So yes, I'm probably an idiot, but I'll be heading out on some long road trips soon and would like to check if I've done my rad flush/fill right (98 Cherokee sport). Originally, the radiator overflow/fill jug was over the add mark, just below the full line. The fluid was very dark brown and nasty, so thought it was time to clean out the rad. Vehicle runs great and doesn't overheat, but thought it'd be proactive.

Got a flushing tee, hooked up the garden hose and cycled clean water through. Closed things up, ran it a bit, drained coolant and repeated the process. After draining coolant the second time, the reservoir was still full, so I removed it and dumped out the junk. Was surprised to find no outlet on the jug. Just a cap for filling, and the hose coming in from the rad overflow line. I put the reservoir back empty, and filled the rad through it's cap with straight anitfreeze. Only got about 6 L in (wasn't completely drained I guess?), but since total capacity is about 12L, figured the mix would be ok.

Am wondering about the reservoir now though. Why on earth does it have fill/full lines if I'm not supposed to put fluid in? How could there have been substantial fluid in it in the first place? Seems impossible to overfill the system. Filling via rad cap, it just overflows if too much is added. After a few weeks of driving around town, no additional fluid has entered the reservoir (it's still completely empty), and the coolant in rad is to the top when I remove the rad cap....Is this enough? Should there be fluid in the reservoir or no??

Thanks for the help!

 

Prior to the mid 70s cars didn't have overflow tanks at all, if the rad was filled to the top when cool after it was warmed up the excess warm coolant was just puked out the overflow tube onto the road. The overflow tank just provides a bit of extra coolant for varying operating temperatures without wasting it. The rad will overflow into the overflow as it gets hot & suck it back into the rad when cold. All due to thermostat operation.

So you will have 2 marks on your overflow tank, a lower one & an upper one. When the engine is cold you should remove the overflow's cap & fill the overflow tank to the lower mark (some cars will say "full cold" on their tanks at this point). If you check it warm after driving for a while the coolant will have risen to the second mark (=full hot). If you have no leaks your coolant in the overflow will cycle from the lower mark to the higher mark as you operate your vehicle with no further action required.

Hope this helps.

 

Thanks! And interesting tidbit, glad we don't puke it on the road anymore!! The one thing i don't get is how does the rad suck coolant back from the reservoir when the only hose is at the top and the full reservoir fluid line is far below that? it doesn't turn to gas, and fluid can't be sucked up through a pocket of air?? I can see how the overflow comes in, just not how it cycles back out when needed...always thought there was another hose at the bottom which would open to rad to accept fluid depending on temp....should there be another tube attached to the outflow hose on the inside of the reservoir to reach down to excess coolant?

 

Most overflow bottles hoses go directly to the bottom of the tank, the XJ's is a little weird-I just looked at mine to be sure of how it works. You will see that the flexi hose attaches at the top of the tank to an integral stiff pipe that then heads to the bottom of the tank! So no voodoo there, LOL.

Where are you in the Okanagan?

 

Ah hah!, yes i see now, thanks! Always feel better when i know what's going on. First road trip went A.O.K. I'm in Kelowna