Oxygen Sensors and Silicone Grease

[cookiemech]

Does anyone have any hard evidence that use of silicone (sometimes called "dielectric") grease on spark plug boots causes contamination of oxygen sensors? I have read numerous articles warning against using coolant with silicates, since minor head gasket leaks will cause that to be burned in the combustion chamber(s) and thus contaminate the sensor(s); also, I have seen warnings not to use non-oxygen-sensor-safe sealants on valve covers or anywhere that the vapors could be drawn into the intake side of the engine. Also, silicone sprays are considered unacceptable as those may be drawn into the intake.

But I have not seen specific warnings about using a bit of silicone grease to ease installation of spark plug boots (in my experience, it makes this process much easier and permits removal without damage).

What's bothering me is that I have three recent experiences with spark plug changes after which oxygen sensor failures occurred within 1000 miles: 2002 Tundra V8 with just over 90,000 miles, 2001 Sienna with just over 90,000 miles, and most recently a 2000 Hyundai with 93,000 miles.

Coincidence? The only place I used the grease was inside the spark plug boots (well, you know, on the Sienna and Tundra the tube extending down from the individual coil).

[Flashgordon]

I've never heard or read any hard evidence on dielectric grease when used on spark plug boots causes contamination of oxygen sensors. Actually the industry recommends that a "dab" of this grease be applied to the boot to aid in the conductivity and to seal out moisture.

Oxygen sensors, as you know go through extremes. I think the mileage you show of failures is about right and has nothing to do with spark plug replacement or the use of dielectric grease on the boots.
Coincidental?
I think so.....

[Cali-Tundra]

using dielectric grease on the boots should have no effect on the O2 sensors...silica based products, such as coolant, will cause contamination of the O2 sensors if they come in caontact...you can still use the same coolant, but if you ever have a head gasket leak and get coolant in the exhaust , you should also replace the O2 sensor(s)...and i would not recomend using any kind of silcone on the threads of the sensors either...hope this helps

[ddvk]

There is no truth to all this stories.

If you are that apprehensive about anti-sieze messing up O2s (which I don't believe), then put a tab of engine oil on the threads while replacing. This is what it is recommended by some .... But then there is nothing better than anti-seize!!!

[Cali-Tundra]

Originally Posted by ddvk

There is no truth to all this stories.

If you are that apprehensive about anti-sieze messing up O2s (which I don't believe), then put a tab of engine oil on the threads while replacing. This is what it is recommended by some .... But then there is nothing better than anti-seize!!!

I wouldnt consider Anti-Seize to be silicone, which is what i was talking about....
And if you say "there is not truth to all [these] stories," then why dont you correct it!

[DevinSixtySeven]

not sure i understand where youre putting the di-grease...you mean youre putting a film over the outside of the coil, or putting the grease on the head of the spark plug to keep water from getting between the plug and the coil?

ive always used antisieze on the plug threads but i dont think that's what he's on about.

i didn't know it was industry recommended practice to use dielectric grease on the plug/coil interface. i suppose it also would make sense to use it where the coil seals to the block, is this ok as well or will the grease heat/smoke/etc? ive had water down the spark plug wells before.

-sean

[cookiemech]

I use a small amount of dielectric grease between the spark plug boot and the insulator on the spark plug, the purpose being to facilitate installation of the boot. What I am imagining happening is the extremely hot environment around the spark plug vaporizing a bit of the silicone grease and that vapor finding its way into the induction system and contaminating the oxygen sensor(s).

Also I use a small dab of anti-seize paste on the spark plug threads, but I wasn't concerned about any effects from this (I've never heard that this poses a problem).

[LIMITED]

Originally Posted by cookiemech

Does anyone have any hard evidence that use of silicone (sometimes called "dielectric") grease on spark plug boots causes contamination of oxygen sensors? I have read numerous articles warning against using coolant with silicates, since minor head gasket leaks will cause that to be burned in the combustion chamber(s) and thus contaminate the sensor(s); also, I have seen warnings not to use non-oxygen-sensor-safe sealants on valve covers or anywhere that the vapors could be drawn into the intake side of the engine. Also, silicone sprays are considered unacceptable as those may be drawn into the intake.

But I have not seen specific warnings about using a bit of silicone grease to ease installation of spark plug boots (in my experience, it makes this process much easier and permits removal without damage).

What's bothering me is that I have three recent experiences with spark plug changes after which oxygen sensor failures occurred within 1000 miles: 2002 Tundra V8 with just over 90,000 miles, 2001 Sienna with just over 90,000 miles, and most recently a 2000 Hyundai with 93,000 miles.

Coincidence? The only place I used the grease was inside the spark plug boots (well, you know, on the Sienna and Tundra the tube extending down from the individual coil).

I should be ok I use it on all plug wires.