Suspect engine seized

hi , i have a discovery 300tdi last year had head gasket replaced by a trusted garage last month had timing belt waterpump done , then radiator was leaking and noticed engine overheated got new radiator and thermostat and it ran ok for 3 weeks driving a lot of miles too . Then on the motorway doing around 70mph noticed a quiet knocking and sudden loss off power quickly followed by engine cut out , and a bit of smoke under bonnet due to a slight oil and dieselleak on rocker cover, got home noticed no water in header tank no obvious leak , tried turning crank but won't budge . If engine is seized what could have caused this

Oil and diesel was leaking from there

When my head gasket went all the water went in one of the pistons and caused hydraulicing

backinblack said:

When my head gasket went all the water went in one of the pistons and caused hydraulicing

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I'm

backinblack said:

When my head gasket went all the water went in one of the pistons and caused hydraulicing

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I'm guessing if it's head or head gasket gone on mine it would have been due to overheating a few weeks ago? I would have thought it would have happened when engine hot and not after it had overheated

Mine had a pitted head so started with losing water intermittently. Have you dropped the oil out of the engine to see if it's mixed with several litres of water?

Just checking the oil level should show increase if full of water.
Take glow plugs out and try turning engine over.

Blackburn said:

Just checking the oil level should show increase if full of water.
Take glow plugs out and try turning engine over.

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Just checked dip stick it's over full mark but not a lot , a mate of mine took out a couple of plugs and tried to turn it over , nothing happened it just sounded same as wen plugs were in

alan1974disco said:

Just checked dip stick it's over full mark but not a lot , a mate of mine took out a couple of plugs and tried to turn it over , nothing happened it just sounded same as wen plugs were in

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You need to take them all out as one cylinder may be full of water.

How much coolant is in? Any coolant leaks at the front of the engine block around the alternator?