So It all begun with me working on the jeep today at school in my auto tech program. I wanted to find out which ulley was making a growling sound. Found out it was my Idler/tensioner pulley. So then we had some extra time and proceeded to wash off the engine bay a little by hand. Nothing crazy just wipe it down and spray it with some hand spray bottles. Everything looked great and it was time to go. back to my home school (about 10 miles away)

Flash forward to pulling into my parking spot.

The temp gauge is fine running at 210 perfect when I get out I see coolent EVERYWHERE, a massive puddle on the ground and a trail into the lot. So I come out after school and decide to nurse it home (about 2 miles) I pour some water into the coolent resivoir. I get into my neighborhood and it starts idling at around 200 RPM i get it into the driveway and It all of sudden jumps to 260 and the check guages light comes on. I shut it off and pop the hood there steam/smoke coming from the head. I open the oil fill cap and smoke is coming out from there. I check the oil and its fine no water or anything. I did a quick inspection and nothing looks odd but the coolent wqas coming from the drivers side of the bay towards the front.

Any ideas?
What should I check now?

 

is it possible you might have a bad pump vs pulley,it is possible that you shorted out something for the cooling fan?you said it jump up to 260 when you stopped,bad pump or lack of airflow would be my guess,just a couple of thoughts.

 

Theres no seepage around the water pump and both fans are working as normal. Im not sure whats going on here.

Any help would be great

 

did it just boil over? if you have no noticable leaks, then maybe just a simple t-stat.

 

I'd check the radiator hoses too. I've had them spring a leak for no reason before

 

Where is the thremostat on the 4.0's? Its hard to say where its coming from I dont think it boiled over its not near the coolent overflow tank and the cap was on tight. But the system does not get any pressure with it at operating temp. The rad. hoses are very easy to sqeeze.

 

it's in the outlet where the top hose hooks to the engine. if your not pressurizing then you have a leak somewhere. if the cooling system is not under pressure it will overheat.

 

Hmmmm good info I think im gonna pressure test it and see where the leak is at.

 

Alright so after some problem solving I have found the problem. I believe it was the thermostat and it getting stuck closed causeing the pressure to build and the coolent to boil in the block. As you can see if these next picures...that is where the lower hose inserts into the block.




Quick question tho when the motor was smoking it was all coming from one area Any ideas why. Right on the valve cover. In the center of the pics.





So I went over to the auto parts store and had them hold an upper and lower rad. hoses, thermostat, and a water pump. total will be just under 100 bucks (not counting new coolent) What do you guys think just do the water pump too?

 

couldnt hurt. if you have high miles go ahead. call it insurance.

 

STOP!!!

Did you do the pressure test?

Your comment quoted above is of concern since you have an 0331 cylinder head. They are prone to cracking detween the #3 & #4 combustion chambers.

Pressure test first and if it fails pull the valve cover.

 

Agree. If steam was coming out of the valve cover, something is f'ed. I'd say cracked head. Do a pressure test. There is something seriously wrong here

 

AHHHH CRAP...lol

Alright I'll pick up a guage and do a cylinder pressure test I think I did this before thats when you thread the guage into where the plug goes and crank the motor 4 times to build up pressure then see if it holds?

 

No that is a compression test,what you want is a coolant tester that is a pump that connects to your radiator cap and then you pump it up and see if it holds,if it does not you start looking for leaks,if you do not see any leaks start looking in the cylenders with a light for any water.
doing a cylinder compression test will tell you if a cylinder is low,and if the head was cracked it would show low possibly,but a compression tester does not show a leak as they hold there highest pressure untill you release it,the coolant test will actually show a pressure drop.

 

But if my thermostat is stuck closed it wont allow that pressure to reach the block?