UK Car Repair Questions? Ask a Mechanic for Answers ASAP
Id really doubt it would initially be a cracked block..as it will either leak coolant into the oil or cylinder"s" "stream vapour out the back tail pipe" or externally..but seeing as those 3 things arent apparent whilst doing checks would rule that out...have you inspected the expansion tank cap..if the seals gone it will allow coolant to escape in steam form..have you tried getting someone to do a coolant system pressure test..doing this would highlight any leak that only appears under engine hot conditions.it will also tell you if pressure is being lost when ..when the pressure is held on the system - there alos special uv dye kits out there you can add to the coolant and this using the uv torch/glasses provided with the kit to see if any uv dye is spotted leaking frm the engine or parts of the coolant system circuit..Its pretty hard to give an exact location of a leak as it could be on any number of areas on that coolant system..thats why you need to get the testing done to be able to narrow the areas on this...but seeing as you have done most of the basic checks..the next step is to get it pressure tested/or dye added to the system to help id the location..I do hope this helps
You must never mix coolant - if your putting a differnat brand/colour lets say..you need to drain/flush out the system first..then add the new coolant in... But i dont understand why you would just fill the coolant system with a coloured coolant. when your best oppertunity/advice now is to find someone else with the proper pressure test equipment to find out where exactly the leak is coming from...if that previous garage cant do it..then someone else might..