Coolant Reservoir Empties, but Radiator Always Full

[MattEnTheHat]

Edit: I seem to have found the source of the problem, see my reply below for details.

So my coolant reservoir empties out fairly quickly - if I top it off when I get gas, by the next time I fill up, it will have dropped maybe halfway, and continues to drop until it is completely empty. The radiator, however, is always completely full, and stays that way even if I drive with the reservoir empty. Temps seem fine - they got rather high once while wheeling in 100°+ weather (lots of idling and very slow driving at high-ish RPM), but other than that no issues.

Just did one of those tests to check for exhaust gasses in the coolant, and it came back negative, and both the coolant and oil look clean. I can't find any obvious leaks, or puddles when I park.

Seems like the simplest answer is just that the reservoir itself has a slow leak, but since I haven't been able to actually find one, I'm not sure.

My thoughts for next steps are:

• Cooling system pressure test (but pretty sure this will be OK, since the radiator is always full?)
• UV leak locator test - maybe I'll be able to find the leak that way?

Any other suggestions? Is this even something I should be worried about to begin with?

 

[MattEnTheHat]

Whelp, it seems I've answered my own question. Pressure tested the cooling system, and there is most definitely a fairly significant leak. Its in the hose pictured, near the bottom (kind of out of sight in the picture) - looks like this hose leads to the radiator core. I'll update with info on whether this fully resolves the problem once I get a chance to replace it.

Still not sure why the level in the radiator never seemed to go down... I guess maybe I just never drove it for long enough before topping up the reservoir?

 

[Jen1999]

I hope that fixed your problem! Fluid issues are a pain to deal with!