It may seem cold at the moment, but now is a good time to start preparing our cars for the coming months of increasing temperatures. The cooling system is a good place to start.
The poor ol’ radiator cap is often forgotten and sometimes considered just a simple part of the cooling system. But it’s not that simple and does a lot of work.
If one of your engine cooling hoses seems ‘squashed’ or flattened when the engine is cold, check the small centre valve on the underside of the radiator cap. This is the low pressure valve which allows air into the radiator as the water cools and contracts. It should be easily pulled down against its spring pressure with your finger and snap back. If all okay here, the hose in question is likely to be faulty and its structure breaking down.
Check the main rubber seal. It should be free from cracks and be flexible. The seal together with the main spring keeps the system pressurised. Any faults here and you will lose water and overheat. Also check the upper seal, which prevents water escaping past the radiator filler neck, particularly important if an expansion bottle is fitted. Remember, only remove the radiator cap when the engine is cold
Any doubts…fit new a new cap!
Next time: coolants and air locks.