Something a bit worrying happened today. Took it down the motorway, got 20 mile or so and the temp gauge suddenly shot up. Slowed down and pulled off, steam coming out of the bonnet, and coolant flooding down the road from underneath. Looks like the expansion tank had been overflowing, water everywhere around it. Took the rad cap of slowly, loads of pressure in there, and coolant level in there is low and very foamy.
Filled it with water, and carried on, absolutely fine the rest of the 60 mile journey. Went to check the level before returning home and it had maybe lost a little 200ml perhaps but again foamy. Drove 60miles home and the temp stayed normal even when given some.
I know these are prone to HG fail, and foamy coolant a sign, but anything else could cause this that i should try?
Cheers
Phil