I just installed a new radiator in my Cherokee yesterday and put it on some front wheel ramps to “burp” the system to get the air out when I refilled it. The radiator overflowed a bunch. I added more water then took it out to see what the gauge would read. It started to overheat and then pegged the red. We let it cool off with the application of water to the outside of the radiator and limped home. I ordered a funnel gizmo from Amazon that was made for filling radiators last night and it arrived today. I put it on the radiator with the Cherokee on the ramps. The funnel after the Cherokee warmed up a bit overflowed a lot. The hose from the thermostat housing to the top of the radiator was not hot. The thermostat housing was hot
Is this a thermostat issue?
Thanks for your knowledge

 

Sounds like the thermostat might be stuck closed, so coolant isn't circulating.

 

Did the thermostat have a bleed hole or did you add one? The bleed hole really helps getting all the air burped out. If you just fill it cold and run it, you'll be very low on coolant and overheat very quickly.

 

I am not sure if I drilled a bleed hole in the thermostat when I changed it out a few years ago. I am going to get a new thermostat tomorrow and will replace the old one. We will see if I did drill a hole in it. I will let you know. NAPA opens at 9:00 tomorrow morning.

 

Alright, I installed a new thermostat a 195° one. I still had a problem with the Jeep wanting to overheat. The funnel gizmo I had wanted to overflow. My next thought is possibly the water pump is shot. I had replaced it about five years ago when I first got the Jeep, along with a new radiator and a new thermostat, hoses, fan clutch. The thermostat I put in I tested in hot water, it opened around 200 instead of 195. About how long do the water pumps last?

 

Are when it cools off, are both the radiator and the overflow tank full to where they should be?

I did the same install(s) on mine about 5 years ago too. Not sure how long the replacement ones last these days... but the parts are still relatively affordable... so cheap insurance and a pretty easy job to do yourself.
Just about to order the parts to do mine again just to be safe... I've been in the south with the XJ for about 5 years now so figure can't hurt.

Make sure you have the orientation of the bypass hole in the thermostat correct and the thermostat itself is oriented and seated correctly. Never hurts to double check... the old "measure twice cut once" rule. It can happen to anyone.
when the t-stat opened in your hot water test... did it completely open?

 

Sounds like a stuck thermostat. If the upper radiator hose isn’t getting hot but the thermostat housing is, the thermostat isn’t opening. Replace the thermostat (get a quality one, like Mopar or Stant) and try burping it again with your new funnel. Also, check for leaks and make sure your electric fan is kicking on.

 

How totally embarrassing! After changing out my radiator, still overheating, and then the thermostat. Still overheating 🥵 I had purchased a new water pump to install. Before I started the task I thought let’s just look at the top radiator hose that is not warming up very well. Indeed, the rubber cap that covered the inlet of the new radiator was in the hose blocking water flow. It was removed and the water temperature was fine. Wonder how that cap got in there?

 

lol.....well, at least you shouldn't have to revisit your cooling system for a bunch of years.

 

If life as a mechanic working on older and classic cars has taught me one thing it is that it is good to look for why a part failed before just replacing it. Glad to know you’re back on the road again.

 

That's funny. Glad you caught it. That would have been hard to find because no-one would suspect a big 2" radiator hose to be blocked off inside.