That is where the old turbojets used to get their smoke from: Unburnt hydrocarbons. Can you believe the oil pressure on those 30,000hp machines is around 15 psi? Min for takeoff is 13 on the CFM-56 but nobody ever looks at oil pressure once its started.
Can't remember if I mentioned or not but big powerful jet engines run on 5w synthetic oil. The engines run half the cost of the entire airplane. You never change oil in a jet, you just add because the engine seals leak oil into the combustor section. They'll top off a motor with oil about every 30 hours or so. A 737 motor holds about 7 gallons of oil. Some engines burn more than others. Oil levels are measured and logged and the MX tracking computer sings out when a given motor starts to use oil faster than usual. Pilots have oil level gauges in the cockpit. Jet engines are run to failure. When specific metals start to show up in the oil indicating a bearing is going, the engine gets swapped (about an hour if they are in a hurry). Another reason for an engine change is an over temp in the turbine section, either during start or in operation. If the over-temp was slight, they will put the engine on a watch list and bore scope it periodically to make sure nothing is coming apart in the innards.
I flew a jet one night that had compressor stalled (loud repetitive BANG-ing or as quiet as a light "cough") on takeoff that day. MX tried to reproduce it and even flew the plane with no anomalies except higher than normal fuel flow. The Air Force didn't own a bore scope then and borrowed theirs from United MX in Oakland. That night we noticed the higher fuel flow but the engine put out what it should. The next day the bore scope revealed that 3/4 of the hot section blades were gone. One had failed in an upper stage and the cascading carnage took out most of his relatives downstream.
One more fun fact: Did you know the bearings in a jet are manufactured to such incredibly tight tolerances that their manufacture process is considered a state secret and is not disclosable to foreign entities?
Truly amazing machines...
BONUS! Here's an early commercial showing one smoking turbojet and the other not nearly as smoky. This was the first SWA commercial that used an actor instead of an employee. They had to shoot it three times because the girl fell down the first two times as as the plane flew over her. They got her to turn earlier and she didn't fall over. That hideous uniform was the infamous hotpants inflight uniform. A buddy of mine's sister worked back then and would go home on Friday night with bruises on her butt from getting pinched. Lots of cowboys got drinks dropped in their laps or got hit with serving trays. Ahhh... the old days. We have come a long way haven't we?
http://hotstewardess.com/category/southwest-airlines
