I am about to swap my new radiator into my 91 XJ Laredo. Before I do, I wanna make sure I know how to do everything. My q is this:

How do I burp the air from the cooling system? I know I'm suppose to fill the rad with my coolant mix, then run it, and replace as needed. But how do I make sure all the air is out?

Thanks in advance.

 

One way is to fill the rad up full. Put the cap on. Fill the up the overflow tank. Start the engine, let it warm up. Once it warms up it will pull coolant from the overflow. Keep adding till the system is full.

 

Ok, because I was doing some internet research and found something about parking nose end down and removing the coolant temp sending unit on the back of the head.. But it said this was for a closed system RENIX '88 Cherokee... Is my '91 a closed or open system? What's the difference?

 

91 is open system, the difference is the open uses a normal radiator with a cap, the closed uses a pressureized bottle with no cap on the radiator. Be sure when you fill the system and run it have your heat on so that the heater core gets filled. trs80's idea works well, or you could fill radiator with coolant let it set top off if needed, then start engine run with cap off wait till tstat opens then fill as needed, I repeat, have the heat on lots of people forget to do this.

 

Check coolant level (COLD ENGINE) in the radiator for several days. Check coolant level in overflow bottle. If the rad cap is functioning correctly, coolant level in the overflow bottle should rise when the motor is hot and fall when the motor is cold. There are 2 valves in the rad cap and they both must function properly.

 

So I don't need to unplug the sender to bleed the air out? I take it open systems are a bit more simple to work with than closed. Ok, so fill, run WITH heat on and cap off, top off as needed... simple enough. Thanks for all the help.

 

And don't forget to put the cap back on BEFORE you shut the engine off, after topping the radiator off...