My car smokes when you first start it up but then it is ok once its warm we have had it looked at and they cant see the problem.?

Answer 1

I assume the smoke is coming out of the tailpipe. What color is the smoke?

If its a bluish color, which would be oil, then it sounds like worn valve seals. When the car is parked, small amounts of oil drip past the worn rubber seals, and into the combustion chamber. Overnight all these drips add up, so that when you first start the car, there is a bunch of oil that has to burn off, hence the smoke. Once that oil is burned off, the smoke clears. Even though its still dripping as you drive, the drips are so few and far between that you don't notice any smoke. This issue would cause your engine to use more oil than normal. Have you noticed that? Replacing the valve seals can often be down without removing the cylinder head. The mechanic removes the spark plugs, and attaches an air hose to keep the combustion chamber pressurized. Then they can safely remove the valve retainer without it dropping into the cylinder, and they can replace the seal, then put the retainer back on. They have to do this one cylinder at a time, moving the air hose, and turning the engine so that cylinders piston is at the top, with the valves closed, before they remove the retainers.

If it's a black color, then that is unburned fuel. If its an older car, with a carburetor, then it sounds like the choke is on too high or not releasing early enough. When an engine is cold, it requires a more concentrated amount of fuel to run properly. A choke accomplishes this by limiting the amount of air going into the engine. Less air, same amount of fuel, more concentrated mixture. The colder it is outside, the more choke that is initially needed. Once the engine warms up, and no longer needs the concentrated mix, the choke is supposed to release. If the choke doesn't release as soon as its supposed to, or if its on too high to begin with, then there is more fuel than needed, and black smoke. If it's a newer car, with fuel injection, then the concentrated fuel mixture is usually accomplished by the injectors just putting in more fuel than normal. A computer controls how much. If you had a bad engine temp sensor, that told the computer the engine is colder than it really is, the computer would add more fuel than is really needed, resulting in black smoke. It might still be adding more fuel than is needed once the engine is fully warmed up, but not so much that you notice any smoke. This issue would make your fuel mileage go down, have you noticed that?

If it's a white color, that is steam, which is your engine coolant burning off. That would mean engine coolant is getting into the combustion chamber. The most likely paths for that would be a blown head gasket or a cracked engine block, either of which is major $$. Is your engine coolant constantly getting low? Or is the coolant milky or foamy, or does the oil dipstick show milky or foamy stuff?