The D4 light only comes on when the car is Way overheating.. I discovered that today, then shortly after the Check engine light will come on...


I started changing the antifreeze today... And while i was going through the motions of cleaning it out... I noticed all the smoking that is happening in the engine is coming from the Backup coolant reservior.... Like it will start to hiss and leak and them smoke????
Whats going on?
I brought a new thermostat Just in case.. i have yet to install it