04 jeep liberty 3.7. cooling resevoir boiling and overflowing out the back

could have a bad thermostat or bad head gasket.

Thanks I replaced thermostat still doing all signs pointing to head gasket removed cap and and started overflowing out where the cap goes

You can do a combustion leak test to be sure, test kit cost about 40 bucks and lots of YouTube vids on how to do it. Fairly easy and quite conclusive.

Did someone paint the nose on your Jeep and fail to mask off the a/c condenser cooling fins. Air must flow across them. Make sure the cooling fan is there - And that there is a breeze of air across the engine at idle in your driveway. Put your hand - where you can feel the air flow. If you have gone mud riding - Make sure that there is not mud packed between the cats and the engine or oil pan. I have seen synthetic oil become ruined because of this kind of heat transfer. And last - It is possible on this engine - To have a vacumn leak - And cause the honey comb in one cat or both to heat sear and ruin. Raise the vehicle on a lift - Ask your mechanic to use an infrared heat gun and Test the head pipes, Test the cats. And check after the cat - For high temperature soak, I had that to happen on ours. Had to replace the left side cat.