I've BMW 318i E90 2007 which is heating up after about 2-3 miles and since it has been heating so quick esp in down town and low speeds, I have not had a chance to take it to highways. Now, there are many things which have been done (potentially wrong) to this car.
Mix brand coolant & water with no regard to ratio of water and coolant. Basically a ignorant mistake!.
KSeal coolant was added as a percussion to stop any leaks if any.
The Engine was re-built some time back by some local whose work I don't believe at all. And now I also suspect that the HG has blown as there is some knocking sound from day 1 after engine rebuilt.
Sometime back (After the engine rebuilt), a pressure test on coolant was A OK. but there are definitely coolant leak marks on the ground.
I am now baffled with what to do and what not to. Here is what I've come up with in the order to get this fixed.
Check radiator (Cooling system) for blockage and pressure test properly for long time.
Coolant drain (with vacuum) and flush the system 2-3 times and pressure check again.
Fill the system (Vacuum filling) with BMW coolant only with proper bleeding.
If these 3 steps don't work, change the Thermostat which might have gone bad after wrong coolant etc.
If change of Coolant thermostat does not work, then the Head Gasket.
I would highly appreciate if someone please help me and share their thoughts on my approach.