Its been a while since i have posted, and worked on the 55 3600. I have recently pulled the 235 out of the truck and have it on the stand for inspection, with the intention of resealing and replacing whats only necessary. The rear "petcock" which i believe is a water/coolant drain has been removed and is plugged so i will need to work on cleaning the passage ways which seems to be common. The thing that has me perplexed is the large pipe plug that is above it, which appears to be an 1 1/2" pipe plug with the square head on it. I have searched around and cant seem to find any info on this. The attached picture shows the plug at the rear of the engine (you may have to zoom in on this) keeping in mind the engine is upside down on the stand. Ive tried to remove this but it is seized solid. My question is what is behind the plug, and if i remove it would it assist me in cleaning the water passages?
