Coolant System Overflow Tank

Mark Setter

Silver Supporter
I am working on the details of the cooling system and have the pressurized "Header" tank worked out. In looking at the overflow tank, I have a -4AN fitting going to a 1/8th NPT at the top of the tank, and a drain at the bottom. Shouldn't there be a hose connected to the NPT thread going to the bottom of the overflow tank in order to allow for the return of coolant when the system cools down? If so, where is the source for that tubing?

Ken Roberts

Active Member
Mark some of the overflow tanks have a tube inside that fitting at the top that goes to the bottom internally. My Moroso overflow tank is like that.

Mark Setter

Silver Supporter
Thanks for confirming that, Ken. I did not get that tube, but I can contact them for one. It makes sense that you could draw from the bottom by having a bottom mounted fixture, as was suggested, or have a tube come from a top mounted fixture. I would prefer the top mounted fixture, keeping the ability to drain the tank form the bottom if needed.
What if your radiator doesn’t have a bleed line port. Where can you add a bleed line in the system?

Is there a height you need to mount the recovery tank?
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The bleed line must be located where a possible air pocket may develop (top area of rad). You can buy a NPT weld in bung and drill a hole for it. Then take the rad to a welder.

Mark B.

Bronze Supporter
Steve, if your radiator is like mine, you have a drain petcock on the bottom and another one on the top driver's side. You can remove the top one and thread in an NPT hose adapter for the vent.