Hello Mandy here. I have a 2013 Chevy Sonic. Saw a puff of steam from under the hood and have a oil in my water. Check engine light comes on. Did a block test with fluid in perkulator on radiator cap. Passed that test with no exhaust fumes in radiator. Could not maintain pressure in cooling system to test if water came out Pistons under spark plugs. How do I know if it is oil cooling gasket or water pump?