How much silicone sealant will ruin the oxygen sensors?

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

Blackbird

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

Subject:
Oxygen Sensor Contamination Due to Silicone

Model(s):
All Models, All Model Years

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

CAUTION

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

Subject:
Silica Contamination of Oxygen Sensors and Gelation of Oil.

Models Affected:
All

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.

Good info from VW & GM. Thanks, Nevada_545.

Ford;
11/10/93

^ EGO SENSORS - SILICONE CONTAMINATION

^ ENGINE - SEALANTS, LOW VOLATILITY SILICONE REQUIRED

^ EXHAUST SYSTEM - SILICONE CONTAMINATION OF EXHAUST GAS OXYGEN (EGO) SENSORS

FORD:
1984-86 LTD
1984-88 EXP
1984-94 CROWN VICTORIA, ESCORT, MUSTANG, TEMPO, THUNDERBIRD
1986-94 TAURUS
1988-93 FESTIVA
1989-94 PROBE
1994 ASPIRE

LINCOLN-MERCURY:
1984-86 CAPRI, MARQUIS
1984-87 LYNX
1984-92 MARK VII
1984-94 CONTINENTAL, COUGAR, GRAND MARQUIS, TOPAZ, TOWN CAR
1986-94 SABLE
1988-89 TRACER
1991-94 CAPRI, TRACER
1993-94 MARK VIII

MERKUR:
1985-89 XR4TI
1988-89 SCORPIO

LIGHT TRUCK:
1983-94 RANGER
1984-90 BRONCO II
1984-94 BRONCO, ECONOLINE, F-150-350 SERIES
1986-94 AEROSTAR
1988-94 F-47, F-53
1991-94 EXPLORER
1993-94 VILLAGER

This TSB article is being republished in its entirety to update model applicability and to revise the part number of the Low Volatility Sealant.

ISSUE:
EGO sensors can be contaminated if volatile types of silicone are used when servicing the engine. Volatile silicones can migrate throughout the system during the first one hundred hours of service. They are commonly found in liquid “silicone rubber” sealants and gasket material. These products are commonly sold in tubes and caulking-type cartridges.

ACTION:
When service is performed on the engine, only use new low volatility silicone sealant (F1AZ-19662-A) where specified. Also replace the contaminated EGO sensor if required.

CAUTION:
DO NOT SUBSTITUTE CONVENTIONAL SILICONE RUBBER SEALANTS WHEN LOW VOLATILITY SILICONE SEALANT IS SPECIFIED.

PART NUMBER PART NAME CLASS

F1AZ-19662-A Low Volatility RTV Sealant B

For a very very long time…I have been using Ultra-Black…by Permatex… In the very old days I DO remember using a really really stinky type of Silicone…it STUNK…esp when curing…I bet that type is the one we are talking about…

I basically never even come into contact with that stuff…not for the last 15 years at least…Always hated that crap…That MUST be what we are talking about…

I am GUESSIN that Ultra-Black is O2 sensor approved…but I am guessing based only on my Schnoze…Nariz…BIG FAT NOSE… I could be wrong, but I don’t theeenk so I will check…

Blackbird

They still sell all of the old formulations, you just haven’t seen them because you’re shopping for them at Autozone. There are literally hundreds of formulations available, we use a dozen or so for various purposes at work. Many of them outgas nasty fumes that affect sensitive electronics. Just because you don’t understand how small amounts of these vapors can survive the combustion process and have an affinity for the materials in the O2 sensor doesn’t mean it isn’t a fact.

I guess all of us mechanics have just “EXPOSED OUR IGNORANCE”…I feel so ashamed

Not all of the mechanics have exposed their ignorance HB. But several prominent (and more vocal) ones that frequent this site have. That’s the really scary part for people who might be looking for advice or even worse, work to be done.

It is not a question of volatility or curing time of some silicone sealants that leads to O2 sensor failure.

From a tech course manual from a major car manufacturer (which is copyrighted and which I don’t have permission to copy):

“When silicone burns in the combustion chamber, it causes a silicon dioxide glaze to form on the oxygen sensor. This glaze causes the sensor to become sluggish when switching from rich to lean, and in some cases, increases the sensor minimum voltage on the lean switch. This causes the fuel system to spend excessive time delivering a lean mixture.”

