[hawkens1024]

I’ve been battling a cooling system issue where coolant gets pushed into the overflow tank but doesn’t always return after cooldown. Jeep doesn’t overheat. Here’s what I’ve done so far:

• ✅ Replaced radiator (new)
• ✅ Replaced water pump, thermostat, and temp sensor
• ✅ Verified no overheating — coolant hits ~224°F max
• ✅ Fan kicks on late (around 223–224°F);
• ✅ Radiator cap replaced with Mopar 4596198 and Stant 10234 — no change
• ✅ Overflow hose replaced
• ✅ Burped the system multiple times (nose uphill, cap off, watched bubbles)
• ✅ Block test with Gold Label kit — no color change
• ✅ No white smoke, oil is clean, system passes pressure test

 

[Digger84]

is the overflow hose tight fitting as any small air leak and it will suck air not coolant as it cools

can even put clamps over each end of hose

 

[hawkens1024]

is the overflow hose tight fitting as any small air leak and it will suck air not coolant as it cools

can even put clamps over each end of hose

Yes, it is brand new

 

[Jeepwalker1]

The big question is "Why" does the coolant get pushed into the overflow tank in the first place? How are you measuring temps? Have you verified the engine operating temps with like an IR temp gun at the metal water outlet?

Do you hear any 'gurgling' at the heater core in the morning after you start the vehicle...and go to accelerate to drive it away?

Is there excess pressure on the radiator hoses?

Is there any milky substance (Ever) on the underside of your engine's oil filler cap?

Is there any vacuum on the cooling system during the cool-down stage? You can often hear it sucking back fluid ...do you hear any of those sounds? What if you were to undo the radiator cap on the cool down stage ...do you hear a 'sucking' sound? If so, might be a bad radiator cap.

Is your radiator cap Mopar or aftermarket?

It could be something else going on... like head gasket. But get answers to the above questions first.