can anybody tell me what sensor is this or whats the thread pitch? I pulled it off from back of the block next to the oil pressure sensor off a b18a1 block. Ive included a diagram below. When looking at the diagram its suppose to be a plug but previous owner had this on and where the oil pressure sensor goes they used a T and used it for something else. I just wanna know what sensor and theead pitch so I can buy a plug and block it off. Thanks in advance.

 

looks like an aftermarket oil pressure sensor

 

They were using that as a block breather. Looks like they plugged it with some random sensor they had laying around.

 

That is the fan switch found on the early B18A family of engines... the B18B family moves this switch over to the thermostat housing and changes the sensor type to one with a two pin round grey plug instead of the dual male bullet style connectors like you have pictured. Do not focus on the thread pitch of the sensor itself, rather, remove the entire large hex and replace it with the same location fitting from a newer B18B block.