I had the same blower on my car and that is the fill hole. Down the front of the case behind the dist. you will see another plug. That is the level plug for the oil. If you over fill the blower then it will blow out the front seal after a while and lose all the bearings and cause the rotors to smack together. Not good! If I remeber correctly you only need about 4 oz of 90w oil to fill it. I use to use B&M trickshift tranny fluid instead and that will filled an extra 2 oz because of the light weight.