Caulking/Silicone smell when starting truck....?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by dock420, Sep 17, 2013.

  1. dock420

    dock420 Member

    I have a 2011 Chevrolet 1500 crew cab with about 31k on the clock. During hot days or when I first fire the truck off, I get a smell like caulking coming from the vents. It seems to subside once I start driving and have the a/c on the fresh air setting. This has been an issue for some time now, but seems to be getting stronger each day. No leaks under the truck when parked and nothing is wet inside the cab area. I have not used any caulking or silicone in or around the vehicle. I know diagnosing an odor is about as easy as winning the lottery, just wasn't sure if anyone has heard of this problem.

    Just to add, there have been no engine mods to the truck....

    Thanks in advance
    Last edited: Sep 17, 2013
  2. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Your truck sounds too new for my suggestion to be the problem, but here goes.

    The HVAC box under the dash has a vent hose the should expel water when the ac is on. sometimes the hose will plug and the moisture can not escape. When this happens, mould will grow inside the box. The blockage needs to be removed and there is usually an access port under the dash where you can get a mould killer sprayed into the HVAC box.
  3. j cat

    j cat Epic Member 5+ Years 1000 Posts

    sometimes things get into the air box. depends on where you live. lizards and other critters. where I live you have the tree pollen . since I live in the deep woods lots of that need be cleaned every spring or I get odor.

    also I would remove the fan assy and inspect for debris. clean off the fan fins and wipe down the box. check the blower resistors in there for organic material on the surface .

    the smell could be from the electrical connector for the fan/blower speed. some have had corrosion issues....
  4. dock420

    dock420 Member

    **UPDATED** Caulking/Silicone smell when starting truck....?

    So I took my truck in for state inspection, replace the crappy doors that cover the USB/Outlet and I mentioned the odor issue. Just drove back with the truck and figured I would update. They re-flashed the ECM with a current update (drive-ability issues), fixed the other items and....As far as the smell, they advised me that there was mildew in the A/C case and they activated the "After blower" feature. With that feature "on" it allows the blower to run after the truck is turned off in order to dry any condensation. I guess my question is, why don't they just turn that feature on at the factory, or is the problem specific to high heat/humidity areas? Just seems easier. Anyway, thanks to the above replies, and the help I get from this forum....
    Last edited: Sep 19, 2013
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    remember water alone does not smell ! what you have is organic goo in the box.....true reducing the water left in the box will reduce odor. the debris will in time effect the ability of the evap to properly absorb the heat from the hot moist air. also the drain gets restricted which could also be your issue now... the evap with debris in the box can cause the evap to freeze and then after a long operation in very humid conditions you will have little air flow. I would clean the box out and avoid parking under trees and other areas of debris that will get sucked in .. also vacuum the air intake screen of the hvac often ..
  6. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Thats good info about the "After Blower", I have a 2011 also, over the last 2 years each sping Ive had to open the evap box and clean out mold to prevent getting a musty smell at start up.
    The issue concerned me since I have other vehicles that are over 10 yrs old and have never had this issue.
  7. GM Customer Service

    GM Customer Service Epic Member 5+ Years 500 Posts

    Oh no! I am sorry to learn that you are experiencing a weird smell when you are starting your vehicle. I am not equipped to give any technical advice but I am happy to assist with any concerns or general questions you may have about GM products.

    Best Regards,

    Jennifer T.
    GM Customer Care
  8. Backroads

    Backroads New Member

    I have a 2010 extended cab Silverado LT and just recently noticed same oder the oder is not a musty or mildew type smell but very sharp and astringent like dock420 suggested fresh PVC caulking chemical smell.
  9. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Most service manuals have instructions for removing the mould.

    There is/should be an access panel on the HVAC assembly (under the dash) where the cleaning solution can be used.

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