Difference between catch can and recirculating catch can?

[Mike kZ]

I know the difference, one catches the overflow, the other recirculates the fluid back into the radiator. But how do they differ internally? What makes the recirculating one suck the fluid back in the rad, but I assume the overflow can does not do this.

[Pop N Wood]

My guess? The radiator overflow can has a tube running down to the bottom. Thus when the radiator/engine cools, the fluid in it contracts. This causes a vacuum which sucks the fluid back from the overflow, just like a straw.

 

A catch can, I would assume, just has a connection at the top that dumps the fluid into the top of the can. Any vacuum on the inlet line will only vent air through the can.

[Mike kZ]

That makes sence, so all you have to do to a catch can is run a hose inside to the bottom.How about running the hose from the rad to the bottom of a catch can, wouldn't that work too?

[Pop N Wood]

Yes, but then wouldn't you have a recirculating catch can?

 

I don't know of any other systems that would be recirculating besides the radiator. The radiator is a totally sealed system that is filled completely full of fluid (no air bubble). Everything else (oil, fuel, whatelse?) is vented to atmosphere. I think some race rules require anything that can spill on the track to be vented to a catch can. In that case you definitely would not want a recirculating can.

[Scottie-GNZ]

Mike,

 

I have been using the stock Z bottle for quite some time and have no problem getting through tech.

 

[Mike kZ]

Originally posted by Jim Powers:

Yes, but then wouldn't you have a recirculating catch can?

 

I think some race rules require anything that can spill on the track to be vented to a catch can. In that case you definitely would not want a recirculating can.

Why wouldn't you want a recirculating can? A regular catch can catches the overflow, but then you have to either drain and return to the rad or throw it out. A recirculating catch can will suck the overflow back into the rad, no?

[Pop N Wood]

You misunderstood me. Definitely want a recirculating overflow bottle on the radiator. Otherwise you lose cooling capacity when air instead of water is sucked back into the radiator.

 

But if you vent oil or fuel to the can, then you don't want any of that going into the radiator. So a recirculating can for the radiator, and a simple catch can for everything else.

[Tim240z]

As I understand it:

A regular catch can will allow air to be sucked back to the rad.

When the radiator is hot and the liquid expands to create pressure, the overpressure (more than what the rad. cap is rated to) will bleed into the catch can. As the radiator cools (engine off), a vaccuum is created by the decreased volume of the colder water (&coolant). If the tube going from the rad. to the catch can is immersed in liquid, then it will draw in liquid (to the rad.), if it ends at the top of the catch can (in air) then it will draw in air.

HTH.

Tim

[nullbound]

yup. my stock datsun overflow bottle works great. when the radiator cools down, coolant is sucked back into via the vaccuum effect described in previous posts.

[Mike kZ]

Thanks guys, My car didn't come with a stock overfow can. Does anyone have a spare?

[jt1]

I use one of the generic plastic catch cans from Doug Herbert performance. It has rubber-grommented inlets on the top and bottom, and comes with a small valve. To use it as a catch can, you run the overflow into the top and dump it with the valve. I run the overflow into the bottom, put the valve on top and leave it open. When the radiator pushes fluid into the can, it sucks it back when it cools. Works great.

www.herbertperformance.com, or I think Summit sells a similar one.

[Pop N Wood]

My radiator overflow bottle is a sports drink bottle connected to the side of the radiator with a large hose clamp. Got the bottle free as a promotional give away from a local radio station. Just pull out the straw an run in the overflow tube.

[TomoHawk]

Remember, you need a special kind of radiator cap to use the "coolant overflow container" (what the OEM guys call it,) probably a certain kind of radiator too. I would think that you can get one from an auto part store or radiator shop.

In fact, i think mine had one because the tube is there with the cap, but the can is missing! I hope that it hasn't been spilling coolant out on the street! I better check it when I get it back from the Trans shop.