VZ is overheating - diagnostic?

[Ian555]

My VZ Commodore overheated in peak hour traffic, and even after cooling down overheated again (traffic flowing).

The first time it overheated the reservoir tank was dry. The second time it overheated, the reservoir tank had coolant in it.

After the engine cooled down the second time, I tried opening the radiator cap, turned on the engine and ran 3 litres of water in before I could see coolant appear in the hole. I opened the bleed valve on the radiator, but heard no hissing or any coolant coming out. I can't see any movement of water in the hole either.

What is the most likely problem?

 

[DeanoV6]

Probably leaking coolant from somewhere, Cracked radiator tank, water-pump, heater tap, thermostat housing at rear of motor, cast pipe from radiator hose to block, faulty radiator cap are all common, do a search for overheating plenty of posts about it. new radiator cap and pressure test is a good place to start

 

[Ian555]

I will look at it in daylight tomorrow, see what else I can find. Might get back on here after that.