overheated the engine and now not starting

As an addition to above, battery now fully charged and cranking over beautifully. Engine firing regularly but not quite starting sort of like when no fuel.

I would be starting with a compression test, report the readings here for further assistance.

how do I do a compression test

You need a compression tester that screws into the spark plug threads, crank the engine over and it will give you a compression reading, just make sure that the leads are away from the tester as you don't want a spark jumping and giving you a boot....you may be able to hire a tester if you can't get one from a friend, make sure it is one with a flex hose as you don't have a lot of room to get in, also what model Commodore is it?

It is OK I just read that I need to get a compression guage, thanks

thanks for your guidance it is a 2000 VS ute 6 cyl with about 230,00km

OK, comp test will tell us a lot about what is going on in the engine, if you get a comp that is very low compared to the others, squirt a small amount of engine oil into that cyl about a table spoon full and re test the comp, if it comes well up there will be a ring problem if not a gasket or valve problem will be causing the low compression.

https://www.2carpros.com/articles/how-to-test-engine-compression

just bought a tester from super cheap. Do I just take out a plug and attach tester and then crank the engine and read the result

should i do all cylinders

have done all 6 cylinders readings follow
120
50 then with oil 65
3 others were 90
the last one i had terrible trouble getting unit attached which I think ieventually did
but reading appeared to be 0.

Sounds bad to me but then I really have no idea. What do you rthink

not good, 120 ok 3at 90 fair to poor 50 and with oil 65 will be valve problems or head gasket and 0 is a big worry try that one again and with some oil if nothing will probably be top end problems, but with the other poor readings, it will be a waste of time doing the heads as the bottom end is just about stuffed as well, may be time to look for a good second hand engine if you want to spend any money and keep the ute, trouble is a VS is worth not a lot these days and you have to weigh up the cost of re engine or scrap it, you will still be looking at 2-3k + to get a second hand engine fitted and do all the extras that will have to be done to ensure that nothing else goes wrong, may be worth getting a few quotes, where are you i may know some one you may be able to talk to first hand that you can trust.

I am in Highland Park, near Nerang on Gold Coast Queensland

Yeah those numbers are very bad. A normal engine will run about 135 psi and up and you want all of the cylinders within 10% of each other. So the range for yours, using the 120 cylinder as "good" you would want to see no lower than 108.

Hate to say it but I think you need a replacement engine or IF the block and heads test OK you might be able to rebuild that one. Overheating most modern engines is a killer, they don't have the amount of metal in them like the old engines, thinner castings and aluminum to save weight make them easy to hurt.

i will ask a few mate if they know anyone on the gold coast, i am down in Vic myself.

Thank you and happy new year you have made a bad situation bearable for me in which I have been able to see for myself what the actual problem is. 25 years ago I lived in Wodonga so just in Victoria

ok good luck with fixing the car.