97 strange cooling issue. please help.

hey guys so this jeep has been quite the lemon with me but ive finally gotten everything worked out on it. except now this strange cooling issue has came up.

to start off i have basically rebuilt the entire motor. i had a lifter collapse and in turn wore a lobe off of the cam. so i tore the entire motor down and replaced the cam and all lifters and replaced the head gasket and valve seals wile i had everything off.

now the jeep is back together and running great except that it will now over heat. my heater core was stopped up so i bypassed it wile everything was apart. other then that nothing has changed with the cooling system.

what i have done so far is flush and clean the cooling system and have removed the thermostat. now the jeep runs at a good temp but every time i cut the jeep off it will spew coolant out of the radiator cap. i drove it today and the gauge only got to 215 and when i cut it of it still spews out of the cap. its like the system is just building to much pressure and i canat seem to figure out why. i have bled and burped the system many times so i dont really think there is any air in the system.

sorry for the long post but this think is driving me crazy.

97 jeep cherokee country.
4.0 automatic.
bypassed heater core.

Its common for the fluid level in the expansion tank to rise after the engine is shutoff. I believe the factory manual says that the fluid level should be between Add and Fill when the engine is at operating temperature. I keep mine around the Add level when the engine is cold, or even slightly below. If your level at operating temperature is correct, How much is blowing out? If fluid level is correct, what kind of thermostat and radiator cap? If those check out, seems like only the head gasket or head are left.

Well it seems that sometimes it will flow into the tank sometimes. It always flies out of the cap though. The jeep doesn't even have a thermostat in it right now and the cap is a newish one rated to 16 pounds. The only thing that I can think it would be is the head gasket but I'm almost positive it was put on correctly when u did it and really don't want to have to pull the head again.

If the head is cracked or warped and not seating against the gasket properly it won't seal and you'll get exhaust gases in the coolant which over pressurizes it. Though I'd expect overheating and blowing coolant more than just after shutting it off. And if it keeps overheating then its going to damage something. I would drain and refill the engine coolant and use a known good radiator cap and thermostat, consider using new dealer parts. If that does not fix the problem, pull the head and take it to a machine shop.

Well when I originally bought the jeep I got it for 200 bux with a blown head gasket. After pulling the head off i found it had a cracked head so I got a junkyard head and had it machined and installed it. It never did any of this until I put the new cam in. The exhaust burns clean and my oil is clean. It will pump coolant out of the radiator wile its still running once it gets around 210 but its very slow. Once I cut it off it almost explodes out of the cap

It shouldn't spew out around the top of the cap, no way no how. This means the top seal on your cap is bad or the top sealing surface on your radiator filler neck is not flat.

Could be a combination of things happening here. I've had the nipple near the cap for the radiator recovery hose mostly plugged. Mine was paint, yours could be calcium or water deposit flakes (you said your heater core is plugged). The hose between the filler neck and the coolant recovery bottle could be kinked. Pull it off the nipple and blow through it.

If you bypass the heater core you have to make a loop of heater hose from the thermostat housing to the pump. The cooling system needs this bypass to work correctly, especially if you have a thermostat. You also have to make sure you use the correct gasket for the thermostat housing, a universal gasket won't do, it has to be a 4.0 specific gasket.

You could be loosing radiator pressure someplace. The higher the pressure the higher the boiling point of the coolant, the converse is also true, the lower the pressure in the cooling system the lower the boiling point.

The first thing I'd do is check the cap sealing top and bottom, if the cap isn't holding pressure your chances of the coolant boiling are higher.

The I'd run the motor with the cap off and look for bubbles appearing in the filler neck. If you have a moderate to large leak of exhaust gases into the cooling system it will often bubble up at the filler cap. If exhaust gasses get into the cooling system, they can displace the coolant around the heads and the top of the motor and cause hot spots. These hot spots can boil the coolant quick.

