I trying to figure out what wrong with the engine , I have to put collant every time I used my 78 monte carlo, i was looking for a leak or something but aint no leak , now is over heating , I replace thermosta but still over heating .

Any help will be helpful?

 

sounds like a blown head or intake gasket, pull out your dipstick if it looks like a milk shake you have a problem stop driving it's time to tear into it! , any smoke out the exhaust? do a compression check and see if any of the cylenders a really down on thier numbers

 

the oil look good is not mix with water yet, and yes sometimes white smoke come out the exhaust, compression is low

 

is it low across the board or just certian cyl

 

If you have white smoke, you have water leaking into cylinder, or making it's way into cylinder.

Make sure it's white smoke and not light blue. Light blue smoke is oil burning.