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Old 04-30-2012, 09:51 AM   #1
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coolant leak -- please help diagnose

1992 YJ 4.0 manual 102k miles, new to me about 2 weeks ago. Thoroughly inspected her prior to buying, and only issue was a small oil leak out of the valve cover gasket. Yesterday morning, I went to drive her i noticed a new puddle of fluid on the ground, on the driver's side a couple feet toward the center from front tire. after getting underneath her, there was coolant leaking down the upper radiator hose. I was able to trace the leak to the top of the hose, where it clamps into the radiator. Further, my coolant resevoir was nearly empty. I cleaned up the leak, tightened the hose and refilled the coolant resevoir. Drove around town yesterday, inspecting the underside each time I parked and was happy each time to see no coolant beading down the hose. This morning, I performed the same inspection, no coolant dripping down hose. However, the coolant resevoir is about an inch lower than it was when I filled it yesterday. Clearly the coolant is leaking somewhere, but I see no obvious signs of leak, as opposed to the big green puddle I saw yesterday morning.

I suspect it is the water pump, as I saw signs of corrosion around the weep hole. But I am confused as to why this problem displayed such serious symptons only once (puddle on ground and visible leak running down radiator hose) and why there is no obvious sign of a leak despite a depleting resevoir. I leaning toward just doing the water pump and seeing if that will solve my depleting coolant resevoir, but wanted to check here first. Please see photos that I took yesterday of the coolant beading down the side of the radiator hose, but as I mentioned there is no longer evidence of this.

Also, engine temp and oil temperature have been fine, no overheating. Any help appreciated....

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Old 04-30-2012, 11:11 AM   #2
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radiator overflow process

The overflow bottle serves 2 purposes. When the radiator heats up the coolant expands and needs some place to go. It overflows into the overflow bottle. Then, when it cools down, it is sucked back into the radiator.

If there is a leak, then the overflow is there to provide some extra coolant until the leak is fixed.

You ran out of coolant in the overflow. When that happened the radiator got low. When you sealed the leak and ran it the coolant expanded, but only air went into the overflow. Then, when it cooled it sucked back coolant into the radiator, just like it was supposed to do. This resulted in a drop in the coolant in the overflow bottle.

In "the day" before there were overflow bottles the radiator would always be low by the amount of that expansion. Now they are full to the rim when you take the cap off and it is cool. Keeps air from getting in and results in less corrosion.

Understanding the process helps in diagnosing problems.

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Old 04-30-2012, 12:48 PM   #3
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Thank you for that explanation, certainly explains why I have less coolant than I did yesterday. I am still a bit concerned about the cause of the sudden leak and whether I have adequately addressed whatever was wrong. Obviously I will be closely monitoring the radiator hose and fluid levels, but I want to know whether there are additional steps I should take to keep my new to me yj happy. Any insight is greatly appreciated, thank you.
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Old 04-30-2012, 02:55 PM   #4
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Ballistx is on the money. I would have replaced the hose and clamp. Once it does that it could easily happen again. I don't like getting stuck. It's easy changing top and bottom hoses.
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Old 04-30-2012, 07:36 PM   #5
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yes, i plan to replace the hose. but how do i make sure the problem was the hose and not the water pump? also, is it weird that this problem emerged suddenly and completely depleted my coolant, but then (at least temporarily) was fixed by just a couple turns of the screw?

am just trying to understand what i'm dealing with...
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Old 04-30-2012, 10:37 PM   #6
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depends on how much you had in the overflow. There could have been a fairly substantial leak and it ran out while driving. The cooling system is designed to operate at 15-18 lbs of pressure. That is the pressure that the cap will release at and let the coolant flow into the overflow.

At 15-18 lts of pressure behind a leak it will push out quite a bit of fluid. If the hose is really weak it will typically bulge at the end right ahead of the clamp. It will feel really soft also.

If it were the water pump it would be leaking around the fan shaft and typically does not heal itself.

Unless you are heading on a longer trip, the best test is just the test of time and keep an eye on it. You might check the fan for wobble while it is sitting still. If it has any side play in the shaft, then the pump bearing is going and the seal is still holding, mostly.
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Old 04-30-2012, 10:54 PM   #7
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I agree, def change the hose or hoses and clamps! cheap and easy!! I had a water pump fail a few years ago in my yj and it was not a small leak! when it went it went! if it is a small leak at water pump I would imagine that it'll get worse, fast!
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Old 05-01-2012, 10:56 PM   #8
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Water pumps never get better. When they start to go, replace them or be stranded one day.

Fun fact: Washing machine hoses bursting are the #1 insurance claim cause in the US; change em all, and use braided when available. Treat your jeeps the same, 5 years on a rubber hose.
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Old 05-01-2012, 11:27 PM   #9
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Autozone or similar parts store may rent or loan a coolant pressure tester. Really only way to properly check for leaks. Regarding the water pump, they can actually have intermittent leaks. The front seals can swell or rotate, depending on temperature and what not. If you see any staining or crust at the weap hole, it is leaking. Thermostat gaskets are common on those, and they are right above the wp.
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Old 05-02-2012, 09:41 AM   #10
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thanks for all the insight. i am debating whether to order a new wp along with new upper and lower radiator hoses. that the leak stopped makes me think that the wp may be fine (its really hard to get a good sight on the weep hole to deduce anything useful), but the thought of being stranded off road scares the sh*t out of me. i am going to see if my local napa has a pressure tester and in the meantime keep a vigilant eye on things...

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coolant , leaking coolant , water pump

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