98 TJ 4.0 cooling system overhaul failure

[Wakeangel]

I did the cooling system overhaul with all the recomended oem and Stant parts. Before the overhaul I did a Thermocure flush. When replacing the water pump and thermostat the engine block was squeaky clean. I decided to flush one more time with distilled water just for grins. Burped all air out. Levels were good, Temps have been running at a steady 203. Two days ago the jeep over heated and started blowing water out of the radiator drain petcock. The petcock seemed to shut ok and held. This morning it happened again. The only thing that hasn't been replaced yet is the heater core which is the original. Parts used: Mopar radiator and water pump, Stant 195 thermostat, Hayden fan clutch, distilled water and a couple of quarts of Zerex G05 after the first incident. I'm not sure what to do next. I'm assuming the petcock is bad at this point.

 

[pagrey]

Maybe the new cap is bad and isn't venting or isn't holding 18lbs? They are cheap and pretty easy to test as a first step. Unfortunately some new parts fail soon after installation, could be the thermostat too, anything you just put in.

(never heard of the drain blowing coolant either, as you suggested that's not normal)

 

[CharlesHS]

Does the radiator drain pet cock seal have debris under it or a nick in it ?
Might only show up under pressure.

 

[Wakeangel]

Does the radiator drain pet cock seal have debris under it or a nick in it ?
Might only show up under pressure.

I pulled it out to check for that. No signs of debris or damage. Right now it it's holding but if I turn it just a bit further it sort of pops back to open. The radiator cap is about a year old. It was working fine in the cheap aftermarket radiator I had till two weeks ago. But that'll be the next step after finding a new petcock. I'm guessing that's why it overheated. Pressure blew it out, but why? Everything was was great till that sudden failure.

 

[CharlesHS]

You need to determine whether the problem is with stripped threads on the radiator bung where the drain screws into or the threads on the drain valve.

 

[Wakeangel]

You need to determine whether the problem is with stripped threads on the radiator bung where the drain screws into or the threads on the drain valve.

I'll check that as soon as the new drain cock comes in.

 

[Wakeangel]

I found the problem. For anyone who might have the same issue. There's a plastic threaded insert that goes into the the radiator. The butterfly with rubber grommet then screws into it. The insert was broken. Probably from tightening it too much. Dorman makes a replacement part that seems to be thicker and heavier plastic. I had to file about millimeter of the radiator to get the new insert in place. You can see the crack in the mopar insert on the left. The dorman part on the right is shorter but that doesn't seem to effect performance. It tightened down properly and seems to be holding pressure. It's a little cooler than normal in the AZ currently but I'm sure we'll get some 110 and above degree days soon enough.

 

[NashvilleTJ]

Glad it was simple.

 

[Wakeangel]

Glad it was simple.

Same, it would've sucked to have to pull and ship back a brand new radiator that's getting increasingly difficult to find.