Is the Coolant Tank Pressurized?

[seedpress]

Does anyone know whether the coolant reservior (overflow tank) is pressurized or not? In other words, does it vent to ambient air pressure, or is it sealed up to some pressure point? I have an '90 Bronco 4X4 with the 5.8 liter engine, Eddir Bauer Edition; however, I think a broad range of years and models use the same overflow tank.

The reason for this question stems from a coolant leak that keeps appearing on the fender underneath the coolant tank. I can feel the coolant dripping from the bottom of the tank after the engine has been running a while. I'm pretty sure it hasn't been coming from the hose and ******. (Earlier, I had a problem with it sloshing occasionally from the refill cap. The cap had become loose. So I fixed that.)

In an effort to find the new leak, I removed the tank and submerged it in some water. The refill cap was oriented at the bottom of the water, and the hose ****** at the top. When air pressure was appled through the hose connection, then, sure enough, bubbles came out of an area pictured here:



Note the messy hot glue I've added to the area that was formerly "leaking" air. This was done in haste -- after I saw the air bubbles. Now nothing leaks, but it has since occurred to me that perhaps the "patched" area is actually supposed to let air out. Hence my question about the pressure.

The tank seems to be made of polyethylene, which is difficult if not impossible to glue. Nevertheless, the hot glue that was used to plug the air "leak" seems to be adherring -- for the time being. But I could probably peel it back off, if it turns out that I shouldn't have plugged that area. Then I'll still be left with a leak. And after the area pictured was sealed, there were no more air leaks, so I am assuming the coolant drip was somehow coming from that area, though it's at the top of the tank, and I haven't overfilled the tank.

Anyway, is that tank supposed to be pressurized or breathable?

 

[miesk5]

yo SP,

the Coolant Recovery Tank is Not pressurized in our Broncos.

Some later years did get a Degas system

Overview; "...As with virtually every substance, coolant (and any trapped air) expands as it is heated by the engine. Up to a limit, this effect is utilized to create the pressure which increases the boiling point. But excess pressure must be vented, without releasing poisonous coolant onto the ground. So a pressure cap is used either on the radiator for a system with a vented overflow tank, or on the "degas bottle" for a fully-pressurized system. The cap has 3 main functions: a) to seal the pressurized portion of the coolant system up to the target pressure; B) to direct the UNpressurized portion of the vented system into the overflow tank; & c) to allow coolant to return from the unpressurized tank into the pressurized system when the system develops a vacuum (during cooldown). This return of vented coolant is dependent on the radiator hoses being fairly rigid, either because of their rubber compounds being stiff, or because of internal springs which support their shape. Hoses that are too soft (often due to oil contamination or just age) will simply collapse, preventing the return of lost coolant from the unpressurized overflow tank. This is just one reason for the increasing use of a pressurized tank (degas bottle) which is designed to hold a specific air pocket within the pressurized system. The air creates a spring that allows for coolant expansion without the risk of coolant loss due to venting; even to an overflow tank. Both systems ultimately allow failsafe venting to the ground.."

Source: by Steve83 (Steve, That dirty old truck)

The tanks are prone to leaking like that or seeping dribbles out @ cap area; I use a thin alum foil section, rolled up lengthwise to use as a gasket to keep it from seeping out too much.

see what type of material recycling class is stamped on the tank to figure the best sealant to use on it.