Treat as urgent. If gas or CO is genuinely suspected, ventilate, get out, and don't operate switches or naked flames.
What it means
The base vehicle's engine is running hotter than it should. A fully-loaded motorhome climbing a long hill puts more strain on the cooling system than the same van empty.
What to do
- Pull over safely and switch the engine off as soon as you can.
- Let it cool before checking coolant level - never open a hot cap.
- Get it looked at before continuing; driving on can crack the head, a vastly more expensive repair.
Likely causes
- Low coolant level, sometimes from a slow leak
- A failing water pump or thermostat
- A radiator fan not engaging when it should
- Overworking the engine on a long climb, fully loaded
Rough UK cost
Coolant top-up is minimal; a water pump or radiator repair typically runs £250 - £700.