Boiling coolant issues!!

I've got an '87 XJ 4.0L with an odd coolant issue. I have read all the threads on coolant and over heating but nothing compares to this particular problem. Whenever I start the truck the temp slowly increases and runs all the way into the red and my coolant bottle smokes and looks like it is about to explode. I have replaced the coolant bottle and thermostat but ti still does the same thing. I have noticed that the electrical fan does not run at all but does operate when connected to a power source. Has anyone had a problem like this before?? ANy help would greatly be appreciated.

Sounds like you have air trapped someplace in the system. Try a search for "Burping".

The problem is that your electric fan should switch on when the gauge is reading ~220*F to cool the engine down again. That isn't happening and the question is why. There are two possible reasons. If the fan doesn't switch on when you operate the A/C or the defrost, the fan relay is blown. If it does switch on when you use the A/C, that means the coolant temp. sensor in the radiator is defective.
Your viscous clutch fan should also help to keep the engine cool when idling. Since your gauge is going into the red, it obviously isn't doing its job and the reason for that is a bad viscous clutch. You'll need to replace it.
Finally, I suggest that you get your radiator chemically cleaned and flush the entire cooling system. If it's the original 17-year-old radiator, it's probably had its day and long overdue for replacement. If the flush doesn't work and the engine overheats despite fixing both fans, replace the radiator with a 2-row Modine unit.

Pull the thermostat and see if it does the same thing, it's cool up there in NH right now so this is something you want to get fixed. If it still overheats with the thermostat out then you either have a blockage, pump is shot. Was this a gradual thing or did it just all of a sudden start doing it one day ??
Also one BAD overheat can ruin a thermostat. In real life the XJ should be able to idle all day on just it's main fan, even mine, a 98, at over 230,000mi does not kick on the aux fan when I'm in the woods, only time it comes on is when the A/C compressor comes on. Also check your plugs, see if one is vastly different than the others, possible that you have leaky headgasket.
If you want to do the less expensive route to start drain the system, refill with water and add prestone 7 hour flush, though with it overheating like that you might have a tough time doing that drive time. If you want it fixed just go get a modine radiator and be done with it. If this is the first R&R on the cooling system you might also want to do the hoses as well, just make sure the lower hose has the spring inside to prevent it from collapsing under suction. Refill with new coolant and distilled water [not springwater].
It might also be a really good idea to have one of the plastic mixing valves on hand, they tend to self destruct with age and alot of reported them falling apart when trying to remove the old hoses and put new ones on. I think someone said that the new ones are made from metal now but I have only seen the plastic ones.

RichP said:

In real life the XJ should be able to idle all day on just it's main fan, even mine, a 98, at over 230,000mi does not kick on the aux fan when I'm in the woods, only time it comes on is when the A/C compressor comes on.

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Depending on the outside temperature. The above is true. If you are idling for very long on a 90 degree day you'll need the aux fan for sure.

Is saw that you replaced the bottle, what about the cap? Those caps go bad pretty easy.

The basic problem may be simply that your XJ is a 1987. The factory radiators are only good for about 10 years, and that's if you use distilled water and change the anti-freeze every couple of years. I have an '88 and the factory radiator gave up about 4 years ago. I suspect that if you remove your radiator and take it to a shop, they'll find that it's almost 100% blocked.

I second the Radiator, my 87 was all about overheating (highway, trails)
until I replaced that POS clogged unit.


Replace it with a new 3-Core along with the water pump, coolant bottle, cap, and regular "Green Antifreeze", not that Dex junk.

I was having cooling issues with my 88 (until Eagle set me straight) new radiator, new surge tank (and cap) and plugging up the leaks, took care of most of the problems. Also replaced the thermostat with an OEM, which has a air bleed hole, to help move the air along. New fan clutch, is my next purchase, installed a manual switch for my aux. fan, just in case. Simple installation, bought a 10 foot piece of two lead wire, already insulated and piggy back spliced (soldered) the two wires onto the thermo switch leads, near the connector and ran it beside the harness, to a switch inside. Tested my temp. switch (lower left of the radiator) in a pan of boiling water, with a ohm meter. Tried 2, they both switched at about 207F. Haven´t tried a new one, have heard they switch on (close) at a higher temp.
When I refilled, I removed the gauge, sending unit, at the drivers side rear of the block and filled until coolant came out. Then topped it off, with the sender back in (do not use sealer/messes with the ground). Top radiator hose is an air trap, squeezing it together a few times, moves some more air along the system.
Had an 87, after most any kind of radiator service, it would blow some steam, unless I had thoroughly, burped most of the air through the system. Air gets trapped on top, causes a partial blockage, possible the temp. switch for the fan, at the bottom of tha radiator doesn´t get hot enough to turn on, even though the top is blowing steam, seen it happen.
Doesn´t take to much of a leak, to suck a little air at a time and have the air build up, to the point it messes with the flow, then everything overheats. System builds pressure and forces a little coolant out, then when it cools down it sucks a little air in, air moves to the top and stays there (mostly), eventually moves to the surge tank, hopefully before the motor overheats.
Last thought, the universal type thermostat gasket, doesn´t have the cut out for the surge tank/heater hose bypass. Bound to have an adverse affect on how the system works, if the gasket is covering the bypass slot.

