I have a Honda Civic 2006 lx with1.8 lit engine and millage is 243000KM.
What could cause gray sludge to end up in my coolant overflow and on radiator cap.I think stuck on cap when pass from radiator to tank. I cleaned tank and check a every 2 month almost 1 or 2 inches collects. Thank you
It is possible that along the way someone has put some additive in the cooling system. If you are unsure you may want to flush the radiator.
You can flush the system and then test it to see if it returns or not. If the sludge is not from an additive then it is a good thing you have found it. Now you just have to flush out the system to get rid of the gray sludge. Purchase a radiator flush kit and liquid flush from you local auto parts store. I will provide links below as well for online purchase. The Flush kit should come with instructions to follow on how to install it. Just make sure the engine has had a chance to cool down before installing the kit. After you have installed the kit, put the liquid flush in and drive around with the heater on. This will insure that the flush gets into all the different water jackets and heater core. Follow the instructions and flush. Be sure to drain the radiator from the radiator drain plug. Use new coolant to refill when done.