I have a 2011 GMC Sierra 1500 V6 with 145,000 miles. For about the last 6 months or so when I start the vehicle after it's been sitting for a while, a very large plume of white smoke belches out from the tail pipe. It's a very large cloud that lingers and will float away with the wind, it doesn't dissipate quickly. Fearing a head gasket I took it to a mechanic when it stated which they advised they see the smoke but couldn't track down the source and "would hate to tear apart the engine for no reason". There's no check engine light on FY.

Fast forward to about a month a go I took it to the mechanic again for an oil change and again to check the smoke plume which I recorded and showed the mechanic. Again, he said he didn't want to tear apart the engine costing me a ton of money with no definitive reason for the smoke.

Recently a new symptom has developed, a seemingly lack of power especially when at start up when I press the gas but not so bad once it's been running. Also, my gas mile has gotten really bad. I commute a distance to work daily and have use about 1/2 tank but now seem to use almost 3/4 in the same period.

At this point since I've been to the mechanic twice I'm at a loss. Thinking about a second option at a different mechanic but thought I'd check here first.

Thanks for reading and any feedback!

  • It is oil burning, more than likely you need new Valve stem seals, not a big repair.
    – Moab
    Commented Jun 23, 2017 at 23:36
  • Thanks - someone else said value stem seals I spoke to personally. Not sure if it helps or not but it only smokes upon start up after it has sat for a while - over night or while at work for example. If I start it now and then again an hour, it won't smoke. Also, doesn't smoke while driving. Thanks again!! Commented Jun 24, 2017 at 0:35
  • Classic valve stem seal issue.
    – Moab
    Commented Jun 24, 2017 at 0:37
  • 1
    Not anymore, with much higher combustion temperatures and catalytic converters, it will be white.
    – Moab
    Commented Jun 24, 2017 at 14:06
  • 1
    The smoke is the magic leaving the automobile. Commented Nov 21, 2017 at 2:51

5 Answers 5


White smoke generally has two causes; a thin white smoke that disapates quickly is just condensation in the tailpipe, and is nothing to be worried about. A thick white smoke that lingers indicates that the vehicle is burning coolant - which in most cases, means that you have one of a blown head gasket, a damaged cylinder head, or a cracked engine block. None of these is a cheap fix.

Given the other symptoms; lack of power on startup - I'd be leaning towards a blown head gasket, which means one (or more) cylinders are down on compression, so not pulling their weight in hard acceleration. That would also account for increased gas consumption.

Diagnosing a head gasket isn't hard for a competent garage - I recommend you find one. Good luck!

  • Thanks - I thought it may be a gasket and was surprised the mechanic didn't jump to charge me. I guess that means he's honest but concerned that he can't diagnose it. Not sure if it helps or not but it only smokes upon start up after it has sat for a while - over night or while at work for example. If I start it now and then again an hour, it won't smoke. Also, doesn't smoke while driving. Thanks again!! Commented Jun 24, 2017 at 0:37
  • A mechanic should check for coolant in the oil, check for exhaust gases in the radiator and check for coolant in the combustion chamber. I'd probably run a compression test as well, but the sum of the first three tests will be conclusive, and take less than 15 minutes.
    – PeteCon
    Commented Jun 24, 2017 at 3:07

Actually brake lines often are only seperated by the shield near the fuel pump. I have seen this often. When the car accelerates leaking fluid would make contact with with the muffler from gravity and air pressure.

However, I have found more often than not the cause is fuel rail and injectors. Bleed fuel rail and check if fuel is brown or murky after sit times from poor performing filter on evap lines allowing dust to enter the tank or possibly open loop somewhere else in the system. Usually when it’s the head gasket you will know from performance. However in tricky situations look for steam in oil fill or air bubbles in a full closed loop coolant system. Again just going from my experience IRL


I have had that symptom before and all I remember was that I think I overfilled the oil and therefore it was burning oil not petrol and thus the mix was wrong which accounted for the lack of power. This was on a CBF125 at the time.


If the vehicle is using coolant with no evidence of a leak? Or there is white sludge in the radiator or oil, then I'm afraid either the head gasket has likely failed or there is perhaps a crack in a cylinder head etc.

You're likely using more fuel as you're down on power so using more throttle to compensate for the issue.

It is not uncommon to have a little white smoke/condensation from the tailpipe especially in cooler weather, but clouds of it can indicate a problem.

As you say this has been going on for a good while, then you definitely need a second mechanics opinion on this vehicle, before something possibly fails altogether.


Thick white smoke from tail pipe isn't always a bad motor it can be a master cylinder that is leaking You might want to look to see if your master cylinder is leaking from the seal when you brake hard all the way down and hold it down. the master cylinder serves as the main valve that pushes brake fluid through the brake line so that the brake calipers can squeeze the pads against the rotors so even though your not pumping brake the master cylinder is still pushing brake fluid through the brake line so if it leaking when you start accelerating thick white smoke will come out of your tail pipe but evaporates very quickly and then it will stop smoking. so check for leak in master cylinder one way to get a master cylinder to leak is when your trying to get air out of your line you have someone inside pumping the brake. one last thing your car won't lose any power if it is the Master cylinder but can,mess up other parts like your air mass flow sensor which would give the car bad mailage and drive bad

  • 1
    Eh? How do you think a leaking brake master would cause smoke to come from the tailpipe? There's no connection between them! It might make smoke from the brakes, if they were really sticking on badly, but that'd be really obvious...
    – Nick C
    Commented Aug 8, 2018 at 15:16

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