Radiator Overflow

[nivensid]

1896 CJ7 L6 T-5 Transmission . Currently my temp gauge is not working but i have a mechanical gauge to install when i can find the time. The engine runs good and have not noticed any overheating issues. I took off the radiator cap the other day and the coolant appeared to be low. I could only see the cooling fins and no coolant so i topped it off, took about quart. The overflow was dry so i filled it to the cold full mark. Went for a drive and the radiator was leaking at the cap when the engine was cut off. It continued to leak until the level was back where it was in the beginning. The overflow never changed levels. I can drive with it at this level but shouldnt the coolant level be visible when the cap is removed?

 

[Torxhead]

When the radiator cap is removed the coolant level should be all the way to the top. Coolant expands when it gets hot moving it into the recovery bottle.

 

[nivensid]

When the radiator cap is removed the coolant level should be all the way to the top. Coolant expands when it gets hot moving it into the recovery bottle.

That's what i am tryig to figure out, why its leaking under pressure at the cap and not flowing to the overflow? Guess i will try new radiator cap.

 

[Torxhead]

The coolant is supposed to flow thru the outlet hose on top of the radiator into the recovery tank. So either you have a bad radiator cap or a bad radiator filler neck.

 

[mtnwhlr]

I would think your cap is bad.

 

[Lumpy Grits]

Get a new cap and not the lever pressure relief type(they all seem to leak after a time).
All you need is 12-14psi cap.
LG

 

[BusaDave9]

I think you already got your answer but I think this picture might help explain.

As your engine gets hot the pressure of the coolant overpowers the main seal (yellow). Then coolant gets past the main seal and has one of 2 paths. It can go out the overflow on the right or it can go past the upper spring seal (purple line). It should go out the overflow hose unless the upper spring seal is bad.
You need a new radiator cap.

One other possibility is the overflow hose is blocked or kinked.

 

[Hedgehog]

The question for me is, why isn't the over flow going into the over flow container? I'd check the tubing going from the radiator/cap to the container. Can you blow air through the hose? Is the hose in the container going all the way to the bottom or is there a drain at the bottom. Something seems to be plugged. .... Oh yeah, I agree with getting a new cap. They don't last for ever.

Water doesn't really expand when it's hot unless it turns into steam. The following is from an internet search:

"Normally, things expand when heated and contract when cooled. Water is an exception to this rule. Even though water does expand when heated and contract when cooled at most temperatures, water expands when cooled and contracts when heated between 4 degrees Celsius and 0 degrees Celsius."

Yes, I know, from what I've seen it doesn't make total sense to me either.

 

[nivensid]

I think you already got your answer but I think this picture might help explain.

As your engine gets hot the pressure of the coolant overpowers the main seal (yellow). Then coolant gets past the main seal and has one of 2 paths. It can go out the overflow on the right or it can go past the upper spring seal (purple line). It should go out the overflow hose unless the upper spring seal is bad.
You need a new radiator cap.

One other possibility is the overflow hose is blocked or kinked.

Thanks for the pic, helps explains how it works