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How much silicone sealant will ruin the oxygen sensors?

I’ve just discovered that using high volatility silicone sealant not labeled as “oxygen sensor safe” on valve cover gaskets could contaminate and ruin the oxygen sensors. However, I just used a few small dabs around certain areas, not all the way around the cover, with some of the sealant having squeezed out from under the gasket. I was wondering if anyone out there has any information about just how much sealant can be used before problems with the sensors start to show up. Are a few small dabs OK? Should I take it in to have the oxygen sensors tested?

If the Check Engine Light illuminates, and the code is P030 to P0167 or otherwise indicates a possible oxygen sensor or even cat converter problem, you’ll have at that point established the level of silicone silastic that your car will tolerate. Test it then.

If you have no problems, than there’s no need to test it.

VALVE COVER GASKETS ? The valve cover gaskets and sealant have no relation nor nothing to do with each other nor can they share any contamination…there is no link between the two at all…and I’ve never heard such a thing in my life. I don’t think you have anything to be concerned about to be honest…

THE ONLY thing I have ever heard of in relation to any type of product compatibility and an O2 sensor in the same sentence… is the THREAD ANTI SEIZE that may be applied to the O2 before its installation…THAT product must be O2 sensor compatible and nothing else in regards to this issue… CERTAINLY not anything whatsoever about anything valve cover related…and the O2…they are Not connected in any manner nor ever will be.


Honda is right. I stand corrected. WHAT was I thinking?

If you do a search using terms like oxygen sensor contamination by silicone sealant, a lot of links will come up referring to the use of silicone sealant on valve cover gaskets as a possible source of oxygen sensor damage. This has apparently been a well known issue for decades, and is cited by several companies on their websites, including Bosch, which makes these sensors. I’m trying to find out how much is too much.

No kidding…Never ever heard of it… After pondering it, the only link I can imagine is from the PCV valve…which inhales and then burns crankcase vapors… That’s the ONLY thing I can think of…and even then I find that sketchy at best.

I go with Blackbird on this…it’s just not technically possible…urban legend stuff…

Seriously? A heck of a lot of engines have PCV valves right in the valve cover. If you lay a bead of RTV on the cover you can bet those vapors are going to be ingested and burned. The oil returns all go to the crankcase too. Even the manufacturers cite the risk but you don’t believe it? It’s one thing to expose ignorance and another to steadfastly cling to it.

To the OP, small dabs may not have any effect. TSM had good advice in his first post. The RTV cured in the first 24 hours. If no codes or unusual drops in fuel efficiency are noted, drive on.

Urban legend BS. If RTV was an O2 killer then this should mean that many GM cars would have wiped their O2s right after rolling off of the assembly line. Some may remember that GM did not even use valve cover gaskets; they used an overhead gun to run a bead of silicone only on the cylinder heads.

What’s probably happening is that by the time someone is dabbing some RTV on this means they’re dealing with a used, or well used, vehicle.
Problems continue, they have no idea why, and per the internet they’ve now found a villain.

RIF. RTV is an acronym for Room Temperature Valcanizing. There are many formulations of RTV sealants. It’s a certain TYPE of SILICONE RTV that affects the sensor and I’m pretty sure the GM engineers know which type to specify. Also, the GM stuff is designed to cure very fast to speed up repair time.

Like Twin Turbo says, there are different formulations. It appears to be the high volatility stuff with the acetic acid smell that’s bad, and can release fumes that get sucked in by the PCV valve. Sealant labeled “Oxygen sensor safe” are apparently low volatility and don’t give off as much of the fumes.

BTW, from what I’ve seen in my searches, it was GM that first discovered that silicone contaminates O2 sensors. Just a coincidence, or…?

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.

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.

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 true…it 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.


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.