Car won’t start when cold

[badger64]

if you are losing your coolant and it is not leaking it can only be going one of 2 ways, into the sump via the oil or out the exhaust as steam, as you say the oil is black and no sign of a creamy header tank the engine must be burning it off as steam which you may not see until engine is under load ie when you are driving not on tick over. as has been suggested it looks like it could be your head gasket or cracked head as this would also lower your compression causing difficulty starting.