General Grey smoke out of exhaust?
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General Grey smoke out of exhaust?
Grey smoke typically indicates that the car is burning oil. Undoubtedly is rarer than the types you listed however becomes common on higher mileage vehicles.
43576
Member
Thanks.
This is a diesel isn't it? Does it do it at all engine temperatures? Cold diesels can produce greyish smoke especially when cold, due to incomplete combustion. If it largely goes away when hot I'd not worry about it - specially if she doesn't seem to be loosing coolant or using oil.
43576
Member
Yes it's diesel, when is mild warm till about 3,000rpm or less, but nothing when the engine is fully warm. That's great nothing to worry for now.
Older diesels tend to be prone to doing this especially once a bit of wear is present which might mean there's less compression. Modern diesels tend to keep the glow plugs "lit" for quite a while after start up which, amongst other "benefits", reduces Diesel knock and this smoke problem.
Here's some quite entertaining and extreme video of diesels cold starting:
Notice how many of them make white smoke due to incomplete combustion because the inside surfaces of the engine - cylinder walls, combustion chamber, etc are cold and the fuel, so precisely vapourised, by the injector condenses out on them into a liquid and the liquid fuel will not burn so readily as the vapour. Notice too the black smoke which is due to the injector pump overfueling (injecting too much fuel for the air being admitted) This happens because the system detects that demands are being made to increase revs even though the revs aren't actually increasing so it just starts to over inject. Diesels, pretty much - there are a few exceptions - completely fill their cylinders with air on every intake stroke and regulate revs/power by altering how much fuel is injected into that air. If the revs don't rise it just keeps on injecting more fuel so you get black smoke! The reverse is also true in that often if a vehicle is making black smoke on acceleration you'll find it's got a clogged air filter stopping enough air getting in! (Often an indication that the vehicle has been poorly maintained)
One of the garages I worked in when I was young was located in a large old building where the boss made extra money by allowing local companies to park their lorries and vans inside overnight for security. Of course this meant that every morning the first thing we had to do was start them all up and drive them out into the yard so the place could function as a workshop. The smoke from, sometimes as many as 20 vehicles, was absolutely choking and I can remember times when my eyes were streaming with tears so much I couldn't see! In the summer it wasn't too bad but sometimes in the winter the fumes would linger for the first hour or so of working and it really wasn't very nice. The health and safety people of today would have been horrified!
PS. Looking at the video lets you realize why diesels nearly always have pretty big batteries!
Notice how many of them make white smoke due to incomplete combustion because the inside surfaces of the engine - cylinder walls, combustion chamber, etc are cold and the fuel, so precisely vapourised, by the injector condenses out on them into a liquid and the liquid fuel will not burn so readily as the vapour. Notice too the black smoke which is due to the injector pump overfueling (injecting too much fuel for the air being admitted) This happens because the system detects that demands are being made to increase revs even though the revs aren't actually increasing so it just starts to over inject. Diesels, pretty much - there are a few exceptions - completely fill their cylinders with air on every intake stroke and regulate revs/power by altering how much fuel is injected into that air. If the revs don't rise it just keeps on injecting more fuel so you get black smoke! The reverse is also true in that often if a vehicle is making black smoke on acceleration you'll find it's got a clogged air filter stopping enough air getting in! (Often an indication that the vehicle has been poorly maintained)
One of the garages I worked in when I was young was located in a large old building where the boss made extra money by allowing local companies to park their lorries and vans inside overnight for security. Of course this meant that every morning the first thing we had to do was start them all up and drive them out into the yard so the place could function as a workshop. The smoke from, sometimes as many as 20 vehicles, was absolutely choking and I can remember times when my eyes were streaming with tears so much I couldn't see! In the summer it wasn't too bad but sometimes in the winter the fumes would linger for the first hour or so of working and it really wasn't very nice. The health and safety people of today would have been horrified!
PS. Looking at the video lets you realize why diesels nearly always have pretty big batteries!
