FIA Expansion Tank question, regarding overflow
 

I have seen lots of info on here and online about Harrison Tank plumbing to the motor, but I have a question I have not seen covered.

If I understand the operation of the expansion tank properly, I don’t think the overflow (radiator cap pressure release port) should be connected to an overflow tank with antifreeze in it. Because every time the motor cools and the cooling system retracts it continually draw from the overflow reservoir, backfilling the expansion tank, negating its whole purpose. So I am going to run the overflow tank dry, basically catch can. That way the cooling stays with the same water volume. If it does expand in the tank and run to the overflow, it will only draw back in to its original water volume.

Am I thinking this correctly?

The Harrison tank is how you fill the cooling system. You should not run it dry, as you risk getting air in the system as coolant constantly cycles through it. You should run it about 1/2 full. If there is significant coolant expansion there is a fitting below the cap that is where you connect a small hose to feed a catch can that you can place inside the fender of the passenger side.

Jim

No plans whatsoever to run it dry (not sure where that came from), It is positioned exactly halfway up the highest part of the cooling, there is no way it can run dry if the system is filled properly and it should stay around the 1/2way point. I am talking about the overflow out of the expansion tank (at the radiator cap pressure release port), instead of venting straight to the ground. I may not have been clear enough in the original post. The overflow out of the tank has to be a catch can only (instead of partial filled recovery tank system). if it is a partially filled overflow reservoir, it will keep drawing filling the expansion tank higher and higher (during cooling/contraction cycles), basically negating the expansion tank's purpose.

Two different things in my post.
the Harrison Tank is the expansion tank, it is positioned 1/2 way up to the cooling system components.
The overflow I am talking about is simply to catch and recover overflow, if the expansion tank overflows. It shouldnt do anything when everything is working properly (no blown head gasket etc.)

It makes most sense to simply run the overflow/catch can (under the fender) completely dry. right, as you said. Even if plumbed as a recovery, it will draw back in what it expelled refilling back to the original level. It (the overflow tank, not the Harrison tank) has to be run dry for the Harrison tank to work as intended.

Here’s how I set mine up. Running it to an overflow tank, but the Harrison tank is only filled to the specified level (half way). I would agree, in theory you don’t need an overflow tank, but I think at minimum, it would need to breathe a bit / have a catch can.

Not sure how to better size the pic, sorry!

https://i.imgur.com/hTbxpvz.jpg

That helps clarify things a little better, in the first post it sounded like you were going to run the expansion tank dry. Your expansion tank sits lower than mine, mine is the upper most piece of the cooling system and sits on top of the transverse leaf springs tower. If you plumb the hose to the catch can into the bottom of the can it could get sucked back into the Harrison tank, if you plumb the hose into the top of the catch can it will not suck anything back into the Harrison tank unless the catch can gets filled to the level of the hose entering it.

My Harrison tank is the highest point as well. It has to be, if the halfway point of the Harrison is same height as the highest part of the cooling system (upper radiator hose). My guess is mine is mounted near same height as yours. The radiator cap is about 1” below that part of the hood.

You commented about, Expelling into top of catch can. That’s just it, if it does expell into the overflow/catch can, I do want it to recover it. Otherwise the level
of coolant in the system just dropped that amount, just like it did years ago. So you can plumb into the catch can so it can recover the expelled amount; but only that amount.

In these posts I feel I’ve answered my own question. The catch can (recovery, in
my case), must not filled with any additional antifreeze.

Yes, Buddy, you are correct in that the catch can is there only to prevent excess fluid from leaking onto the road. The Harrison tank is for holding normal expansion of fluids. It is interesting how differently the expansion tanks can be plumbed. Mine is way different than yours.

http://www.clubcobra.com/forums/pict...=20997&thumb=1 http://www.clubcobra.com/forums/pict...=20998&thumb=1

Is your concern theoretical (this may happen), or have you had issues with the coolant in the Harrison tank overfilling it and dropping it on the road? In all the time that I have raced mine I have only had a small amount of water get deposited in the catch can.

Good luck.

Jim

Actually, mine will be plumbed exactly like yours. Lower inlet Of the expansion tank is plumbed to the block. In my case, one of the water pump heater hose outlets.
The upper vent port (not the radiator cap pressure release) is plumbed to a high spot in the cooling system so hot air can be exchanged and equalized between the
expansion tank and the cooling system. In my case, I’ll tee in to the upper radiator hose, yours goes to the top tank. And the radiator cap pressure release port goes to the catch can.

No, I Do not have problems currently. Just adding the Harrison Tank
to Match the authentic race cars (FIA, USRRC, etc). I’m just trying to cover everything. I’ll finish it this week schedule permitting.

Is yours an original? or a modern CSX? either way, nice. Id love to do some webers. For now Ill have to stay with my C9OX Ford Intake and 650 DP.