Overflow tank

[stallion112]

I recently replaced my plastic overflow tank with an aluminum one that is equipt with an opening for a radiator cap.

My question is that since the plastic tank had a "snap on" style cap vented to the atmosphere, can I tighten the radiator cap on the new tank or do I need to leave it loose and vented to the atmosphere as well?

[wizard]

Loose.
If it's tight pressure will build and prevent water from moving back and forth.

An alternative you might try is use a radiator cap rated at less pressure than your regular cap, the lower the better, but I would still be careful.

How is water routed to this tank? Normally , they are fed from the bottom so water moves back and forth and not air. ( am assuming you have a hose connected at the other end to the pressure bleed off port on the primary filler neck.)
Some pics would helpful.

[ByronRACE]

If you're using this tank as a recirculating catch-can, the can should be vented to atmosphere, and the fluid needs to enter and exit the can as the liquid in your cooling system expands and contracts. So, you need a siphon tube going to the bottom of the tank, or you need to connect your overflow line to the tank bottom. As the fluid expands, it'll fill the tank. As it contracts, the vacuum of the closed system will draw the fluid back in.

If you're using the can purely as overflow, then just vent it to atmosphere and pour the fluid in the top without a siphon tube. I don't recommend this. A recirculating overflow as described above is more useful.

By the way, do you need a set of manuals for your Stallion? I have a 1982 car (West Coast) and have scanned a full set of stallion/west coast manuals to PDF. If you need them, I can make them available for download. They detail everything and show the root source of the parts that comprise the car.

[wizard]

Good advice Byron - I'm almost done replumbing mine. It took a while to find the right tank. Will give you an update soon. (It's the cooling issue we discuss earlier in the year, if you remember)
I would be interested in the PDF you mentioned.

Stallion, we'll get you fixed up, I'm sure.

[stallion112]

Byron,
I guess I used the wrong terminology. I am using it as a recirculating catch can and not an overflow tank. I have it plumbed from the expansion tank to the bottom of the recirculating catch can and will use it as you described where the fluid can expand and contract. I have a 13# cap on the expansion tank and a 7# cap on the recirculating catch tank. I planned on keeping the 7# cap loose.
Thanks for the offer for the pdf file of the owners manual. I downloaded the file from you a few months ago. It happened to be the same as the one I have that came with the car. It's pretty beat so your scanned copy will be helpful.

Wizard,
Thanks for your advice, too. Looks like I was thinking along the same lines with the low cap rating on the catch can. I'll report back once I have a chance to get the beast started.

[ByronRACE]

If you're trying to vent the tank to atmosphere and it doesn't have a vent, you could always drill a small hole in the cap. Caps are relatively cheap. Might be more reliable than a loose cap.

I'm using a $13 summit overflow can (plastic) mounted behind the passengers headlight. It comes with a top fitting, bottom petcock, and is ventilated to atmosphere. The only mod was to pull off the top fitting and add a siphon tube to the bottom of the tank. Heater hose runs to my filler neck, which is a gessford filler/thermostat housing that places the fill point very high. I also do not run an expansion tank. This has proven to be a trouble free solution.

But, it certainly doesn't give you the appearance of vintage-correctness by any means. I'm not into that. My powertrain is the sort of thing that gives true vintage-correct restoration people nightmares. LOL