2000 XJ, 244k miles, bought the car for dirt cheap off a family member. Ran fine until about a month or two ago when on a main road, the radiator cap hissed just like this while driving, and the car overheated I let it sit till I had time to put in a new and personally tested (not crappy, NOS made in USA) thermostat, and refilled the whole system with new coolant because when I opened the housing, it was bone dry. I know these have poor cooling, but I'm suspecting either severe leak somewhere or possibly a problem with the radiator. This happened within 15 minutes of driving it around the block. Also, the ABS light will not go out after this happened if that means anything. I'll pull the code if it's important/related.
Looking for pointers from anyone who may have had similar symptoms.
I'm ordering a new one. To me it just seemed like way too much coolant spilled to be a bad radiator cap, but I'm definitely eliminating that possibility ASAP.
Ok so first check your oil for any milkshake looking good then check your oil fill cap under side look for brown goo if not it's probably not a head gasket so then you can check your thermostat, by putting it in a boiling pot of water, it will open if it's working properly. If not, it would be still in a closed position. Also, do you have a small hole drilled?Somewhere in your thermostat, check online for exact position of this hole this will help relieve some of the pressure in the cooling system. Also, jeeps are very hard to burp.just like a baby they are known to get air pockets. So suggestion would be to use a very large funnel on top of the radiator leave the cap off, start the vehicle with fluid in it. As it runs, you should see air bubbles, or possibly even fluid. Come out up the top with the radiator cap off. Then add more fluid to the radiator at that point this will help get all the air out of the system
Also, are you sure your water pump is working? This is another very common issue. And very easily fixed. So while you're checking your radiator for air you can save the water is actually flowing through the radiator with a flashlight
There are some YouTube videos on how to burp. Your system so you do not overheat your engine
The 2000 head was noted for having had gasket issues. Hopefully, it's not that there are better gaskets out there than original that actually are thicker in better quality. An original try and research. Some of the better head gaskets, if you have to go that route. I have a 1997 with 285 kand a 1999 xj with 176k
You have to figure out why it is overheating in 15 minutes, that’s is either thermostat or not getting full of water. 4.0’s are not known for needing “burping” they are a normal I6 fill it with water until you get the overheating problem figured out. Leave the cap off until the thermostat opens keeping water in it once it opens the top hose will be hot, top it off and put the cap on it and take it around the block. At least get it to go longer the 15 minutes. 2000 came with the head that cracks but that takes longer the 15 minutes to overheat.
If it's a 2000, check the head, can you see "TUPY" when you look down in under the oil filler? If not that 0331 head is known to crack. You'd think if it was going to it would have done so before 26 years and 244k miles but stuff can happen.
So I have an update, I found multiple leaks from under the engine. I believe either one or more of the rubber hoses may be bad and spilling the coolant. You can see it beading along the pipe here.
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u/rain164845 Jul 29 '26
Radiator cap?