What could cause a car to run sluggish then make knocking noises have white smoke from the engine then die and not start again?

Check your oil,- is it foamy?

Examine your coolant. Does it smell like oil?

Is the smoke sweet smelling?

Knocking has nothing to do with a head gasket, sounds like you have multiple engine issues to me.

And finally...if changing a head gasket is simple, why does it cost so much? because if you don't work on cars all the time it is most definitely not simple and includes timing belt removal usually.

Overheating can cause knocking. then refer to the above....

Your best bet is to replace your motor because usually the knocking noise is caused by a spun bearing which would cost a lot to repair.

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The white smoke is from a blown headgasket, your coolant is leaking into one or more cylinders and that's actually steam that you see coming from your tailpipe.

When this happens, your coolant level drops (because it's pumping it out the tailpipe), your car overheats, and of course it will knock as it overheats. An overheated car is sluggish, as well.

Another bad thing that occurs by driving a car with this problem is that the coolant is washing the oil off your cylinder walls and your rings will tear up your cylinder walls as they self-destruct.

Head gasket replacement is not an easy fix nor is it cheap, and usually you'll need to get the head machined to make it perfectly straight again - heads warp from overheating. A good mechanic can do a head gasket replacement in a few hours.

- Dazani

This soudns like engine failure. Probably blew head gasket and ruined the engine due to it being run with bad head gasket too long.

You can find a god used engine with lower miles for around 800 at the most. usually more around 500 or 600 at most yards if you call around.

Labor to replace an engine we charge about 300 to 400 usually.

The car may not be worth doing this with however, some are not.

Most are though, if clean straight and drove fine.

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If your vehicle has a Diesel engine, then you may just be looking at 'fuel starvation'! All of the above are to a degree correct - but unlike Petrol engines, Diesel engines are also known to emit white smoke through the exhaust system when fuel delivery to the cylinders is restricted and give off the same appearance as a head-gasket problem.

This could also cause 'sluggishness' or lack of power, bad starting or non-starting and also a low type knocking noise.

Change the filter and check that the fuel lines are not clogged or restricted; you could even possibly run your own fuel supply line from a can to check this part out if it's easier for you!

Start the engine and rev it at about 3,000 rpm for a few minutes or take it for a short drive to see if it still loses power, if it still does then assuming all has been changed and cleaned, you might look to see if there is something in the fuel tank that could be blocking the supply pipe!