2000 2wd Cherokee Sport 6cy. All stock, 100k miles, runs great, clean oil. Mostly around town use short with limited highway trips. Started overheating and boiling over spewing out radiator cap on shut down. Flushed (lots of rust and grime,) replaced thermostat and radiator cap and fresh coolant. No more overheating, solid at 210˚on the gauge. Now occasionally spewing out radiator cap a bunch of coolant on startup. Sometimes also on shut down. Not leaking while driving or idling warmed up. What next? Clogged radiator? Water pump? Perplexed. Any advice appreciated! Thanks!

 

You have a 2000 so it's possible that the head is cracked and hot exhaust gas is getting into the cooling system causing the overheating and spewing of coolant from the pressure. You need to do more checking. I doubt a water pump or clogged radiator could do that.

 

It shows none of the usual symptoms like water in oil or steam in exhaust, rough running/misfire, etc. Also, does not overheat since thermostat (definitely faulty) was replaced. The spew is on cold startup and sometimes but not always on hot but not overheated shut down. Are cracked heads common to 2000 models? Where do they usually crack? Is it repairable or require a new head? If a new head, what is best year or source? Are head gasket issues common? Thanks Again and apologies for all the questions!

 

The 0331 head on the 2000-2001s 4.0 crack between the 3rd and 4th cylinder most commonly. If these year engines overheat it is very likely that the head cracked. I would buy a new head if that's the problem. Just Google it.

 

Compression and/or leak down test.

 

Check neck of rad yet where cap seals ? Did you pressure check new cap ?

 

You can rule out exhaust gas in the coolant using a tester like this one:



Or this one, which is a little better but more expensive.



Many mechanics have these and can test it for you if you don't want to buy one yourself. It will tell you pretty quickly if you have exhaust gas escaping through a head crack or leaking head gasket.

What strength radiator cap did you install? If the combustion leak test is okay, you might try running a 16 lb. cap. Stant or Carquest brand is preferable.

Also, you can't be sure you don't have coolant in your oil just by looking at it. The detergent packages in modern oils do not let the oil turn cloudy like it used to. The best way to rule out coolant in your oil is to send a sample off to a lab like Blackstone for analysis. It's $25, and they'll send you the sample collection kit for free.

With the 2000, you need to take any cooling issues very seriously. Don't let it go. If your 0331 has cracked, you need to swap it as soon as possible to avoid bearing damage. Otherwise you're swapping the whole engine instead. You can get a complete, ready to drop in replacement from Clearwater Cylinder Head for under $500 and install it in an afternoon.

 

At the moment, it seems the new Stant 16# radiator cap bought to replace at the same time as the thermostat is faulty. Just checked with a cold startup and it was leaking around the cap's rim. Pushing down on the cap stopped it. Took it off and cleaned the seating areas and it still was leaking. Put the old one on and the startup leak stopped. We are going to monitor it for a while and see if anything more develops. Thanks for the 'head's up' on the testing info and cylinder head sources. Have already checked on the Clearwater head, but it is on standby until the problem (or lack of one) is resolved. Thanks again!