Red temp light came on and temp needle was up at 120 and went into limp mode. Then after 6-8 seconds needle dropped quickly to where it should be and van came alive again. Checked coolant seemed low, topped it up now aggressively overflowed. Please help. Transit 350 ecoblue 21 plate.

There was an airlock in the system. It might have bled itself now.

Coolant will overflow if you remove the cap when the engine's hot. The pressure from the cap maintains the level.

14 hours ago, James maclean said:

Red temp light came on and temp needle was up at 120 and went into limp mode. Then after 6-8 seconds needle dropped quickly to where it should be and van came alive again. Checked coolant seemed low, topped it up now aggressively overflowed. Please help. Transit 350 ecoblue 21 plate.

Could be as Tom mentioned. But it can also be that if the coolant was too low it's not allowed the oil in the cooler to be cooled down enough which causes limp mode too as soon as it cools it acts as if it didn't happen. This could men that you might have a small leak in a pipe and you should have it checked if the coolant runs low again.