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Hot and Cold Radiator


My rad get s hot at the top, but stays cold at the bottom. There is a new stat in it so I was wondering if the rad was knackered. Temp guage climbs to red and stays there.
Never tried it, but I am told that a solution of caustic soda is good for flushing rads. Can anyone confirm or otherwise?
Well, rad flushed in both directions, water is as clear as a mountain stream, no rust came out or other crud. Water pump is fine, as is the heater matrix as is the thermostat. But the needle is still in the red and the bottom hose is cold:confused: :confused: :confused:
Are you sure the thermostat is working, sounds as if it is not, give it a try with the thermostat removed, may take longer to warm up but will prove or disprove. Better than have a cylinder head gasket go.
Could someone explain the flow of water round the engine for me so that I can get this in my mind's eye? As I understand it, the stat must be opening to allow water into the top of the radiator, or am I wrong? Thanks for the help thus far.
Your right water comes up from the bottom rad hose throught the pump to the block and head then past the thermostat to the top hose and into the top of the rad when the thermostat is closed the coolant goes down the bypass hose back to the pump. I warm up the engine with the rad cap off, when it gets up to temp look through the rad filler and rev the engine slightly to see if coolant is flowing from the top hose it gives me an idea if everything is flowing correctly.
If the thermostat only opens partially, it would give the symptoms you describe. replace it with a new one and see how you get on.
I would go with Nick. If the wax has partially gone, the stat won't open properly and will leak a bit of hot water past. If the stat has failed and is closed, you get a hot bottom hose and a hot rad bottom.

If it's like a K Series, Ford Cologne V6, etc, and has the stat in the bottom hose, the top hose gets hot and the top of the rad, heat transfer through the water and usually a lot of banging in the system.

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