I just want to add to this as I've been digging for flight worthy 02 sensors for an auto conversion. The O2 sensors get coated with lead, that's what 'kills them'. They cannot detect the O2 level in the exhaust as the lead literally covers the sensing probe. Its not a like a chemical reaction is 'eating away' the metal, its still there, buried under a coat of lead. The same thing that lead does do spark plugs. It doesn't eat the plug or corrode it, it just fouls it. Just google 'lead fouled spark plug' and be amazed. From Shells web site: "The Tetra Ethyl Lead used for octane boost in the fuel naturally degrades to form Lead Oxide when it is burned. In reality it is this oxide which gives the octane boost. The problem is that Lead Oxide is a solid up to about 900 deg C which is well within the wall temperatures inside a piston engine. In order to prevent these deposits from forming, a Lead scavenging compound is added to Avgas 100LL - this compound is Ethylene Dibromide. This scavenger is designed to react with the Lead oxide to form Lead Bromide which is more volatile - becoming a gas at around 200 - 250 oC. This is a low enough temperature to ensure that the Lead is removed from the engine as a gas end it subsequently goes back to the solid phase as the exhaust gas cools in the atmosphere." From wiki: "Leaded gasoline contaminates the oxygen sensors and catalytic converters. Most oxygen sensors are rated for some service life in the presence of leaded gasoline, but sensor life will be shortened to as little as 15,000 miles (24,000 km), depending on the lead concentration. Lead-damaged sensors typically have their tips discolored light rusty." But 100LL has 8 times the amount of lead that car fuel does. So even if you get the bare minimum of 15,000 miles (at 60mph that's 250 hours, 1/8 of that is 31.25 hours). So you could most likely find an O2 sensor to last a 'normal' flying season, to be changed at the annual. So it would appear that if you put the O2 sensor in a location that keeps it hot, and the additives in 100LL keep the lead gaseous. Now could you move the pre-cat O2 sensor close enough to the exhaust valve where the TEL is still gaseous? And will it survive the higher temps? Most O2 temps need to be at 300C+ to work, well above the 200-250C gaseous Lead Bromide temp. Would a 20 or 50 hour remove and clean be enough? Or even just replace the sensor every 25 hours (I dare say most non-school planes don't fly that much). O2 sensors are $30-ish each. $60 per oil change is not a huge amount of money. Ninja edit - NO, I DON'T WANT TO HEAR ABOUT RACE ENGINES. They are highly modified to burn much more gas to create much more power. And who knows what 'tricks' they incorporate to run the 8-10 laps on a short track.