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2001 Jeep Cherokee sport

Just bought this Jeep with 145K miles. Had radiator and all hoses replaced. The overflow tank is boiling over but the engine is not overheating. Safe to drive? What should I be checking for?

Is the overflow over filled?

Sounds like a bad radiator cap not holding pressure. Or the sealing surface of the radiator where the cap fits is too rough to seal.

+1 for pete peters. A bad radiator cap is the main suspect.

I’m betting it’s a blown head gasket or cracked head (not uncommon with these). A shop will be able to tell with an exhaust gas sniffer and a pressure test. If a new cap (cheap) doesn’t solve the problem, get it to a shop pronto!

Rod Knox, nope, overflow resovoir is not overfilled. Thanks for all the suggestions folks, hoping it’s not a gasket or cracked head. They put a new cap on with the new radiator, still try a new cap?

And only have had the new radiator for 2 weeks! Hope this doesn’t cost a boatload to fix!

Boiling over. Hmmm… Are you sure it has the correct coolant/water mix, or the recommended coolant in it? That and lack of pressure (bad rad cap) lower the boiling point.

Other than that, you could check if the engine is overheating (bad thermostat), or another engine problem (blown head gaskets, etc). All those can cause issues. You say it’s not overheating – I’m assuming you judge that by the gauge on the dash? It’s probably unlikely that has failed, but it’s possible. Does it warm up properly?

Often folks think it’s ‘boiling’ when it’s a blown head gasket forcing exhaust gas into the overflow tank.

Does anyone else feel confident in identifying the smell of exhaust gas excaping from the cooling system? While I would always verify my ‘smell test’ with the chemical sniffer my nose has never failed me.

And don’t all shops use a product like this?

My thinking is along the same lines as that of texases.
If the engine is not running hot, but the overflow tank appears to be “boiling”, it is very likely that the OP is seeing the “bubbling” effect of exhaust gases in the coolant, and a breached head gasket would be the likely cause of that situation.

@Rod Knox

I actually have that EXACT tool in my toolbox

Around here, we call it a block tester

Since the radiator cap is new, It does sort of sound like a compromised head gasket. Before tearing the engine apart though you’d want to confirm that idea either by the chemical test above and/or ask a shop to do a cooling system pressure test. If the cooling system doesn’t hold pressure, even if it just the cap, it will definitely boil. Usually when that happens it also overheats.

Unfortunately, it looks like the 2000 and 2001 Cherokees with the 4.0 l engine are famous for cracked heads: