Cooling help

[bigred94]

Hey guys a bought a 91 yj 4.0 that apparently had been setting for a while. The whole cooling system was gummed up with slush. I flushed the radiator, heater core lines, upper and lower rad hoses. I replaced the thermostat and water pump along with new radiator cap. Now radiator was replaced before I bought it. The temp gauge comes and goes so that’s a latter day fix.
My problem is when I put it on the road, less than a mile, it starts spitting coolant from the radiator cap all over the place. What am I missing? When I flushed the radiator from cap it flows heavy from lower port. I backed flushed and filled the heater core and block.

 

[Gilaguy23]

First off it sounds like somebody either dumped a can of the bars leak crap into the engine or used uncompatible coolant types with each other. That in itself can make a gummy mess thats really hard to clean out. If its puking coolant out the cap a few things may be happening. Overheating is one, overpressuring of the system from a bad head gasket or cracked head, the other is more of the sludgy crap that was in the system being loaded up under the rubber seals in the cap and the rad seating area. This dissallows the gaskets to seat and also prevents them from working correctly to draw coolant back into the system from the overflow bottle once cooled down.
In bad cases like you may have had I would remove the hoses off the heater core and rad and flush them really good. Remove the thermo and with the upper hose on the engine flood the engine constantly with a hose to clear out any crud. Take a leaf blower and blow out the skanky water in the block and repeat as many times as it takes to see clean water in it. You really need to have the temp gauge working to see whats going on as well and unfortunatly the rad core may be really gummed up even when the water pours out the bottom of it, the temp gauge will thell all once fixed.

 

[Flyer58]

When I flushed mine I used the Prestone flush and let it set to two days during which I started it and did a very short drive up the road and back. It won't dissolve the metal by letting it sit longer, in fact they recommend it.

With the 4.0 make sure you elevate the front end on ramps or a steep hill to burp the air out of the system. They have a bad habit, especially in the JK's, of getting an air bubble in the back of the head which causes huge problems.