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94 jeep wrangle cooling problem
03-10-2008, 10:31 PM
Post: #1
Question 94 jeep wrangle cooling problem
vehicle was leaking fluid from under vehicle when i stoped by the store. checked under vehicle and it was coming from the waterpump area. I drove the vehicle back to my house didn't overheat it, temp stayed below 250. I had just changed the thermostat and drained and refilled the radiator a week prior to it happening. I changed the waterpump but when i was refilling the radiator it reached the top so I started the vehicle so the fluid would continue in the radiator so i could add more antifreeze. the vehicle continued to get hotter and pust antifreeze out of the top of the radiator. seemed like the thermostat never opened. a couple of people said it may have gotten to hot and cracked the head or block but i checked the oil and there is no sign of water or antifreeze in it. I'm just looking for some advice on what I should check
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03-10-2008, 11:38 PM
Post: #2
RE: 94 jeep wrangle cooling problem
Not sure of the sequence of events from your post. Is it leaking now or has that been fixed by your recent repairs? (water pump and t-stat)

250 degrees is HOT in anyone's book and at that age you could have a leak on the outside of the head gasket without coolant showing up in the oil. (coolant leaking on the ground) The sure way to find that is with a pressure test. The fix is a tear down for replacement of the gasket.

As for the coolant pushing out the top of the radiator, we have several reasons that can happen. The most simple reason is you have the t-stat installed backwards. (the springy part goes toward the engine)

Other ways that can happen are a bad head gasket or a cracked head. Either way compression from the cylinder is leaking into the cooling jacket and there's no way to tell which one is at fault without a tear down. OTOH, you can do a pressure test of the cooling system with the spark plugs out to see if a cylinder fills up with coolant. That's where you need to go if there are no external leaks and the t-stat checks out.

Rupe
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03-11-2008, 09:11 PM
Post: #3
RE: 94 jeep wrangle cooling problem
Rupe Wrote:Not sure of the sequence of events from your post. Is it leaking now or has that been fixed by your recent repairs? (water pump and t-stat)

250 degrees is HOT in anyone's book and at that age you could have a leak on the outside of the head gasket without coolant showing up in the oil. (coolant leaking on the ground) The sure way to find that is with a pressure test. The fix is a tear down for replacement of the gasket.

As for the coolant pushing out the top of the radiator, we have several reasons that can happen. The most simple reason is you have the t-stat installed backwards. (the springy part goes toward the engine)

Other ways that can happen are a bad head gasket or a cracked head. Either way compression from the cylinder is leaking into the cooling jacket and there's no way to tell which one is at fault without a tear down. OTOH, you can do a pressure test of the cooling system with the spark plugs out to see if a cylinder fills up with coolant. That's where you need to go if there are no external leaks and the t-stat checks out.

Rupe
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03-11-2008, 09:18 PM
Post: #4
RE: 94 jeep wrangle cooling problem
I have chaged the thermostat and water pump and there is no leakage on the ground. Thermostat was in correctly. The vehicle starts and runs fine, no misses, no leakage when running. I also pulled a couple of plugs and looked at them and there was no sign of water or any other moisture. Checked oil again and looked for white smoke or moisture from the tail pipe. Tried to run again and fill with fluids, but it did the same thing, temp gage said it was running at 240-250. had the radiator cap off so I decieded to check the water for heat it was ice cold. Also felt the top hose and it was not hot in the middle and was just warm next to the thermostat housing. So I am still where I was yesterday. Any more sugestions? Wouldn't the vehicle run crappy if the gasket was blown or a cracked head?
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03-11-2008, 09:20 PM
Post: #5
RE: 94 jeep wrangle cooling problem
how do you do the pressue test of the cooling system?
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03-11-2008, 10:46 PM
Post: #6
RE: 94 jeep wrangle cooling problem
To do a pressure test you need a nifty little gadget called a "radiator pressure tester" which is available at most parts stores (guessing in the $40 - $80 range, depending) or maybe you can borrow one.

