ANNOYING COOLANT LEAK
I own a 1984 Vauxhall Nova 1.4L. The problem I have is coolant loss from the top hose where it connects to the thermostat housing at the timing belt end of the engine. This leaks coolant from both ends of the hose.
I’ve fitted a new hose and a new coolant pressure cap, but without success. I’ve also carried out a compression test on the engine and all cylinders registered around 13.5 – 14 bar. If the expansion cap is removed after the car has been used no coolant leaks from the hose.
The system is pressurised, as a distinct hiss appears when the cap is removed. I suspect that the head gasket may be leaking gasses into the cooling system causing excessive pressure, which is causing the hose to leak. But as the compression test proved satisfactory I’m unsure. Simon Kite I don’t believe that your head gasket has blown, as if this was the case removing the pressure cap after running would be likely to produce far more than a hiss. In fact, it would produce a much higher pressure that may also push out hot coolant. This is one of the reasons that the pressure cap should always be removed with caution after the vehicle has been running. The pressure cap should also open to release excess pressure before it leaks through any other component of the cooling system.
It should be noted that even with good compressions, the head gasket could still be leaking gasses into the cooling system. Another check you can make is to run the engine at around 2000rpm with the expansion cap off. If the head gasket has failed, you should see small bubbles coming to the surface of the coolant. There are also kits available to detect for any C0 gasses in the coolant. This method is good indicator of the head gasket integrity.
If there are no head gasket problems the most likely cause of the weeping coolant is corrosion to the thermostat housing outlet. This often causes the outside face of the outlet to become so uneven that a good seal cannot be made. Removing the hose and ensuring that the mating surface is good should rectify the problem.