Sounds to me like classic head gasket failure.

Digger87xj said:

Sounds to me like classic head gasket failure.

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Could be, if it´s leaking that much, a leak down test, should show some bubbles in the surge tank. Vapor/fluid out of the exhaust or even the surge tank bubbling and smelling like soot are indicators. That time of year though, high humidity, cool dense air, a little fluid out the exhaust doesn´t mean much, often.
I´ve had almost the exact same thing happen, with an air block though, top of the motor overheats, makes steam and the surge tank swells up. Also the top radiator hose, swells and gets really hard.
Check the easy stuff first. Air blocks, in the closed system, are pretty common.

Ok I ran the truck today to check the mech. fan clutch and I have determined that the clutch is baked. Will this and the fact that my electric fan not working cause such an overheat?? There is no carbon or soot smell from my pressure bottle, just coolant. The bottle and cap were changed together. I have replaced the aux fan relay. I have also replaced the thermostat. How can you check for a bad water pump? All hoses are really hot. The top radiator hose is extremly hot and hard as well. I'm beginning to think that my radiator is toast and coolant isn't getting to the temp switch to activate the aux fan. I will try to burp it. I have seen several threads on burping. Is the parking the jeep uphill and pulling the heater core hose trick the best way?

Whoa, first how did you come to the conclusion that the clutch fan is shot?
Second, yes if both fans aren't working it most certinatly will overheat.
Third, Perhaps the reason coolant flow isn't going thru the top hose is the fact that the thermostat is stuck closed.

Remove the thermostst and try it.
The temp unit for your fan is on the radiator tank on the drivers side perhaps you should make sure its working.

jeepguy97 said:

Third, Perhaps the reason coolant flow isn't going thru the top hose is the fact that the thermostat is stuck closed.

Remove the thermostst and try it.
The temp unit for your fan is on the radiator tank on the drivers side perhaps you should make sure its working.

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He just said that the top radiator hose becomes hot and hard, so that indicates that the thermostat is opening properly.
Since he's replaced the auxiliary fan relay and the fan still isn't working, it's a dead cert that the coolant temp. sensor isn't working. The reason for that may be a bad sensor or the radiator could be so clogged up that coolant isn't reaching the sensor to allow it to function properly.
Like I said, if it's still the original 17-year-old radiator, it should go in the garbage can and be replaced by a 2-row Modine unit. This is also a good excuse to convert to the '91+ style open cooling system and save yourself having to "burp" the system each time you replace the coolant. You can also get rid of that crack-prone PITA called the pressure bottle.

I ran the truck until the engine was nice and toasty. Then I shut the engine off and I went to move the mechanical fan and it moved extremly easy. I agree with Dr, Dyno...I think my radiator is baked!! I just don't know if it is original or not. This problem just came up out of nowhere. I'll try to burp it but I have a feeling that I'm wasting my time. Is it common for the temp switch to go?? Thanks for everthing guys!

The fan clutches on these Jeeps are always easy to move, they are weak. That ain't your problem. I bet the thing would overheat at 80 mph, which, at that speed, you could remove all the fans and it would cool fine if the system was in good shape. Fans are for stopping and slow speeds only. You probably simply have air in the system, which is why your fan isn't kicking on. Does you heat blow cold air? If so, you just need to burp it. This is a hugely common problem on these dumbass designs, and it is tough to get the air out. Furthermore, the temp gauge is inaccurate. It may be in the red, but its probably reading air, not coolant. To tell you the truth, you could run it pretty hot and be ok, but you'll need to burp it to get hot heat. I wish I could tell you how to do this, but I have tried on many different ones for a long time and never gotten it right.

Jackhill442 said:

The fan clutches on these Jeeps are always easy to move, they are weak. That ain't your problem. I bet the thing would overheat at 80 mph, which, at that speed, you could remove all the fans and it would cool fine if the system was in good shape. Fans are for stopping and slow speeds only.

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That's basically correct as far as the fans go, but the stock clutch fan is essentially useless and that IS a problem if your engine overheats in the city or on a slow trail. You could remedy that problem simply by having dual electric fans that are thermostatically-controlled, with the option of a manual toggle switch to operate them on slow trails.
If the engine overheats on the highway, replace the radiator. There's enough ram air effect above 30mph to render cooling fans unnecessary. If the engine doesn't stay cool in that situation, it's because there isn't enough coolant circulating through the radiator (or it can't circulate because the radiator's clogged up with debris).
You will cure your cooling problems by:
1. Replacing the radiator and both hoses (the lower one has a spring inside to prevent it collapsing under suction from the water pump).
2. Converting to open style cooling system (gets rid of that POS pressure bottle and the open system is "self-burping").
3. Replacing the POS clutch fan with a 14" Zirgo electric fan from e-bay(mounts to stock fan shroud).
4. Replacing the faulty coolant temp. sensor (or "switch" as some people call it).
5. Robertshaw 195* t'stat from http://www.flowkooler.com

When your water pump finally takes a dump, you can replace it with a Flowkooler high-flow unit.