Basically, it fits in place of the radiator cap so you can pump the system up to working pressure and see where the leaks are. External leaks will eventually show up on the ground (you still need to look closely and fix them) while internal leaks will show up as water in the cylinders or oil. In the case of a very slow internal leak you may need to pressurize the system then walk away for a half hour. If the gauge goes down (loss of pressure) you remove the spark plugs and turn the engine over slowly with a wrench while watching for any coolant at the spark plug holes.

There are a few other things you can use a pressure tester for but I'll save that for another time.

Or course all of the above presumes you have exhausted the normal items like an air pocket in the system, restrictions in the system, or any odd accessories. (outboard block heater or aftermarket AC system?) Anything that inhibits the coolant flow or the air flow can cause similar symptoms. You mentioned the top hose is not hot, yet the gauge reads hot. That tells me the coolant is not flowing.

BTW, you didn't mention if the old coolant was really nasty / rusty or if it was fairly clean. That might also give us a clue.

Rupe
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03-12-2008, 09:15 AM
Post: #7
RE: 94 jeep wrangle cooling problem
Rupe Wrote:To do a pressure test you need a nifty little gadget called a "radiator pressure tester" which is available at most parts stores (guessing in the $40 - $80 range, depending) or maybe you can borrow one.

Basically, it fits in place of the radiator cap so you can pump the system up to working pressure and see where the leaks are. External leaks will eventually show up on the ground (you still need to look closely and fix them) while internal leaks will show up as water in the cylinders or oil. In the case of a very slow internal leak you may need to pressurize the system then walk away for a half hour. If the gauge goes down (loss of pressure) you remove the spark plugs and turn the engine over slowly with a wrench while watching for any coolant at the spark plug holes.

There are a few other things you can use a pressure tester for but I'll save that for another time.

Or course all of the above presumes you have exhausted the normal items like an air pocket in the system, restrictions in the system, or any odd accessories. (outboard block heater or aftermarket AC system?) Anything that inhibits the coolant flow or the air flow can cause similar symptoms. You mentioned the top hose is not hot, yet the gauge reads hot. That tells me the coolant is not flowing.

BTW, you didn't mention if the old coolant was really nasty / rusty or if it was fairly clean. That might also give us a clue.

Rupe
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03-12-2008, 09:18 AM
Post: #8
RE: 94 jeep wrangle cooling problem
Yes, that is the case with the top hose and water in the radiator being cold, but the engine reading hot. When I first drained the radiator it was green and looked kind of nasty. Should the vehicle run fine or should it run rough and miss?
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03-12-2008, 10:50 AM (This post was last modified: 03-12-2008 10:54 AM by Rupe.)
Post: #9
RE: 94 jeep wrangle cooling problem
Before I jump into a long post on the t-stat itself I suggest you remove it completely and see if that doesn't help with the over heating issue.

If the engine runs rough you have a problem. At the moment I can't say if it's related to your over heating, which is why I was I was asking you to do a pressure test with the plugs removed.

Head gaskets and burned valves are common enough on that vintage to make it worth eliminating that before jumping to conclusions. Do you have a compression tester available? That will tell you if there are any burned valves and give you an idea of how much $$$ you are in for once things come to the tear down stage.

Coolant is supposed to be a bright light green and semi transparent. If there were any lumps, scale, flakes, crust, or brownish tinge it should have been flushed before the refill with fresh coolant. OTOH, that usually doesn't stop it from flowing completely. I suspect you still may have a t-stat problem of some sort or the system is air bound. (a bad head gasket will put air into the system)

Rupe
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03-12-2008, 09:16 PM
Post: #10
RE: 94 jeep wrangle cooling problem
ok, i'm going to try it without the T-stat and see what it does. Also have a question, should the vehicle be on level ground when filling with fluids? Will this cause a air pocket if it is not? My front end is lower than the rear end, slight grade. Since this is a 4 cyl. I would think that it would run rough, but it runs fine. If it were internal leakage into the cyl woundn't this cause the vehicle to miss. Thanks for all the help you have given me so far.....great info
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