There are two hoses that typically fail on the 1.7, both located close to each other below the thermostat housing, small 45° hoses.

The third one that can be a problem is the small 90° elbow going to the oil cooler on the back of the engine.

 

This shows the front ones.

[Meriva A] [02-09] - 1.7 CDTI Water Leak

Came back home on Sunday at about 10pm when it was relatively cool and heard the radiator fan spinning down when I shut the engine off. The fan almost never comes on normally so made a mental note to check the water level the next morning when the weather was better. Next day found the header...

www.vauxhallownersnetwork.co.uk

 

I top up the radiator with water and I don't see any leak coming from the hoses, no leak under the car, but at high temperatures the coolant escapes from the expansion tank valve.
I used to replace those hoses several times, but they seem to fail pretty easily.

 

The Astra H does have a temperature indicator it's in the hidden menu on the radio (assuming you have the standard CD30).
With the engine running and radio turned on, if you have the two line radio display (with two buttons under the screen) you get to it by holding the settings button on the radio for about 10 seconds (until the radio beeps), then pressing the right hand button 16 times. The display lower line then shows the vehicle speed on the left (in km/hour), and the engine temperature on the right.
If you have the three line display, again hold the settings button till the beep, then press the button below the settings one on the radio (I think it's marked B/C) again 16 times I think.
There are information screens for each press of the button, but the only other one that is useful is after 12 presses you get the battery voltage.
If you turn the engine off & remove the key the display reverts to normal. Any long journey, especially when towing, I always get the temperature up on the display.

 

Yes I know this trick, but every time you turn on the car you have to do this, and sometimes you just forget. Stupid Vauxhall/Opel engineers who decided not to have a temperature gauge on the dashboard.

 

The most common hose to fail is the long by pass thermostat hose , it just splits open pouring coolant out all over the road. Another common hose failure is the top hose going into the heater matrix , it will develop a pin hole & when the engine is given some throttle the coolant sprays out all over the engine bay causing a right old mess.

 

I am really sick with the cooling system of my car, it seems to fail very often.
A repair shop said that replacing the head gasket and some other components would cost me about 330£ including labor.
Another one offered a new used engine for 370£ including labor.

Which option might be best?