Forcing fan on to cool engine

[syncro_user]

My old (1989) VW has an after-run temperature sensor mounted near the inlet - if it detects high temps after shut-down (105C iirc), it triggers the radiator fan to draw fresh air into the engine bay, and cool the rad at the same time. Quite a simple system and easy to retro-fit. Controlled by a relay with a timer in it, and runs for a max of 10mins to avoid draining the battery. Thermosiphon effect will circulate the coolant to an extent. Could be worth a try?

[samwichse]

My HCH1 turns on the cooling fan when the engine is shut off for times between 1 minute and 5 minutes whenever it's particularly warm (I see IAT at maybe 50+C).

So there is some prior art on this.

Sam