Why is my coolant boiling?

[MrFreeze5]

Now that you have solved the overflow problem, once you replace the bottle and cap you can work on the cooling problem in slow / stopped traffic.

 

Earlier you said that you replaced the water pump and thermostat and the fan clutch being weak but did not mention the condition of the radiator or the lower radiator hose. If the radiator is clogged or dirty it can restrict the flow and as posted in another thread if there is no spring in the hose it can sometimes collapse restricting flow.

 

I have an 88 with the 4.0, 5 spd, 4wd, and a/c (not working but connected) and when I replaced my radiator I put in a 2 row core. Mine also has an additional electric fan that was rewired to a toggle switch and had to be on all the time. I reconnected the wiring to the fan sensor so it works automatically. When I hit stop n go traffic in construction or rush hour in 85+ heat my temp gauge dos not go up and the electric fan has not come on yet.

 

 

Aside from the boiling issue, it seems to cool just fine, especially now that I have the clamp on the cap. It still boils, but it takes longer to get to full temp, and remains steady. Before it would fluctuate as much as 20-30 degress depending on traffic and how fast I was going. I have not had to top off the bottle yet, and I am going to see if I can go a bit longer than before without refilling. The tstat is doing its job so long as there is enough coolant in the system and it maxes out at about 210 sitting in traffic.

 

The rad hoses are good enough for now, and arent collapsing, even though the lower seems to be missing the spring inside. The radiator itself has no leaks or obvious damage and looks to be in good shape for its age, at least from the outside.

 

Next week, I plan on doing a tune up on the MJ. Rad hoses, new CCV elbow, spark plugs, cap, rotor, air filter, and oil change. Ill check the radiator at that time. I do not have AC, but will be retrofitting an electric fan as soon as I can manage to go pick it up.

 

In a little while, I am going to go out and check for cracks in the bottle neck since it still seems to be losing pressure regardless of the clamped cap. I wouldnt be surprised if the opening was cracked or something.

[MrFreeze5]

Lookey what I found. Its is a crack about an inch long between the threads of the bottle and is visible from both inside and outside. This must be why I am not maintaining pressure. At least I hope it is :brows:

 

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[comanche12]

tho so that bottle is cracking... lol told u to get metal one ;)

[MrFreeze5]

Got some confirmation today! I hit up Taco Hell today. Temps were good and actually didnt even hit 210 until I was on my way back home. I usually take the back way through the neighborhood to avoid all the other stupid people on the road, but decided to hop on the main road so I could avoid the stop signs. Driving at speed for a mile brought the temp back down below 200 and when I got home, it wasnt boiling at all. So I guess my propensity to take the back way was keeping temps higher.

[SW86]

ive got a similar problem. when the truck warms up the coolant boils pretty quick and then when i turn the motor off theres smoke coming from the valve cover. ive read this thread a couple times and still don't quite get it. i havent replaced anything to do with the cooling system but hell i don't know where to start. :dunno:

 

sorry for the :hijack: :nuts:

[MrFreeze5]

ive got a similar problem. when the truck warms up the coolant boils pretty quick and then when i turn the motor off theres smoke coming from the valve cover. ive read this thread a couple times and still don't quite get it. i havent replaced anything to do with the cooling system but hell i don't know where to start. :dunno:

 

sorry for the :hijack: :nuts:

 

 

Mine would do that when the coolant got too low and despite my new valve cover gasket, it still leaks oil slightly. When the temp would spike, it would start burning the leaked oil. But it would only do this to me when I havent topped off the coolant for a while and it gets too low and doesnt cool anymore and the temp spikes into the red. But my truck does not smoke when its at normal temp. If the coolant is boiling badly, I may get a little steam coming out, and with the hood closed, it looks like smoke coming out the front, but just a little.

[jimoshel]

Gave my GF a '89 XJ to drive,4.0, auto, 2wd. It kept overheating badly. Finally got tired of listening to her complaining about the smell and smoke and constantly having to refill coolant so I attacked the dern thing. Obvious, and easy, things first. Fan belt and aux fan OK. Thermastat OK. Apparent normal coolant flow thru heater and htr hoses. Removed temp sending unit, the one on the back of the head. ????, nothing. No coolant flow, nothing. Poked wire down hole. Wire hit resistance, came out wet but still no coolant. Got air hose, applied air 90psi to hole. Nothing. Applied air, 20psi, to pressure bottle. Nothing. Dropped exhaust manifold, removed rear freeze plug. Nothing. Block was so full of crap it was practically solid. Got pressure washer and long wire, started probing around in hole. Note. When probing around freeze plug hole, DRAIN COOLANT FIRST! After removing thermostat housing, thermostat and lower radiator hose and heater hose proceeded to flush clean out block. Used a 1/4in cable to push into all and every opening I could find while running water thru the block. After flushing out about 3 coffee cans of crud and crap I did the heater and radiator. They were clean. Just the block was dirty. Put everything back together again and test drove XJ. Temp gage went up to 200 and stayed there. No more problem.