The SiO₂ deposits on the sensor are either a white glaze or a light gray dust, quite distinctive from other deposits that cause O2 sensor failure.

This outgassing of SiO₂ particles continues long after the sealant has cured, and occurs whenever high temperatures are present.

“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 GM engineers most likely discovered the issue while trying to find a silicone sealant to use as a gasket material. They tried a number of materials and discovered that some caused sensor problems, then deduced where the problem came from. They shared their knowledge with the public to keep us from snuffing out O2 sensors.

Yeah your right TwinTurbo…since I (and or we) didn’t know about an issue brought to light some 15-18 years ago and learned something from this post…IT IS TRULY SCARY that we take time out of our days to help people… I shop at Autozone? Didn’t know that…I thought I used my warehouse that supplies most of the East Coast…I buy wholesale as a shop owner…mite hit Autozone for an air freshener?

Since some of us didn’t know about a rather obscure issue with Silicone sealant and O2 sensors…our FUTURE advice on ALL other automotive issues should be discarded and round filed…Especially MINE since I actually admitted to NOT hearing about it before and sat back and was HAPPY to be educated…I’m a real hard case man…hard to get along with…hard to teach…and IGNORANT…You got me man…hit it right on the head.

You remind me of some BAD TEACHERS I have encountered in my lifetime…Ones that made people feel bad or STUPID about not having the right ideas about certain things… Ones that look down on people for knowing something that they don’t. I have always lived by the motto of “You can learn something everyday…from ANYWHERE”

Even when I Admitted my ignorance you took it a little further to berate me…You seem like a real CLASS ACT brother man.

I look forward to learning more from life and maybe this site…I learn something everyday… What I don’t get is people like you…

SO I have an announcement…to all here… MY LIFETIME OF KNOWLEDGE ABOUT CARS IS ALL NULL AND VOID BECAUSE I DIDN’T KNOW ABOUT SOME SILICONE VAPORS HARMING AN O2 SENSOR…PLEASE IMMEDIATELY DISCARD ANY INFO I MAY GIVE TO YOU…FOR FREE…AND ON MY TIME…AND DIME…I’M A TOTAL AUTOMOTIVE QUACK…AND KNOW NOTHING ABOUT ANY VEHICLE RELATED ISSUE…APOLOGIES IN ADVANCE.

Blackbird

INCIDENTALLY…while I was visiting a Sage Mechanic friend of mine…Spurned by this post…I asked him… “Hey have you ever heard of Saaay…Silicone Sealant…used on a valve cover gasket actually affecting an O2 Sensor?” His IMMEDIATE and confident response was…“YEP SURE HAVE!!” I laughed and said “really”…Yeah sure he says…He also mentioned it was quite some time ago when he worked at so and so…and he specifically recalled the RASH of issues experienced during his tenure at this dealership… I was impressed and listened and learned…He also was happy to spread the knowledge…he didn’t look down on me… It was a nice learning experience…and I sat and listened and believed the info…

I think maybe I have been lucky by always using an exempt type of product (O2 safe) without the possibility of doing any damage…so even though I never knew about it…and NOW I DO recall seeing it on the packages…DUH! In fact I have seen this written on SO MANY packages of the stuff…I think I just stared at the words and didn’t read them nor try to grasp WHY they would write this on the stuff… One of those weird things I guess… Like I said…I learn something EVERYDAY…and am grateful for it. Learn on…

Blackbird

So the acetic acid that makes some RTV stink doesn’t survive the combustion chamber.
However, silicon is an element and it does survive combustion…
It starts out as Acetoxysilane, not SiO2 (which is basically glass) when it’s in the RTV
It gets oxidized in the combustion chamber. Carbon and hydrogen atoms get stripped away and replaced with oxygen.

Do they claim that RTV will emit enough O2 killer even after it dries? I mean, it dries quickly.

Jeff, Malty tasker has not been here in 7 years. There are plenty of current threads that can be answered.

It depends on which silicone you are talking about. Acetoxy curing silicones never completely cure, especially if they have some thickness to them. This is your typical first generation silicone, and may still be available for caulking. You might find a data sheet on the silicone you want to use, and if it uses a catalyst to cure, it should cure completely.

Now that we’ve dug up an old discussion . . .

You can still buy those stinky rtv gasket makers at 99 cent stores

They come in a very small tube, probably meant for one-time use