White Smoke or Steam from the Exhaust Pipe
White smoke or steam is a natural by-product of the engine combustion process. As the engine and exhaust system heats up the steam is completely dissipated before it exits the exhaust system, becoming undetectable. The amount of steam produced from the tail pipe while the engine is cold varies due to outside temperature and humidity. Although if a massive amount of white smoke or stream is present even long after the engine has been warmed up this could mean you have a problem.
Coolant/antifreeze is used to cool the engine during normal operation. If coolant is allowed to enter the combustion chamber, the engine will burn the coolant creating white smoke and steam. When this white smoke/steam is being produced it will be accompanied by a sweet, pungent odor. This will be accompanied by engine coolant loss with no visible leaks. There are four reasons engine coolant will enter the combustion chamber.
Car Repair Guide
Step 1 - Inspection - The engine intake manifold is used to direct air and fuel into the cylinder head combustion chamber. Most intake manifolds utilize engine coolant to help cool and distribute coolant into the cylinder head (s) and then down into the engine block. If the gasket that seals the intake manifold to the cylinder head fails it can allow coolant to enter the intake port and then the combustion chamber. To check for this condition the intake manifold will need to be removed. Once the intake manifold has been removed inspect the gasket. If the gasket has rotted or dilapidated between the intake port and the cylinder head it could allow coolant to transfer into the cylinder head. Replace the gasket with a new unit and reassemble. If the intake gasket is ok continue to the next step.
Step 2 - Inspection - Anytime you have coolant in the combustion chamber and the intake gasket is ok, the engine must be disassembled to locate the failure. These options are not so pretty. There are three remaining causes for coolant to enter the combustion chamber and all require engine dis-assembly. This can be tricky because the repairs overlap and it is difficult to tell which one is causing the problem before dis-assembly. For example: A repair shop has told you the cylinder head is cracked, and as they start dis-assembly they can discover it was the intake manifold gasket that has failed. It's up to the honesty of the repair shop to alert the customer the repair will be less.
Or the opposite can happen, example: A repair shop has told your engine has a blown head gasket, once the dis-assembly is complete they inform you the head gasket is ok, and the cylinder has been pressure checked and is ok. This only leaves the engine block as the failure and must be replaced to repair the problem, and that can be costly. If the head gasket has failed, be sure to have the head pressure tested to be sure it is "okay" internally and surfaced to be sure it is flat so as to mate evenly with the engine block.