Ever since I've had my XJ the coolant reservoir level has always been on the "add" line. It was this way even after I did a coolant flush about 6 months ago. The Jeep has never overheated and the gauge always reads right at 210 degrees as normal. Earlier this week I checked to see if the coolant might be low in the radiator so I popped the rad cap while it was running. At first the coolant was right at the lip, then it started to dribble over. I don't know what's going on and no matter where I look online, I can't seem to find a clear answer. Do I have leak? Air in the system? Any help in answering this is greatly appreciated!

 

I should add that I've tried adding to the reservoir, getting the level back up to the "full" line. A few days later after driving it around, the level went back to the "add" line and has stayed there ever since.

 

Crack in bottle maybe ?

 

Look in the corners of your radiator and see if they look wet. You could have pinhole leaks in the corners, possibly accounting for the coolant loss.

The bubbling over happens when the coolant heats up and expands, about the time the thermostat opens, and will recede afterwards, both due to coolant loss out the open cap hole and into the block. The coolant bottle has a hose that feeds into the filler neck, which sucks in coolant as the system cools off when you turn off the engine. I would assume the reverse is also true when you get too hot. Keep it full, but look for leaks.

I've been putting off a total cooling system replacement for 2 years, needed due to those pinholes in the corners. Somehow I've limped along this long, going to do it in the fall. I don't really have issues as long as the reservoir is full. YMMV

 

A properly functioning radiator cap is an absolute must in a "open" type coolant recovery system. Never remove the cap when the cooling system is hot. When the motor is cold, check coolant level in the rad.....it should be full the top when cold. Coolant level in the bottle should rise/fall with heat/cool cycles. The bottle MUST always have some coolant in it hot or cold.

 

how much is some? When my engine is running the coolant level is below the add line.

 

Just fill it up.

 

Did you ever solve this i have a similar issue?

 

It may not be an issue unless your vehicle runs hotter than an XJ should, or the water in overflow bottle keeps falling (does not stabilize at a satisfactory level)

bear in mind the electric fan does not even turn on till 105C = 221F

SO, if your vehicle will idle in hot weather, or pull a long grade, and the coolant temp does not keep rising above 220F, your XJ is NOT overheating

Having said that, one an older cooling system, the possibility of leaks exist

If you have +10yrs rad, hoses, water pump, thermo housing etc, good chance they may be starting to leak

Best way to find any leak is to pressurize the cooling system via rad cap with a test kit. If you do not wish to buy the kit yourself, take it to a good mechanic, or radiator specialist, and they can do it in front of your eyes in 5 minutes

(XJ have a way of leaking in the front of the radiator that cannot be located visually, runs down and across front, but you can HEAR it hissing!

 

Typically with any coolant leak, the smell gives it away long before the leak is detected.

 

There was a pinhole leak in my coolant reservoir bottle that I found while doing a coolant flush, was doing the job at a friend's place and he gave me ride to Autozone and we replaced it that day. This DID mostly solve the issue, but that was also around the time my heater core started leaking so the level did still drop very slowly over time. My XJ already lost its AC from an evaporator core leak the first year of me owning it, between that, the heater core leak, a steadily rotting driver floorpan, and it being my only vehicle, I traded it back in 2014 for something in better shape. I had forgotten about this post until I got an email notification that someone replied recently. Thanks for the trip down memory lane! I still miss that old XJ sometimes all these years later.