Join the Car Talk Community!

Discussion Rules

Welcome to the Car Talk Community!

Want to ask a question or join the discussion? Great! Join now.

Sign In Register

How much silicone sealant will ruin the oxygen sensors?



  • The highest temperature RTV I've ever seen is rated to maximum temperatures of 650F, I don't believe any silicone silastic can withstand the temperatures of combustion chambers, which can exceed 2000F.

    I agree with those that say it's a myth. I don't see any way that fumes from curing silicone RTV can get through the combustion chamber and coat an oxygen sensor. If one were to suggest that it coated a component that precedes the combustion chamber I might accept the possibility, but not an oxygen sensor.

    If there exists actual data from a credible source, I'd be interested in seeing it.
  • I also can't understand what vapors would come off curing RTV that could survive a trip through the combustion chamber. In addition to being burned up, it would be diluted by a million to one (or more). I'm pretty sure any acetic acid fumes would be consumed.
  • I was also skeptical at first, but searching the Net convinced me that there is something to it. GM discovered it. Even Bosch, which makes these sensors, warns about it. From what I've read, these things work on a molecular level, so since I don't have a good understanding of chemistry, etc. etc., I'm just going to play it safe and use the "oxygen sensor safe" stuff in the future.
  • edited January 2012
    There's a big difference between what I don't understand and what's correct. I'd follow Bosch's instructions, too.

    Great user name, by the way.
  • The exhaust gas volume is so large, the amount of silicone "vapor" is so small....It's not like you were squirting the silicone right into the intake manifold of a running engine...What little "vapor" there is, most of that tiny fraction will be absorbed by and dissolved in the motor oil and held there until the oil is changed..This is a tempest in a tea pot...
  • I don't buy into silicone sealer killing O2 sensors for one second. As I mentioned, by the time someone is gooping up oil pans, valve covers (possibly in tandem with a head gasket), and so on that tells me someone is dealing with a high miles or problematic engine. Any O2 problem is likely related to the engine problem.

    Now why would sealant manufacturers have a disclaimer? To weed out the possibility of the ever present lawsuits and sniping where someone claims that silicone killed their 150k miles oil burning motor.
    Look at the mountain of grief that Fram goes through over countless internet stories about their oil filters being faulty.

    Class actions suits are filed for a lot less reason than the above. My mind is subject to change if someone could provide one verifiable case of an O2 being murdered by silicone.

  • edited January 2012
    I guess all of us mechanics have just "EXPOSED OUR IGNORANCE".......I feel so ashamed. I still have difficulty buying it, but I'm listening....I thought that was obvious. I STILL don't fear this much, sorry, I don't. What could possibly make it through the combustion chamber FURY.....and then have enough spunk left to mess with your O2? MAYBE something? Dunno...again.....having hard time with this one...... But if its goes in my notebook as NEW INFO. I guess that goes against the "Steadfastly clinging to my ignorance"....doesn't it?

    At least I caught myself and said that the "link" is thru the PCV valve....and I have a thorough understanding of whats what under the hood, whatever it is...Its a new one on me. Said so in my post.....How Ignorant of me...I'm a moron

  • Some types of RTV were labeled "Oxygen sensor safe" in the '80s and '90s. I think all automotive engine RTV is oxygen sensor safe now. There were many warnings about this back then.

    Here is a Volkswagen bulletin;

    Group: 26

    Number: 93-02

    Date: July 31, 1993

    Oxygen Sensor Contamination Due to Silicone

    All Models, All Model Years

    (Supercedes Technical Bulletin 92-01, Repair Group 26, November 30, 1992)


    Do NOT use any sprays or compounds containing silicone on engines equipped with Oxygen Sensors. Do NOT use these compounds on or near the intake air system or near the Oxygen sensor. Silicone drawn into the intake air system is not burned during combustion and will lead to contamination and malfunctioning of the Oxygen Sensor.
  • GM;

    Model Year: 1981

    Bulletin No: 81-I-37

    File In Group: 60

    Number: 11

    Date: Feb. 81

    Silica Contamination of Oxygen Sensors and Gelation of Oil.

    Models Affected:

    Oxygen sensor performance can deteriorate if certain RTV silicone gasket materials are used. Other RTV's when used with certain oils, may cause gelation of the oil. The degree of performance severity depends on the type of RTV and application of the engine involved.

    Therefore, when repairing engines where this item is involved, it is important to use either cork composition gaskets or RTV silicone gasket material approved for such use. GMS (General Motors Sealant) or equivalent material can be used. GMS is available through GMPD with the following part numbers:

    1052366 3 oz.

    1052434 10.14 oz.

  • I checked out the Permatex site for info on the various types of silicone sealants. I think Nevada_545 may be right about most automotive RTV's being sensor safe these days, at least in the case of Permatex. Nearly all of their engine sealants are described as being "sensor safe", EXCEPT the Red High Temp RTV Sealant, which, of course, is what I used. Again, I hope those few small dabs weren't enough to toast my O2 sensors.
This discussion has been closed.