Sorry your mechanic friend was so surly - but hey, that's why you come talk to The Chemtooler, right? Silicone of any variety will contaminate the oxygen sensor. And the amount of silicone needed to do this is minuscule. How minuscule you may ask? A well known example is: Silicone-based RTV gasket sealants. These type of sealers outgas small amounts of silicone when they cure. If you use one of these sealers on an oil pan or valve cover gasket, the silicone vapor will be sucked into the crankcase ventilation system and then into the intake manifold. As a result, the oxygen sensor, once contaminated with silicone, will be inoperative within a day or two. Likewise, do not use silicone-based lubricants anywhere under the hood, or anywhere forward of the firewall. The following Berryman products do not contain silicone, and are safe for under the hood maintenance: -When cleaning your engine, use Berryman's B-33 Engine Degreaser (#1133). -When cleaning fuel-injected air-intake components, use Berryman's Air-Intake Cleaner (#2209 or #2630). -When cleaning any electronic switch or component; use Berryman's Electronic Cleaner (#2206). -When cleaning compressor or alternators, use Berryman's Electric Motor Cleaner (#1520). -When cleaning carburetor or other metal parts, use Berryman's B-12 Chemtool (#0116). -For any general-purpose under-the-hood lubrication need, use Berryman's Total Lube (#0612).