expansion tank

[Frank Coppola]

OK fellas I need some advice. I recently installed an expansion tank on my ride. (It looks like the attached picture.) The expansion tank I installed has two small ports, one (port "A") is above the seal of the radiator cap to go to a catch can, the other (port "B") is below the radiator cap and would go to another expansion tank.

Question number one. Does a catch can have to be able to take pressure? My catch can has an non threaded 1" hole which I can place the hose "A" in, but the only way to make this can handle pressure is to weld a bung on it.

Question number two. What should I do with port B
(mulitple choice, 20 points for a correct answer)

a)- cap port "b"

b)- weld a second bung to my existing aluminum catch can and run ports A & B to it.

c)- leave my existing can as-is for A, and ADD a second expansion tank for B.

d)- run a 6AN line from the top of my water neck to port B

e) none of the above

I was going to pick "d" as I thought it would be easier to run a line instead of capping port "b". I didn't think another expansion tank was worth the $$$.

Thanks,

[Toivo]

the cooling system needs to be pressurized entirely, including catch cans. The catch can not only "catches" the overflow, but should return it to the system as things cool down. It can only do this if it is part of the overall pressurized system. I would expect the second Port to go to the radiator. The tank is needed on Cobras due to the usual fact that the radiator top is lower than the manifold and a "high" point is needed to fill things up.

Just my understanding of how things work.

[Zderf]

Catch cans are usually just that... they catch the overflow for the system when it gets hotter than its normal operating range. Then as the system cools it creates a vacuum that pulls the coolant back into the pressurized portion of the system.

Good catch cans (not the plastic ones) usually have a port on the bottom to which your port "A" should attach and often includes some sort of drain valve as well. They are vented at the top (so they are not pressurized) which vents air as the can is filled with coolant. Air then is drawn back through this vent when the system sucks the coolant back out and through port "A".

You really should not need another "reservoir" of coolant available to your pressurized system unless you've got an overheating problem that causes the "catch can" to discharge overboard thus loosing coolant volume. That problem should be solved with water pumps, radiators, and coolant mixtures.

Just an idea or two. Anyway... it worked for me.

Zderf

[bad_sss]

1. No pressure here; just give the overflow a place to go.

2. Plug it.

[Bob Putnam]

I think I'm getting a crick in my neck.

The fitting below the cap seal can go to an air bleed at the top of the radiator or the intake manifold, as long as the usual water level in the tank is higher than either.

[Frank Coppola]

Bob,

I was hoping you would reply as you have saved me in the past. Running a line from the 1/2 NPT fitting at the top of my water neck to the port B (below the rad cap on the expansion tank) is a bit redundant but it can't hurt. It's effectively the same as pluggin it as bad_sss suggested. This is a perfect example of spending too much time thinking about something- I tend to forget the rule of K.I.S.S.

Now, since you are an authority. Please explain this: The port at the radiator cap (affectionately referred to as port A in my case) would vent fluid when the system builds more pressure than the cap is rated for. Therefore, since there is a spring in the cap forcing the valve to close once the pressure is released, there is no way to recycle the fluid back into the system. Right? This was my understanding, but Zderf and Tovio say no.

Thanks guys!

[Whaler]

The radiator cap you choose is rated for so many pounds pressure. That spring therefore is the force the system pressure must overcome to pop off and spray green stuff on the ground at your next carshow. There are 3 common pressure caps. The cap, if and when it pops, will open from within and "vent" thru that small overflow and downspout. If you have a hose on it with a little length, it will at least go to either the catch can you speak of or to the ground in a more orderly and cleaner fashion.
Pressurizing our cooling system and using the 50/50 mix of coolant and water allows us to get the water above boiling point in terms of temperature but not allow boiling. We effectively raise the boiling point. Anything on this side of that open rad cap is non pressurized and likely piddliung into your catch can. If you have one, fine.

I was told by my rad guy that the level of the overflow should be just above the baffle plate. The extra space will allow for raising and falling when heating and cooling. aka "expansion"
This is also your high point in the filled system..allowing filling and venting of entrapped air.

I am throwing a nice length of whatever is handy and looks nice onto that niipple on my car and directing it to the floor...

Tim

here's some info on the newer style idea of a catchcan IE the plastic ones you see now.

cooling

rad caps

[Bob Putnam]

Radiator caps that look like this



allow the system to suck back coolant from an overflow tank. Just remember to have the overflow draw from the bottom of the tank (where the coolant covers the intake )

We don't normally use an overflow in our systems - we are very careful to remove all the air from the system, and fill the expansion tank to about half-way.

[Frank Coppola]

Once again, this website proves to be the best tool in my garage.

Whaler, that website is great, thanks for the response.

Bob, I never realized there as a "second spring" in a rad cap. Very interesting.

Tovio and Zderf 1, Frank 0

Really guys, thanks for the input I find this stuff extremely interesting and greatly appreciate all your help.

[Zderf]

Bob,

For nearly 3 years now you have amazed and dazzled me with your knowledge and world assortment of images and graphics. Thanks for being part of this venue!!

Zderf

[excelguru]

What a website. I love this place.

I had one of those expansion tanks on my old Galaxy years ago. I couldn't even begin to remember where the overflow tubes went. I was too busy replacing leaked oil to notice the coolant.

So much information in one place... it almost seems wrong.

Keith

[Bob Putnam]

Not all caps have the return valve, so when you look for a new one check that it's got a brass "cap" in the middle. The spring is pretty light, so you should be able to get a fingernail under the edge and pull it up. Some look like they are right, but the brass is a big rivet to hold the bottom gasket.

BTW, I answered this question about 6 months ago and I never, ever throw away a graphic.