white smoke out tail pipe on 1994 Mercedes-Benz S420

it smoke when in park or stop at a light

Asked by for the 1994 Mercedes-Benz S420
The most accurate way to test for a blown head gasket on a gasoline engine is to test for the presence of carbon monoxide in the cooling system. Snap-On, Matco (part # CO 2000), and Napa sell a tool to check to carry out this test. Another link to a supplier of this tool is Carbon Monoxide is only present if there is a blown head gasket or cracked cylinder head. I think the napa part number 700-1006. . Signs of a blown head gasket are coolant loss (frequently have to top up the coolant level of the engine without seeing an obvious leak), experiencing over heating or rough engine running or the presence of white sweet smelling steam from the exhaust. A badly blown head gasket may allow engine coolant and oil to mix.
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This is normally an indicator that water is burning in the engine, and is most often from a blown head gasket. Here is some info:
I also had white blueish smoke, my problem was the o2 sensor went out