smoking 1985 300 turbo diesel

Just a basic question. The ad for the car reads:
"give her a little gas when starting in the upcoming cold days, for a smooth start (diesels like warm weather), firm, solid shifts through
all gears and smokes very minimally (this is a diesel trait)."
What should I know about smoking exaust. Also, what is "blow by". Other ads for simular 80-85 300 TD 's assure that thier car doesnt "smoke".... So in a nutshell what is this "smoke" and what is it a sign of, what is blowby and how do I test for it? any advice would be helpful!!!
Mike
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Smoke is unburned fuel. So why is the fuel not burning as it should. Could be as simple as a dirty air filter or as expensive as the low compression of a worn engine. That said, most of these old diesels will smoke upon hard acceleration because they always have. Low sulfur fuel cuts the smoke and low sulfur fuel is being distributed more widely as time passes.
A diesel is a compression engine, that means the engine's 21:1 compression ratio sufficiently heats the air inside the cylinder to ignite the fuel at the moment of its injection. Worn engines no longer have 319-348 psi of compression, they're down around 220-240 psi - below that they won't start. You begin to see the equation: compression makes heat and heat ignites the fuel. Now lower the ambient temperature to 10 degrees F. and the marginal engines don't start.
Blowby is simply the lost compression - every engine, gas or diesel, has some blowby, there's no measurement of blowby so forget blowby.
If you want to buy one of these diesels have an independent M-B shop do a compression test for that's the ONLY way you will know the internal condition of a diesel engine. It will cost you $100 or $150 and is $$ well spent and without regret to KNOW the car you're buying is reasonable or to avoid some run out dog that needs an overhaul before the cold weather hits.
A reasonably maintained 617 M-B diesel should be good for 250K to 300K miles, longer if very well maintained. So if the car looks great and the owner has complete maintenance records that show engine oil and filter changes every 5K miles it's probably a good car, otherwise be a skeptic.
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Thank you TG for that great response, very informative! KH

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