Do you have oil in the coolant, or vice versa? Likely, you've got a cracked head.
This is the byproduct of combustion. It's not problematic, and should not worried about, it's completely normal.
If the leakage is actually gear oil, this indicates worn seals, and or shafts'. Often times however, the leakage is not gear oil, but rather unburned fuel that has run down the exhaust housing, and leaked out of the gearcase. A pressure / vaccume check should confirm, or rule out, seal failure / worn shafts in gearcase.
theres a very good chance that the engine has a blown head gasket. what is happening is the water cooling the engine is escaping past the head gasket & into the engine, mixing with the oil making it milky coloured. the water is also escaping into the cylinders, making the steam come from your exhaust, you may also have trouble when turning the engine over, with water building up in the cylinders when cooling down.
Valve cover gasket
If it only occurs when the engine is cold or the weather is extremely cold, be suspicious of water vapor... it's a natural occurance during the combustion process. If the white vapor goes away when the engine warms up, no problem. If the smoke is blue-ish, it's probably engine oil. Check to see if you're getting fuel into the oil. That can cause the oil to thin and get past the rings, then the motor oil doesn't burn as cleanly and can leave the blue/grey smoke. That can be caused by dirty injectors that do not vaporize the fuel but sends it out in a stream, then the liquid fuel seeps past the rings to mix with the oil.
White, water vapor. Gray/black unburned gasoline. Blueish, burning oil.
This is the byproduct of combustion. It's not problematic, and should not worried about, it's completely normal.
If you're sure it's "smoke", then it's probably burning oil. But most likely it's water vapor. When an engine is first started and the air is cold, the water vapor in the exhaust will create visible steam. Automotible exhaust primarily consists of carbon dioxide and water vapor. If the engine and exhaust system are cold, the exhaust will be cooler when it comes out and it can create a cloud of water vapor. However, if it's not water vapor, as I mentioned above, it could be oil smoke. If that's the case you need an engine rebuild since you probably have bad rings. For the record, I haven't seen many newer GMC's that burn oil.
normally blue is worn rings,and black is unburned fuel.
It's carbon and unburned oil that you put in the gas mix. Using a gas mix with less oil will eliminate some of the unburned oil that comes out the exhaust but you need to be careful you do not run the engine with not enough oil in the gas as that is the oil that the engine needs for its lubrication.
engine burning oil( white or blueish exhaust smoke ), water in oil, oil in water, water in exhaust.
There is nothing to worry about with water in the exhaust. However water in your oil could suggest leaky gaskets. Depends where in the oil system or engine it is.
Usually a blown gasket, usually the head gasket. It creates a seal between the oil and the combustion chamber. When broken oil can leak in and you will have smokey exhaust and a dramatic drop in oil level, or exhaust gas (which includes H2O vapor) can mix with the oil. This is a very serious problem and can lead to severe engine damage.
If you are asking about contrails it is dependent on the temperatures aloft. At colder temperatures the water vapor in the exhaust condenses and causes the contrails you see. The blue angels and other aerobatic-performance aircraft inject a special oil "smoke oil" into their exhaust in order to leave the smoke trail you see at airshows. But the "smoke trail" you see behind civilian and commercial aircraft isn't smoke at all, it is water vapor formed as described above.
It's the same for all internal combustion engines. When gasoline burns inside the combustion chamber, it produces carbon dioxide and water vapor. The water vapor is usually hot enough that you don't see it, but when the weather is cold, and while the exhaust is still cold, some of the water vapor will condense together with other water vapor molecules, producing a visible mist that looks like white smoke out the tailpipe. It's normal. On the other hand, once the engine is warmed up, if the white smoke continues and if you notice that the engine is using a lot of oil, it may be that the rings and/or valve stem seals are leaking, allowing oil to enter the combustion chamber. When that happens you'll get some oil burning, which may look whitish-blue.
While an engine is cold, water vapor condenses and comes out the exhaust pipe as white vapor on a cold day. After the engine warms up, the exhaust pipe is hotter allowing the exhaust gasses to be hotter as they come out the tailpipe. When that occurs, the water vapor dissipates long before it can condense. Don't worry about it if it's just white vapor that goes away after the engine warms up. It's a normal product of the combustion of gasoline. On the other hand, if the smoke is grey and smells like oil, it can be an indicator of a problem. The oil smoke smell is in all probability the valve stem seals or the oil drain ports in the heads are stopping up.
It means that it has absolutely nothing to do with the oil and filter change. Backfiring is caused by unburned fuel/incomplete combustion/carbon buildup/incorrect ignition timing. The unburned fuel vapors pass into the hot exhaust and ignite just before the 1200 degree catalytic converter causing the backfire. However, ensure that you always check the oil level after having your oil changed by a third party.