How to Install Headers on a Lexus GS300
A GS300 header will come out through the top, but the upstream oxygen sensor is the part that actually stops the job.
The Short Answer (TL;DR)
On this ClubLexus GS300, the header unbolts from the Y-pipe with three 14mm bolts and from the head with eight more 14mm bolts, then lifts out through the engine bay. The upstream oxygen sensor would not come off, even after heat and penetrant, so the installer planned to replace that sensor instead of saving it. Budget a 22mm oxygen-sensor socket, a half-inch breaker bar, and a new sensor before you start.
Tools Needed
- 22mm oxygen sensor socket
- 1/2-inch breaker bar and 1/2-inch ratchet
- 14mm socket (not a deep socket)
- 10mm deep socket
- 6-inch extension
- Penetrant
- Ramps
The Step-by-Step Process
Get the top of the engine out of the way
The strut bar, engine cover, and intake were already off in the write-up. Strut-bar bolts were 14mm. The engine cover used a 10mm.
Unbolt the Y-pipe
Three 14mm bolts hold the header to the stock Y-pipe. Two of them sit out of sight at the sides. They came off without a fight.
Unbolt the header
Eight 14mm bolts hold the header to the head. A breaker bar was enough. The header then pulled out through the engine bay, not from underneath.
Deal with the seized oxygen sensor
The upstream sensor, the one before the catalytic converter, would not break free. The first sensor socket broke. Warming the car and soaking the threads still did not move it. The plan was to cut the loss and install a new upstream sensor rather than keep fighting the old one.
Why You Should Upgrade While You're In There
The header is off and the upstream sensor is the part this job destroyed. Replace that sensor while the flange is open, and confirm the part matches your exact GS300 year and engine before you order.
Frequently Asked Questions
Does the header come out the top?
On this car, yes. Once the eight head bolts and the three Y-pipe bolts were out, it lifted through the engine bay.
What if the oxygen sensor will not unscrew?
Heat and penetrant were not enough here, and a sensor socket broke. Plan on a new upstream sensor instead of assuming the old one will reuse.
Source: ClubLexus header install write-up. Photos stay on that thread.
