Coolant bottle overflow

Yesterday I drove my 1993 Jeep Cherokee which has the open system and antifreeze started pooring out of the coolant bottle overflow. It did it twice yesterday. It only does it when you turn your jeep off after driving it. I have all new hoses, replaced the antifreeze last year and have a new thermostat. I also flushed the radiator out last year. What could cause this to loose coolant?

Mine did the exact same thing about 3 months ago. After fighting with it for a week or two it finally ended up being a hole in the radiator. I was never able to see it because it was so small that coolant just evaporated as soon as it came out.

1993 Red XJ said:

Yesterday I drove my 1993 Jeep Cherokee which has the open system and antifreeze started pooring out of the coolant bottle overflow. It did it twice yesterday. It only does it when you turn your jeep off after driving it. I have all new hoses, replaced the antifreeze last year and have a new thermostat. I also flushed the radiator out last year. What could cause this to loose coolant?

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One of the more common reasons for this happening is air in the system. When you shut down a hot motor, the coolant will keep circulating somewhat (slowly) by convection. The pump may force enough coolant through an air block to work well enough, convection often doesn't. Hot spots in the motor boil some coolant and things spew.
Open system is better at moving air than the closed system, but far from perfect. Most common causes are it sucking air during the cool down cycle, when it recovers coolant from the recovery bottle. The hose from the recovery bottle has a crack or bad seal or there is a pinhole leak someplace in the coolant system. Sometimes pinhole leaks show up as a white spot near the seep. Two common but often overlooked spots are the water pump inlet clamp and under the fan shroud in the upper right hand corner (inside) of the radiator. Both spots will evaporate coolant rather quickly and sometimes never drip.
Don't overfill the recovery bottle, leave plenty of room for expansion. Watch the level change from a cold motor, to a hot motor. The level in the recovery bottle will usually go up an inch or more when started cold and run to operating temperature. And then the level will go back down after the motor is shut off and cools back down to ambient (this usually takes awhile).
I marked the recovery bottle in the wifes 96 with a black marker. a line at full cold and another at full hot. I can tell at a glance hot or cold if there is any coolant missing. The add and full marks aren't real helpful in keeping track of the coolant level on a regular basis.

You say it only does it when you turn it off after driving it - did you see coolant coming out of the bottle or did you just see a puddle on the ground? The reason I'm asking is because a water pump that's about to fail will leave a puddle after you turn it off.

If you did see it come out of the bottle, what was your temp gage doing? Did it show it overheating while driving? Did the temp increase after you turned it off?

Too full to start with?

I watched it coming out of the overflow bottle. I'm not sure how much coolant was in the overflow bottle before the overflow. I have never had this problem before and I haven't touch the overflow bottle for months. I have the dumby gauges and have no idea what the temperature was. My light never came on. I replaced my radiator cap today. I went on a short drive today and no problems. Tomorrow I'm going on a long highway drive and we will see what happens.

When the engine warms up the coolant expands and goes into the overflow, when the engine cools back down, the coolant goes back.

Any small leak and it don't go back, next time the engine gets hot more coolant comes out and can overflow.

What is the correct PSI on the radiator cap. Napa and Autozone has 13 psi on the computer. I went to the dealer and they didn't have a cap but he thought it was 15 or 16 PSI. Mine had 16 PSI cap on it so I bought another one from Autozone a 16PSI just like the one that was on there.

Make sure your not running straight antifreeze either, i know thats dumb but when i first started having probs, i was pouring in straight Antifreeze. Also you dont need a full bottle either. but it sounds like its your cap. ive been through 4 caps and this one is holding up pretty well (knock on wood)

Stock is 13 #

No I am not running straight antifreeze. I am running 50/50. Will it matter if I am running a 16 PSI cap instead of an 13 PSI cap?

No big difference, though the recommended part is usually the better choice. If the cap wasn't holding preessure and it was pushing coolant into the recovery bottle, most likely it would be worse while driving. You'd likely leave a trail of coolant.
Bur heck a new cap is always a good idea and may be the cause.
Or part of the cause anyway. I had multiple things going on in my wifes 96. Radiator was partially plugged, the radiator had a pin hole leak and the cap spring was weak. Took me a few tries to work all the bugs out. Sometimes it adds up and isn't just one thing.