Intermitent Coolant Leak

buckyAugust 1, 2006

I have an 88 3/4 Ton Chevy travel van with a good old 350 V8 engine. I can drive the old girl for hundreds of miles with no problem but every now and then I get coolant leak. Drove the vehicle on a 500 mile trip earlier this summer with no problem but today I drove it 20 miles in cool weather and it leaked again (probably a cup or two) I've tried to find the leak source but with the cabover design of the van its very difficult to see hoses pump etc..

I'm thinking that its not a hose or the pump or the leak would be consistent rather than intermitent. Any suggestions on what would cause an intermitent leak like this and where I should be looking for it? Its never overheated even in very hot highway driving. Any ideas before I start taking things apart would be very much appreciated Thanks a lot.

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Be carefull to not assume anything. Pumps can leak on occasion when they are first failing. So can gaskets, especially a timing cover or intake manifold gasket. Hoses can seep past the connections. If locating this leak is truly difficult, you can add a flurescent dye to the coolant, and then after the next time it leaks look for the dye with a UV light.

    Bookmark   August 1, 2006 at 8:13AM
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My guess is water pump. They typically don't leak while the engine is running and then leak a few drops when you shut it off and then quit. If you drove a long distance it might not have leaked while you were driving. Short trips and more starts and stops and you leak more on a per mile basis. Each time you stop you'd lose a few drops and it adds up if you start and stop a lot.

    Bookmark   August 1, 2006 at 9:54AM
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Worm and John G.: Thanks for the feed-back on this fellas. I don't think its the pump as the weep hole is dry as a bone but I'll keep a close eye on it. The suggestion of putting dye is interesting. I might give that a try. Would a thermostat that sticks closed and then opens late cause an intermitent problem like this??

    Bookmark   August 2, 2006 at 1:22PM
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The thermostat can cause over or under heating, but not any leak...
Use a cooling system pressure pump to test the hoses, radiator, and the cap.
And it can still be the pump(coolant leaking past the shaft seal)..
JohnG has an excellent idea with the dye...

    Bookmark   August 2, 2006 at 5:22PM
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Thanks Earthworm but I'm a bit confused. If the problem is in the water pump wouldn't it leak after each time the car is run? I have driven on several trips, long and short, over a period of weeks with no sign of a leak anywhere. Its a very intermitent problem, at least right now. Maybe I should just replace the water pump to be on the safe side. Thanks for the response to my question guys.

    Bookmark   August 2, 2006 at 8:29PM
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Many water pumps have a drain hole on the bottom side of their housings. Check it to see if it is weeping fluid. You may have to get the vehicle up on ramps or on a lift to get a better view. Sometimes, an inspecion mirror can be used from topside. If you can reach the pump from topside, feel underneath it for the drain hole and wetness.

Water pumps have spring loaded seals. These can hold for long periods of time with minimal seepage, but as the seals wear down near end-of-life, leaking worsens, and the seal may fail catastrophically.

Another source of intermittent leaks is a cracked hose, notable the heater hose. A crack may develop on the inside radius of a tight bend, typically a heater hose that has relaxed and is laying on the engine. It may have a 90 deg bend at the nipple where it attaches to the engine. The crack will leak when the pressure rises in the coolant system, and/or when the hose is momentarily lifted like when the vehicle goes over a bump. You can check this by gently lifting the heater hose, when the engine is hot, and see if it spurts at these bends. Be careful of burns. Sometimes, a wisp of steam issuing from under the hood at a stop light amy be seen, and after parking, the oder of hot raditor fluid may be smelled.

A cracked hose may suddently let go at any time.

    Bookmark   August 3, 2006 at 3:32AM
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Chances are that whatever it is it'll get worse. If it's the water pump, it will get worse. Typically water pump leaks don't put you out of business, especially if you're aware of it and keep plenty of coolant in the system. It's probably not going to just all of a sudden dump all your coolant. It's not usually that hard to find the source of a coolant leak. Antifreeze usually leaves a trail to where it's coming from. Chances are that whatever it is will be fairly easy to find if you keep your eye on it. If it's a hose that runs over the engine you'll see coolant on the engine. If it's only on the ground, look lower.

    Bookmark   August 3, 2006 at 12:23PM
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Water pump seals have been known to fail suddently. One failed on the vehicle of a wife of one of my associates. Where was she went it happened? In the center lane of expressway traffic during the noon rush. Where was he when got her frantic cell phone call? On his way to a meeting with the boss.

So if your water pump begins to leak, don't wait, replace it.

    Bookmark   August 3, 2006 at 6:37PM
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Pressure check the cooling system and use the fluorescent dye/UV light..the leak must then show up; maybe even check with the engine cold and then recheck with the engine hot..
I hate to have a burst hose during rush hour, driving at 60 mph in the center lane..

    Bookmark   August 5, 2006 at 1:45PM
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LEAK FOUND! Thanks to all of your advise, I located the problem. There was a pin hole sized leak in the upper rad hose. I guess when the system reached a certain pressure it would spray a very fine spray of A/F onto the fan blades which blew it every which way. Anyway I replaced both the upper and lower rad hoses using new claimps as well as instaling a new thermostat and gasket while I had things apart. Runs dry and cool now fellas. I cut the bad section of old hose out to see the inside of the hose and it was rotten and close to letting go big time. Fortunate for me that it didn't blow in the middle of no where or on the freeway. Thanks once again to the members on this list. One of the best auto lists on the web I'd say!! Bucky

    Bookmark   August 8, 2006 at 1:16AM
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