Need some help solving a coolant issue.


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I have a 2004 Jeep Wrangler unlimited. When I purchased it last year it had a bad heater core. I replaced the core and after a couple of days I was leaking fluid again. This time it was coming from the coolant lines that attach to the radiator. I tightened the hose claps and all was good for about 6 mounts. This time the top of the radiator was leaking. The P.O. had replaced this rad less than 5 years prior. I replaced the rad and again all was good for about 6 mounts. Now the heater core is leaking again. Any ideas about what keeps causing the failures in the coolant system? I use a premix universal antifreeze so no tap water or cross mixing types of antifreeze.

Strange.. I’m guessing your having no temperature issues until your major issues arise. Could be something in the system from somewhere else that is causing pressure to be high in certain areas. Have you checked thermostat and water pump? Or have you noticed anything in the coolant? Just throwing some thoughts out there.

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Are you seeing any white smoke on start up? If so, and even if not, you might have a head gasket leak or cracked cylinder head....sometimes these are hard to might remove the cap when cold and looking to see if you get any bubbles during idle.
That is odd that a new heater core leaks within a year.

What temperature do you normally run at?
How long does it take to get to that temp?
Are you overheating at all or prior to the leaking?
Are you finding you are low on coolant on a regular basis?
Does your expansion tank hold and keep fluid at the correct level?
With the new radiator did you get a new 18 lb cap?
Have you ever changed the thermostat? If so what temp brand and model?


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Never over heated. Runs around 220. Takes about 5 miles at highway speeds to warm up. With cap off cold and engine running there are no bubbles. When the thermostat opens the rad instantly starts to overflow. Expansion tanks holds when the system is not leaking, but I spring a leak about every 4-6 months with something new failing. Replaced the rad cap with oem cap when I installed the new rad
That is good. 220 few minutes to heat. Expansion tank holds fluid and no overheating.

Did you inspect the first heater core? Where did it leak? Was there signs or corrosion or rubbing...?

The radiator cap regulates pressure. If pressure goes high superheating and boiling can happen increasing pressure even more.

The two below charts describe a lot the first one shows ~65% coolant is optimal for max and min temperatures. However it doesn't show how water is a better heat conductor and absorbs heat with less coolant. So 50/50 is better for areas you dont get down to -30 or below.

The second is the triple point of water. I don't have one for a 50/50 mix. But the idea is the same. More temp, higher pressure until something gives or boiling occurs.

Most pressure test kits suggest not going over 18 psi I tested mine at 19.

Another thing I learned was the spring type hose clips expand with temp and will allow leaking at the hose clamp in place of erupting somewhere else. The stainless steel clamps do not release pressure. So despite how quirky they are the spring clamps serve two purposes.




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I didn’t see any apparent damage on the old core, but didn’t really check. I knew it was leaking from the steam coming from the vents. Once I removed the heater box it had antifreeze in the bottom to confirm the core was bad. I haven’t replaced this one yet. I would like to figure out what is creating the problem before I replace it.