, when trying to diagnose a non-start issue. Under the battery, there are two brown multiplugs. When disconnecting the one nearest the engine, the fans ran in 'slow' mode for a couple of seconds, before running full tilt. I don't know if this will be helpful or not!?