Overflow bottle/cooling system design help, please.

89 4.0 XJ
I have done the cnversion to convert my closed system into an open by installing the Moroso Filler neck into the upper radiator hose. The problem is over a period of time I loose a pretty good amount of coolant and the Jeep starts to overheat(obviosly). I belive most of the coolant is leaking out through my expansion/reserve tank and am looking at how I might fix this.

I have the filer neck in the upper radiator hose. The small overflow hose runs from the neck to the stock pressure tank. The inlet on the bottom is where the coolant come sin at and the upper outlet is the overflow hose. Does this sound like the correct setup? I am thinking of running the overflow hose to the bottom of the tank so it would take some pressure before the coolant would overflow, would this help at all? Any insight would be appricated.

Should the expansion tank be below the radiator fill neck? May have solved my own problem. Also is the any diffrence is how these two tanks should work. What I eman is the inlet coming from the bottom of the overflow tank or coming through the top and ending towards the bottom of the container as showen in the two pics.

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I did a bed mount radiator awhile back, found after some trial and error, that the full line (hot), on the recovery tank should be level with the top of the radiator (or highest point in the cooling system). Or in other words the highest coolant level in the system, should be pretty close to the full point on the recovery bottle. I guess theoretically it shouldn´t make much difference, just seemed to work the best that way.
Be sure an allow room for expansion, in the recovery tank.
I just went out an measured, the filler cap for the recovery tank (on my 95 XJ) is two inches higher than the radiator cap.
I measured my bed mount radiator, and I eneded up with filler cap (for the recovery bottle) being about 2 1/2-3 inches, above the top of the radiator.
Don´t think it is an accident Jeep and I ended up, with about the same set up.

I´ve had trouble in the past, got to remember the cooling system goes into vacumn when the motor cools down, a little coolant out a little air in, it adds up after awhile. Just a possibilty.

Weasel said:

I have the filer neck in the upper radiator hose. The small overflow hose runs from the neck to the stock pressure tank. The inlet on the bottom is where the coolant come sin at and the upper outlet is the overflow hose. Does this sound like the correct setup? I am thinking of running the overflow hose to the bottom of the tank so it would take some pressure before the coolant would overflow, would this help at all? Any insight would be appricated.

Click to expand...

Definitely not.

It sounds like you kept the plastic bottle as part of the system. That means it still needs to operate under pressure. However, the small overflow tube from the new filler neck does NOT operate at pressure, because it connects outside of the pressure cap. You need to either bypass the original plastic bottle, or else reconnect it the way it was and add an overflow recovery bottle to catch the overflow from the new neck and let it flow back into the system when the system cools down.

Just another thought I had, you got to be carefull what kind of cap you have. An old type radiator cap (before recovery systems) lets fluid out but only works, in one direction, totaly open system, lets excess coolant vent out onto the ground.
A recovery system cap, lets the coolant out into a recovery tank (above say 12 PSI) and when the motor cools down and the system goes into vacumn, it sucks some of the fluid back out of the recovery bottle into the cooling system.
Surge tank (closed system) allows enough space in the surge tank, to deal with most of the expansion. Guess the closed system cap vents also, but is only supposed to vent air.

Eagle said:

Definitely not.

It sounds like you kept the plastic bottle as part of the system. That means it still needs to operate under pressure. However, the small overflow tube from the new filler neck does NOT operate at pressure, because it connects outside of the pressure cap. You need to either bypass the original plastic bottle, or else reconnect it the way it was and add an overflow recovery bottle to catch the overflow from the new neck and let it flow back into the system when the system cools down.

Click to expand...

I did retain to stock bottle but only to use it as the recovery tank. The filler neck I installed has a pressure cap on it which is before the smaller runoff tube from the filler neck. Being in the stock position I would suppose it's three to four inches higher then the filler point.

Weasel said:

I did retain to stock bottle but only to use it as the recovery tank. The filler neck I installed has a pressure cap on it which is before the smaller runoff tube from the filler neck. Being in the stock position I would suppose it's three to four inches higher then the filler point.

Click to expand...

So what did you do with the bottom inlet on the stock bottle? From your original description it sounds like that's still connected to the system. With an "open" system, nothing in/on the recovery bottle connects to the pressurized side of the radiator cap. There should be one line from the filler neck vent to the catch bottle, and the catch bottle also has a vent to atmosphere.

Where you may be screwed up is that the tube inside the catch bottle has to be below the level of the coolant so it can siphon back to the radiator as the system cools off. I don't see any way you can do this with the stock bottle.

I made the stock bottle into the recovery/catch can. The bottom inlet on the bottle is where the overflow line from the filler neck hooks up, so the fluid comes in the bottom and should be able to be siphoned out the bottom as the system cools. The upper inlet on the bottle is the overflow tube that alows fluid to escape if system pushes too much coolant into the bottle. I'll try to get a pic of the system tonight that may help illustrate the system better.

Okay, that should work. Are you certain it's the bottle where the coolant is being lost? Could the water pump or lower radiator hose be weeping? Heater core okay?

How full do you fill the bottle? In original configuration it should be half full when cold. I'd gues that's probably a safe starting point for your modified system. If you fill it too full when cold, you're going to lose some.

How has the weather been where you are? One of the reasons I don't like the conversion you did is that you lose system capacity. The Moroso surge tank that I used costs a bunch more, but it holds more than the original bottle so I have increased the capacity of my cooling system at the same time I eliminated that pesky plastic "thing." Maybe you're just dealing with a marginal capacity?

Heater core was replaced last year. No smell of leaking. I check the gorund after I park and see no signs of loss of coolant on the undeside or ground. No bubbles form the system when running with the cap off that would indicate a head gasket. The only thing I can think of is that when the bottle fills up the fluid sloshes around and leaks out the overflow tube and when the system cools it suck less fluid in each time.

And about half full is where I fill it. It takes about three to four weeks for anything to show up temp wise, but it takes about .5-.75 of a gallon to fill it back up.