TS2008

I just want to share the mistake I did, so don't make the same mistake.


To make a story short, I always has this habit to lubricate all rubber washer or o-ring with silicone grease. I got this habit while I was working for an R&D center. The problem is I just learned by accident that the silicone, even a tiny quantity, can harm the oxygen sensor.


Since I had removed the valve cover several times because of my timing belt issues, I lubricated generously the spark plug washers and the cover bolt washers with the silicone grease each time when I replace the cover back. Now I'm pretty sure that engine oil is contaminated with this silicone grease and my engine burns little oil (1qt/2k miles). So If I want to save my two oxygen sensors, I need to remove the cover again and clean all these washer and change the engine oil as soon as possible.


Anyways, just want to share my mistake.

RIPSAW

Would you not think the oil has washed off the silicon on the inside area of the gaskets by now and at best a couple oil changes would suffice? Just what does the silicone grease do?
Coat the oxygen sensor? I have hear undercoating can kill a sensor or even heavy caked mud on it?

ezone

Basically. Silicone is a poison to the sensing elements of an O2 (or similar) sensor. Silicone sprayed into the intake or engine oil contaminates it from the exhaust side of the sensor.




If one coats any of the sensor related electrical terminals in dielectric (silicone) terminal grease, it can contaminate and kill the sensor from the inside.
(see below)

Used to be that way, back when sensors had a fresh air sampling port on the body of the sensor itself, open to the outside fresh air. Most single wire sensors were built this way for sure.

Much newer O2 (et al) sensors tend to draw their fresh air sample through the wiring, "wicked" through between conductor and insulation. Much harder to kill but not impossible.

I have witnessed more than one newer sensor (within the last 15 years or so) contaminated or rendered 'stupid' (temporary or permanent) by brake cleaner or gasoline spills on the outside of the sensor, so some may still draw fresh air at the sensor itself..

TS2008

I use Dow Corning high vacuum silicon grease. It protect and "rejuvenate" rubber. I love this grease because it is very resistant to elements and pretty "stubborn" . This is the reason why I have to remove the cover again and clean the rubber washers.


My plan for the engine oil is I'm going drain the oil and replace it with a cheap oil. I then drive the vehicle for about 500 miles and drain the oil again and send a sample of oil to Blackstone for analyse. I found this procedure for silicone contamination analyse in the net. I can accept the fact that my two o2 sensors are going to die soon. But I have make sure the new sensors won't die prematurely.