Coolant leaking under intake - HELP

What I thought was a lower radiator hose leak turned out to be a major leak under the intake manifold on my '90 4.0. I have no idea what could cause a leak in this area except maybe a cracked block. Anybody have any thoughts on what the problem could be?

History: My wife was driving the Jeep yesterday and noticed steam and coolant leaking when she stopped. She left it parked there and I towed it home. A quick look drove me to the conclusion that the lower hose was leaking since all the coolant that leaked out was on the left side of the engine (by the hose.) After removing the air box and electric fan (great tips - thanks) and replacing the hose, I refilled the system and let it idle. It took a few minutes for the tstat to open and then it started filling nicely. The cooling system is the stock closed system. After the system was full I let it run some more and checked underneath. It had a steady stream of water draining out and was actually spraying out of what appeared to be the side of the block. The area that has the leak is right where the preheater hose for the airbox is connected. Any help is appreciated.

it could possibly be the waterpump, sometimes when they leak, the coolant runs from the pump weep hole and follows the oil pan along the top between the pan and the engine block. however since it is a 1990, there are some freeze plugs on that side of the block that could be corroded and leaking. either way it isnt that bad of a repair.

A ruptured freeze plug could do it. The coolant was spraying out pretty good and not just dribbling.

Although less likely, the head gasket runs below the manifolds. It could be leaking outwards.

It has cooled down enough now to use the feel method on the side of the block. I am 99% sure that the freeze plug is leaking. I can feel the plug and I can feel that part of the lip that goes around the opening is missing - rusted away. Anyone ever change a freeze plug?

Just changed one on my sons xj last weekend. Its the perverbial 10 minute job once you take the 3 hours to take off the intake, exhaust and so on and so forth.
Digger

That's what I was afraid of. Looks like my weekend is now scheduled.

A quick tip is to knock one side in using a drift. Once it's in there crooked you just yank them out with pliers. Clean the opening with some sand paper and use a appropriate size socket and hammer to tap them in. I say "them" because when you replace them, do them all. Get BRASS ones! Not steel. They're around. I put a set on an old 'cuda when I rebuilt the motor.
After that no worries mate!

i believe there is 5 total, depending on which one is leaking you may be able to access it without removing the manifolds. but it usually seems to be the one that is right behind the exhaust pipe. replacing them all at once is recommended though.

Professor Bobo said:

A quick tip is to knock one side in using a drift. Once it's in there crooked you just yank them out with pliers. Clean the opening with some sand paper and use a appropriate size socket and hammer to tap them in. I say "them" because when you replace them, do them all. Get BRASS ones! Not steel. They're around. I put a set on an old 'cuda when I rebuilt the motor.
After that no worries mate!

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That's good advice and I'd certainly recommend replacing all five freeze plugs on the side of the block with brass units. They'll never rust so you'll be able to forget about them.
Unfortunately that leaves two more freeze plugs that could leak at any time so they're ticking time bombs. One's on the back of the block, the other's on the back of the head, and you'll need to pull the engine out to replace both. It might not be a bad idea to pull the engine anyway and replace all seven at the same time. Then you'll definitely have no worries!

generally speaking i wouldnt worry about the other freeze plugs in the cyl head. i have never had to replace them. usually its the one closest to the down pipe that fails. i would imagine that the heat from the exhaust that affects it the most

When one freeze plug goes, the others will inevitably follow. It has nothing to do with the heat from the exhaust, but rather it's a case of the steel plugs corroding from inside. This is inevitable when you have steel in contact with water-based coolant. The problem is even worse in engines with aluminium blocks because electrolytic corrosion also takes place.
The solution is to replace them with brass plugs because they don't corrode. You might wonder why the manufacturers don't use brass plugs in the block from the outset; it's not as if they're expensive.