I've been trying to figure out this coolant leak for a while now but havent had time to tear the top support off.

It seems to leak solely around the neck of the upper rad hose. I replaced the hose and it's secure. The "old" hose showed no sign of wear, cracks / splits or otherwise.

Could the stock upper radiator neck be warped? It's original (2000 Jeep XJ - 197k). It only seems to spew when the AC is on but it doesn't ever over heat. It may climb up at a long red light but the electric fan kicks the temp back down no problem.

Despite it leaking enough to form a small puddle here and there, before work (when it's cold to ambient temp over night) I'd pop the radiator cap and it's still has coolant topped off. Is it over filled? Is such a thing possible? I don't think there is much if any air in the system.

Am I just due for a new radiator?

 

I had similar symptoms right before my XJ overheated and my radiator exploded wile I was driving it (leaking radiator and engine heat climbing wile I was stopped at idle). When I got in there I found that my thermostat was stuck shut. I wound up having to do a t-stat, radiator and a water pump before it was all said and done and I wasn't leaking coolant anymore. I would nip that in the butt and at least do a t-stat and radiator before you have a breakdown.

 

The upper rad hose gets rock hard some times. What causes this pressure? It's probably so high it squirts out the neck/rad hose connection. I replaced the Tstat twice since owning it (little over a year).

I will go with a Mopar Tstat this time instead of regular pep boys. From photos the mopar one has a steam vent hole. The problem started happening about 2-3 weeks ago. I drove the XJ from Philly to Virginia and back this weekend. No leaks to and from. But when I get back home. It spews a puddle when I take a 5-10 min drive in the city with aC on

 

I really have no idea how having the A/C on would affect the cooling system. A pressure build up in the upper rad hose is a symptom of a stuck t-stat though.

 

The only thing I can think of is that the AC condenser gets hot, increasing the temperature of the air going into the radiator. That might push a marginal cooling system over the edge.

 

I tried my usual "go to work and come back" trip minus turning the AC on. It's almost 80F today. The temp in stop light to stop light was 209 to about 213. No spewing coolant but he upper rad hose was pretty hard coming home. The new Tstat and gasket is already shipped.

I just won't use the AC, thankfully it's nearly winter. Then once I get some spare cash and time I will upgrade the Rad. I am looking at a champion 2 core. With shipping it comes to about 185$.

Any recommendations? I have a ZJ fan clutch so 2 core is probably the biggest I can fit.

 

Scratch that, I got back out to run a quick errand and there is the slightest of drips that occurred after shutting down. Probably heated up and built pressure. Hopefully the new Tstat fixes this. It isn't nearly as bad as when the AC was on and you could see it running down.

 

I used all NAPA parts (radiator, t-stat, water pump and hoses). Everything is holding up fine so far and my temperature stays pegged at just under 210 degrees and doesn't move at all. Good luck.

 

AC on causes engine to work harder.

Harder working engine gets hotter.

Hotter water can build up pressure, making hoses hard.

Does not mean T-Stat is problem ...... just excessive heat build up.

If T-Stat is stuck closed, you will overheat and boil over ..... you do not want that.

If you flip the lever atop the radiator cap this allows pressure and excess coolant to bleed back into reservoir.

IF running the AC is causing this, I would make damn sure the second fan ( the electric one ) is coming on when you turn on the AC.