I've been researching since I picked up my 2000 Cherokee with 167,000 miles about a month ago.
My coolant level in my overflow bottle is always getting low. I've taken it in and had a pressure test done on the radiator and and they did a block test as well. Everything checked out ok. I'm not seeing any sign of coolant in the oil or oil in the coolant. Cannot see any leaks. Cannot see a crack through oil fill hole, do not see coolant through oil fill hole while engine is running. No steam from exhaust. No coolant smell. Engine runs very strong.
I would not think anything is wrong except the low coolant. The level in the radiator itself is always full. Mechanic tells me to monitor the radiator and not the overflow bottle.
Any help would be appreciated. What else am I missing?

 

Was radiator cap also pressure tested ?

 

At this point, I would follow your mechanic's advice. Watch your engine temperature and monitor coolant level in the radiator. It could be that the PO did a coolant flush recently and failed to open the heater core or just had air in the system that is being purged from the lines. Give it a month or so, refill to proper level and continue monitoring.

 

2000?

Watch for the head to crack...

 

Not sure if cap was tested. Might try to pick up a new one.
I'm very aware of the head problem. That's what I was referencing in my first post.

 

Have you "burped" the system lately? May just have air in the system that is slowly working its way out.

 

If the cooling system, block, head and gaskets/seals are actually in good condition, the system could be slowly "self burping". If the mechanic told u to monitor the radiator and NOT the bottle, he is wrong......BOTH must be monitored. If the bottle is allowed to run run dry, u can bet air will enter the radiator. The rad cap is a 2 way valve....it allows both coolant and any air to escape the radiator (hot coolant expands) but only allows coolant to return to the radiator (cold coolant contracts). In a properly functioning system (no leaks anywhere), with a good rad cap, thru the normal heat/cool cycles of the motor, all air in the system escapes and only coolant remains. Again, the bottle cannot be allowed to run dry. When the motor is COLD, the bottle should be +/-1/3 full and the rad should be full to the top of the neck. Check them both frequently.

 

My 2000 slowly loses coolant as well due to a leaking heater core and I don't always smell it inside the cab. I bet that's your problem as well.

 

Seems like the pressure test (that was done) would reveal a leak due to pressure not holding during the test.

 

Exactly what I was thinking. I just picked up a new radiator cap, so I'll see what happens. No sign of a leak anywhere. I will try to burp this weekend. I wouldn't be stressing so much, except I've read so much about the cracked heads with this year. But can't find any sign of a cracked head. I guess I could pull it off and have it checked, but if I go that far I'd just end up changing it out.