Anti freeze doesn't only prevent the coolant from freezing, but it also raises the boiling point of coolant. The combination of anti freeze/coolant (coolant is anti freeze water mix usually 50/50) and pressure, can typically raise the boiling point of coolant to 50 F higher than plain water and no pressure. The 4.0 has a tendency to get hot spots inside the motor, especially if there is air or exhaust fumes in the cooling system.

also, make sure you don't have exhaust leaks blowing on to the motor- it wont blow the cap off -8mud nailed that part- but it will heat it up. Mine where blowing right at the oil pan and side of the block from the manifold collector. I just fixed a bunch of exhaust leaks for smog related reasons and noticed the jeep is consistently running 10-15 degrees cooler and the smell of exhaust in the cab is all gone. you can hook up a shop vac via tail pipe in reverse to find leaks easily .

blondejoncherokee said:

you can hook up a shop vac via tail pipe in reverse to find leaks easily .

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I've never thought to do that, great idea. Is there enough force in a normal shop vac to push through the cat and to produce a decent hiss at the manifold though? I was thinking disconnect the manifold and drop the down pipe out of the way.

iwannadie said:

I've never thought to do that, great idea. Is there enough force in a normal shop vac to push through the cat and to produce a decent hiss at the manifold though? I was thinking disconnect the manifold and drop the down pipe out of the way.

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I thin a little motor oil with some Diesel and dribble some down the TB. Following the smoke to the exhaust leak is fairly easy.

Cold mornings is also a good time to look for exhaust manifold leaks.

A mirror and a flashlight will usually get you in the right area anyway.

I just found one, my exhaust/intake gasket blew a chunk out the rear and it was blowing exhaust onto the firewall. My rear exhaust stud broke and fell off and likely started the whole thing.

Ok guys so heres some news. today i got a brand new cap and coolant. after work i put about 3/4 a gallon of coolant in and installed the new cap. then i drove home which is about 10 miles. when i got home the jeep was only at around 180 degrees and when i shut it off i checked underneath the jeep and it was still leaking coolant. it was only dripping out this time and not spewing out like it has been but i think that is just because of the temp it was at.

i beginning to wonder if this is a timing issue now because i know that timing can cause a motor to run hot and act weird. the only problem is that when i put the motor back together and installed the distributor it runs perfect. the motor feels like it is brand new. when i installed the distributor i installed it with the rotor one tooth past the number one post at top dead center. does anybody think that this may be my problem. i have heard of this happening on other jeeps but those were mainly the v8 zj's.

I think first off your system isn't pressurizing correctly, the pressure is leaking out. As the pressure goes down the boiling point also goes down.

When I shut my 96 down and the temp. is normal around 200 and then start it up a minute later the aux fan comes on and the temp is up around 220.

What I'm trying to say is the temperature rising after you shut off the motor is normal. After the motor is shut down it continues to circulate coolant and shed heat, but from convection and not pumped circulation, in other words it sheds heat but poorly. The temperature of the motor is likely to rise some just after shutdown, before it lowers. If your cooling system pressure is low it may heat up enough to boil the coolant. Boiling coolant does a poor job of cooling.

At 0 (zero) PSI, a fifty/fifty coolant mix will boil at around 225 F.

Find the leak and plug it up, then see what happens. You may have more than one issue here, timing would be way down my list of probable issues. First eliminate your cooling system pressurization issue then go hunting for other stuff.

Just an odd thought, water pump leaking? I know when my pump gave up on me coolant would gush out of the weep hole after being shut down. Maybe your pump is shot and leaking pressure causing what 8Mud is suggesting combined with fluid leaking after shut down?

iwannadie said:

Just an odd thought, water pump leaking? I know when my pump gave up on me coolant would gush out of the weep hole after being shut down. Maybe your pump is shot and leaking pressure causing what 8Mud is suggesting combined with fluid leaking after shut down?

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My 96 is doing exactly this right now, I have a pump to install this weekend.

Like I said, he may have multiple issues.