Some weeks ago I was driving my 84 Trans Am with LG4 engine on the highway. In past I lost some engine coolant. While driving I did not check that the coolant temp was getting too high. After some miles the "Check engine soon" lamp light up. I stopped the car immediately. Thank god the engine runs still. My problem is now that the engine coolant overheats after start even after 2-5 miles. I can't go anywhere with boiling coolant.
Which parts might I have to change first? Of course I have to fix the leakage. Thanks for your help guys!

 

You have to find the leak before you can fix anything.

Is coolant getting into the oil? Is coolant leaking onto the ground? Are you seeing white smoke out the tail pipes? Cooland doesn't just disappear, find out where it's going, then fix how it's getting there.

A compression/leak down test will see if you have a blown headgasket/warped head/maybe cracked block (haven't seen too many cases where it's that, though).

Pressure test the cooling system and pressure cap. Make sure the cap holds pressure. Start from there.

 

Thanks man for your quick answer.

The engine coolant leakage is outside the engine - coolant is leaking onto the ground. No big deal to fix it. Thank god no white smoke, no water in the engine oil.

The question is why it is getting hot so fast now ...

 

Is the coolant level topped off? The gauge can read extremely hot, really fast, if a large air pocket forms in the cooling system (happens easy if you lose enough coolant). Prevents the thermostat from opening while the lesser amount of coolant in the system boils away.

Where abouts is it leaking from? Front, rear, top bottom, side?