Air in coolant 4.0 -
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Unread 10-14-2007, 07:29 AM   #1
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1998 TJ Wrangler 
Join Date: Apr 2007
Location: Maple Park, IL
Posts: 152
Air in coolant 4.0

Hey guys what is the trick to getting the air out of the coolant system on a 4.0. I had to change a leaking freeze plug and I can not get the system to take coolant? I done some checking on google and they say the 4.0's are famous for getting air in the head, but no luck on finding any info on purging the system???????

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Unread 10-14-2007, 11:12 AM   #2
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1993 YJ Wrangler 
Join Date: May 2005
Location: Colchester, VT
Posts: 939
fill the rad completely with coolant and run the jeep until the t stat opens you'll notice a drop in the coolant level and keep filling until you see no bubbles and a steady flow of coolant. that's what i did just kept adding you'll see the level drop every now and then just add to it.
1993 Jeep Wrangler
4.0L Tom Woods rear HD shaft
D30 w/yukon alloys, lock right, jb4x4 bracket, Rusty's HD tie rod 8.8w/ LSD,SOA xj rear 100" wheelbase, homemade greasable boomerang shackles, SS braided lines, 1" prothane body lift, 35" TrXus M/T, smitty built XRC.
lots of gen right armor and rear stinger.
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Unread 10-17-2007, 12:35 AM   #3
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1989 XJ Cherokee 
Join Date: Jun 2005
Location: in a yellow house
Posts: 653
On the back of the head(driver side)there is a sender screwed in for the temp gauge,loosen but don't remove it completely.Start engine and let it get up to operating temp....the air should seep past the threads because this is the highest point...... coolant starts dribbling out letting you know all the air has escaped.
One other thing that helps is to drill a 1/8" hole at 12 and 6 oclock position in the thermostat flange to help air escape(most t-stats have this already some dont)
89 xj 5.5 rubicon express,34" swamper ltb's
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