Engine overheating while temp gauge is normal, malfunction ECU due reverse battery connection

Question

A week ago my 2.4L 2009 sonata started transmission shifting problems and the mechanics told me replace the transmission fluid. The mechanics removed the battery and and started flushing transmission fluid by vacum pump. when the fluahing was finished, he tried to install the battery and connected it reverse for some seconds , when he realized his error and corrected the battery poles the car started with lots of lights (ABS, BAT, CHECK, AIRBAG), no ac, no radio. He told me its not a big problem and some fuses are broken and needs to replaced and asked me to get there tomorrow. When i get the car next day, every thing was ok, i have tested the car for 3 4 hours and everything was ok. Next day i was in the road for trip, everything was ok except increased fuel consumption displayed in instrument cluster. after 300km I heard some weird noises from engine, drived to the side road and engine stopped immediately . I get off from the car and see that large amount of white smoke comming from the engine (thats the engine oil burned).

I towed the car to another dealer, he said that your car was overheated, the crankshaft sensor was melt down and the oil leaked on top of manifold. He told me the only 3 liter of oil remained in my engine (1.5 burned) and it was totaly burned and black when flushed (replaced it days ago). I was suprized to hear that, because the temp gauge was normal.

So i wounder that reverse connection of battery caused the ECU to malfunction. When i relalized that my engine is blowing and its overheated the temp gauge showed normal temperature as earilier. Is there any condition that the engine is over heated but its not indicated by temp gauge? is temp gauge related to engine body temperature or coolant temperature? when the coolant leaked and the car is low on engine coolant, is it possibile to temp gauge doesnt show the correct temperature?

Also i found that there is an electrical leakage in car, the battery drained when i towed car and next day the mechanic started the engine with another battery.

Answer 1

Ok, so for most modern cars, connecting the battery in reverse is a BIG problem. Nearly everything electronic can be damaged or destroyed in just milli seconds.

A clown mechanic jumped started my mother's car once with the cables on backward and it ended up costing $1800 to fix everything that was wrong. Plus some damage may not be immediately evident.

DO NOT use this mechanic again, he's clearly careless or incompetent. Take the car to a qualified mechanic and let them find all the damaged components. Yes, it may take some time but you have few other choices.