Expansion Tank

My main engine is cooled with a keel cooler welded to the hull. Because coolant will expand as it warms up to operation temperature, I needed to give the coolant a place to go without building pressure on the system and causing the fill cap to burp off coolant.

The expansion tank is at the highest elevation of the cooling system. This will allow me to get air out of the system and also use the expansion tank as the fill point for the cooling system. I made the tank out of a 12" piece of thin walled pipe. Welding a place for the pressurized fill cap, end caps, mounting brackets, level check sight glass, connector fitting on the bottom, and drain fitting on the bottom plus and extra fitting on top was all it took to make the tank. Well I might as well throw in finding the pipe, getting the pipe, cutting the pipe, cutting the end caps, fabricating the fill neck and mounting brackets, air testing, sand blasting, and painting. Now that I think of it, building the expansion tank was a pain in the ass, and if I had to put a pencil to it, I'd say I have 12 hours in it. I could have purchased one for a dump truck for about $250.00 but given my nature of tripping over a dollar to save a dime, I decided to fabricate mine.

I Installed a sight glass in the tank to make checking fluid level easy. Due to height constraints, peering down the fill cap would be difficult, a dip stick would be a pain in the ass, so the sight glass, hands down, is the way to go.

I built the tank a couple of years ago, and now that I have the engine room finished sheathed, I can go ahead and permanently mount the tank. I was able to make the permanent connections to the keel cooler from the engine, and also all the connections to the expansion tank.

I mounted the tank to the bulkhead by using studs welded to the framing. I messed up on one set in regard to how far the studs projected and ending up having to use couplings on the studs then bolting the tank to the coupling. I wanted every part of the tank to be higher than the engine coolant tank, and while I was cutting it close, all the elevations worked out fine. The street 90 at the bottom of the tank is 3/4" higher than the street 90 in the engine.

Oh how nice it is to finally see projects going from the shop shelves to their final resting spot on the boat.