Tip & How-To about Cars & Trucks

Blue Smoke from Tailpipe

Blue smoke from your exhaust (tailpipe) is caused by engine oil finding its way into the combustion chamber where it is burnt alongside the fuel.

The 2 main causes are:

  • Worn valve stem seals/worn valve guides
  • Worn pistons/rings .. a worn engine.
And also a combination of both the above.
Valve Stem Seals/ Valve Guides
valve stem seals and guides Google Search

A valve stem seal is simply a rubberised seal that fits onto the valve stem. It prevents oil from the rocker box from trickling down the valve stem, and into the cylinder bore.

If the stem seals perish or split, oil can find its way down past the valve and into the combustion chamber. This is most noticeable at start-up when a cloud of blue smoke appears behind the car. The amount of oil lost is actually negligible. It only takes a couple of drops of oil to create that blue start-up cloud, which soon clears.

The valve guides are what the valves move up and down in. With age/wear (or infrequent oil changes..) the bore of the guide becomes slightly oval. This allows the valve to have side-to-side movement and oil can find its way into the combustion chamber.
There's different oil additives that you can try
valve seal additive Google Search

If an additive doesn't work, Cylinder head removal is required to replace valve stem seals/worn valve guides.

Worn Pistons/Rings
Worn engine ...
worn piston rings Google Search
Worn piston rings/worn bore allow engine oil up from the crankcase and into the combustion chamber, where it is burnt. There may be a constant faint stream of blue smoke as you drive, particularly noticeable when you accelerate. Your oil level will probably drop noticeably and there may be a 'burnt oil' smell when you get out of the car.

Fitting new piston rings can be a pointless exercise. Where the ring fits into the piston groove - that groove can become 'rounded' because of the flexing of the ring on the piston up and down movement. Fitting new rings onto worn pistons is pointless. You must replace the piston as well.

If the bore is worn - ovalled - because of the wear on the cylinder walls caused by the up and down piston movement which causes the wear, fitting new pistons is also pointless. The engine should be rebored. That entails new big end bearings and a cylinder head overhaul. On an older car it's often cheaper and easier to replace the engine with a second hand unit.

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2 Answers

Finding oil on ground by left tailpipe. Any suggestions of what could be happening and how to fix it?

Engine oil is entering the combustion chamber and exiting with the exhaust. This can be caused by worn or damaged piston rings, cylinder wall, valve, valve seats or some other internal engine issues.

Jul 31, 2016 | 2006 Chevrolet Cobalt

1 Answer

I'm looking to purchase a used car. I've been doing online research and saw this webpage http://www.usedcarsmells.com . They talk about exhaust color and smells. Is it true that you could tell a lot about the engine by looking at what comes out of the exhaust?

Yes this is correct, you can get important information from the colour of smoke from the exhaust:

Blue/Gray Smoke: Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/gray smoke at startup because oil leaks past the seals into the cylinder after the engine shuts down.
Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/gray smoke.
Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/gray smoke.
PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.
Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.
White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe.

Jan 17, 2015 | Cars & Trucks

3 Answers

would a defective fuel pump cause white smoke from exhaust?

probably not. White smoke in the exhaust is a sign of either coolant or oil entering the cumbustion chambers (cylinders). Faulty fuel pumps usualy stop delivering fuel to the engine and it won't run at all.

Aug 21, 2011 | 1988 Chrysler New Yorker

2 Answers

i ran my chev. 1990 pickup out of oil and now it smokes so bad. and i think my fuel pump is going out but not sure??

Sounds like you may have ruined the piston rings and this is allowing oil to seep in to the combustion chamber hence your smoke. Or if it overheated when you ran out of oil it is possible that you have a bad head gasket now. Check both your coolant and oil for signs, oil will have a white froth, or darkening of your coolant. Hope that helps you.

Aug 05, 2011 | 1990 Chevrolet C1500

1 Answer

97 kia sephia smokes when first starts, smells like exhaust smoke

Black smoke is fuel.
Blue is oil.
White is coolant / water.

Fuel is caused by timing and cold start system and requires some discussion to clarify.

Oil burning only on start is caused by failing rings on your cylinders. Oil then enters the combustion chambers and burns when you start the engine. If it continues to burn when running in particular when you accelerate it will also indicate ring/cylinder failure. It can also be from a failing head gasket where oil travels from the lubrication system into the combustion chamber. Some of the anti smoke additives available at the auto supply store do help.

I doubt you are seeing white as you say is smells like exhaust. White is coolant in the combustion chamber or exhaust system.

Hope this helps you.

Mar 11, 2010 | 1997 Kia Sephia

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