I've been having problems with my 99 XJ overheating for a while now and can't seem to fix it! I replaced the radiator, thermostat, A/C fan, and the coolant. Both fans appear to work fine and coolant level is good. While the vehicle is running temp is at 220 but when I come to a red light temp drops quick. Then once I take of it goes back to 220 just as quick. Now I'm hearing a knocking noise from the engine compartment but only as it idles. Once I accelerate the noice goes away. Can someone help me out with this problem?

 

I am thinking you may have a bad fan clutch, Be real careful as far as overheat goes, From what I have heard with the 4.0 you do not want to let it over heat, As this could lead to cracking the head and you don't want that..

Im not one for throwing parts at a car /Jeep, but you may want to do the water pump while your at it.. Not hard to do and you will not have to worry bout cooling system for a while.. Mine as well keep all up to date...

Ant...

 

220 seems kinda high to me.. and usually they tend to heat up more while sitting idle if the clutch fan is bad, due to less air flow than when you're moving.. Yours sounds kinda backwards. Jeep temp gauges are not known for their accuracy.. When you say it overheats, does it blow out any coolant? Or are you just going by temp gauge needle? Maybe check the engine temp with one of those laser temp gauges? If it is for sure 'overheating', I'd check oil and coolant for signs of the two crossing paths, such as with a blown head gasket between cylinders. You can also check the spark plugs for contamination. Engines can make a knocking noise if they are getting really hot. But usually they'd be puking coolant by that time. Maybe the knocking is unrelated..

 

I think I will switch out the water pump as well while I'm replacing everything. Thanks

 

I was told by the sales person at autozone to try spinning the engine fan. If it automatically stops after I let go of it, then the fan clutch is good. I tryed it and it does stop. Is this an accurate way to check it? Spark plugs are new and no oil in the coolant not water in the oil. No coolant has blown out at all. Would it be better to get a seperate temp gauge? Thanks

 

Yea what Ant. said I would get a quality water pump. Otherwise don't want to be that guy but I would change your radiator cap. It might not be holding pressure can't hurt 10$ and a 30 second fix.

 

Sounds like a bad head or head gasket to me.

If it is the head gasket, it is blown between cylinders. Not into the water jacket.