Why is white smoke coming out the tailpipe only when I stop at a red light or traffic for more than 6-7 minutes?

Answer 1

White smoke from the exhaust is a symptom of coolant entering the combustion chamber. This is almost always caused by a blown head gasket or cracked head, or both. This will cause severe internal engine damage if not repaired. STOP driving this vehicle and have this repaired immediately.

I'd like to add that making the statement that smoke from the exhaust in today's modern diesel engines is not always a symptom of a cracked head or failed head gaskets. I noticed f-350 in the category area below the question and if the question is in reference to the Ford 6.0L diesel white smoke from the tail pipe 9 out of 10 times is caused by a blown EGR cooler. The cause of the failed cooler has been linked to the oil cooler element coolant passages being plugged from lack of maintenance, abuse, and just a bad design. The coolant enters the oil cooler first and exits directly into the EGR cooler so if the oil cooler is restricted and the full flow of coolant is not entering the EGR cooler at a fast enough rate the hot exhaust gases that are also in the EGR cooler fracture at the welds internally and cause coolant to enter the intake manifold. By design the EGR cooler cools exhaust gases which are re-introduced into the intake. Now that the cooler is fractured coolant along with the exhaust gasses are entering the intake to be burned. When this happens the engine produces a very thick dense white smoke. This is very common on the Ford 6.0L and blown head gaskets or cracked heads are incorrectly thought when people see the white smoke.

Another example from many of white smoke that has nothing to do with blown head gaskets or cracked head(s) is on medium diesel trucks Isuzu, Hino, UD Nissan, Cummins, and Mistubishi to name a few. When the EGR coolers fracture on these it's the same white smoke as the 6.0L it's just not as common. It happens occasionally. The other failure is when one or more fuel injectors deliver too much fuel to the cylinder and the engine can't burn all the fuel that is being dumped into the cylinder and white smoke the complaint. The fuel injectors are constantly correcting how much fuel is being delivered to the engine. Their are many, many factors the ECU takes into consideration to calculate this value. It even gets so complex that the japanese don't even try and explain how it's calculated. For years they didn't even have a spec for them. It's main purpose is to keep the engine's idle/running as smooth as possiable. This value is called the fuel injector(s) correction value. Ideally you want 0mm cubed. Every model is different but for lets say the Isuzu NPR if values are above 4.5mm cubed the injector should be replaced regardless. When the values get to 8-20mm this is when you start getting the white smoke and customers saying "I think my head gasket is blown." No it's your injectors thats causing the smoke. This is for diesel and in my opinion the first answer is completley correct for gasoline engines. Modern diesels have alot of different emission components added on to them these days and diagnosing can be tricky because of them.