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Old 21-12-07
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9008v 9008v is offline
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Default white smoke

I am restoring a 1985 saab 900 8 valve car. I started the engine a few weeks ago, and I am getting severe white smoke. If I put my hand in the smoke it will be dripping wet within a few seconds! I have carefully marked the water level in the tank and it does not drop, so where is the water and smoke coming from? Here are my thoughts, and any additional info you can add would be greatly appreciated! This is the first engine I have rebuilt so I have very little experience.

In my opinion white 'smoke' is actually water droplets, simular to steam out of a kettle or your breath on a cool morning. Wheither you see it or not depends on
A) The ammount of water in the air
B) The temperature of the air
The hotter the air is, the more non-visible moisture it can hold. If there is more water than it can hold in moisture, then visible water droplets are formed!

When you start the car the exhaust pipes are cold, and the hot exhaust gasses get cooled. As they cool, the non-visible moisture forms visible water droplets. The droplets can be formed before the gas comes out of the tail pipe! After the pipes warm up, the gas doesn't get cooled as much and is clear in colour as it leaves the tail pipe. But it is still a race against time! If the cold air outside the car cools the gas quick enough, water droplets will form before the gas mixes with the air.... and that is how the white smoke is formed.

So, white smoke at startup, can indicate that there is more water in the gas than usual. Just because the steam disappears after the car warms up doesn't mean that the extra water is also gone. It just mightn't be visible!

Combustion of petrol produces water. This is where the water on my hand came from. (I hope)

If the air to fuel ratio is incorrect, the combustion temperature and the ammount of combustion water produced will be effected, which both can produce white smoke.

Contanimants can also effect the combustion temperature and water. For example oil. Oil burns with a black colour, as is obvious when there is a large oil leak into the cylinder. But, in smaller quantities it can result in bad combustion and white smoke. As the quantity increases, the white steam mixes with the black smoke to produce 'blue smoke'! (I don't know all of this for certain, it is just my opinion!)

So, that's the tecnical side! ...

Another site said that it could be caused by too high an oil level. As the crankshaft plunges into the oil it can splash extra oil onto the cylinder walls. Also, the plunging would airate the oil. The oil pump would suck up air bubbles and less oil, which can cause engine damage!

Something as simple as a blocked air or fuel filter could cause it! Also any air or oil leaks in hoses. The list is endless! White smoke could be just an indicator of bad combustion, without burning anything extra!

Although, if there are plooms of smoke, this is most probably the head gasket. Smell the smoke. If it smells sweet that is antifreese burning.

Which leads me to head gaskets. Most of the water channels going from the block to the head are blocked off on purpose by the head gasket. The holes that are present are of smaller diameter in the gasket than those on the metalwork. If corrosion widens these holes, or blows through some of the blanking off gasket, the engine can warm up noticibly quicker, the fan come in very frequently in heavy traffic, or even cause the engine to overheat.

Ok, i'm starting to ramble now!

Can anyone suggest the most likely problem with my engine based on past experience with a 1985, b201, non-turbo, single carb, 8 valve engine?

Michael
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Old 21-12-07
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More often then not, and especially with the 8 valves, if the engine has sat for a long time it takes at least a full tank of new fuel and some brisk driving to eliminate built up condensation in the exhaust etc and whatever may have become of the old fuel in the tank. If you're not losing coolant, if compression is good and equal across all 4 cylinders, if the oil looks clean, then you probably have nothing to worry about.
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Old 21-12-07
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Thanks for your reply. I cleaned the tank and the engine was started shortly after rebuilding. The exhaust stytem might be the culprit. I haven't had it on the road yet, so i will wait to see what happens.


I am getting 11.75, 11.75, 12, 11.75 bar compression, after maybe 1 to 2 hours idling and driving in 1st gear. What is the normal pressure for this engine? Can it be calculated from the compression ratio?
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Old 21-12-07
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converting that to psi, thats 175-180 psi per cylinder, which I think is about right for an 8v NA. No worries there.
You are not losing coolant, so the smoke has to be water vapour from the petrol, as you have surmised. Don't worry, and just enjoy driving the car!
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Old 30-12-07
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Thanks. Its good to know its about right. Do you have the exact figure it should be? Its a b201 engine if that would be any indication.
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