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Old 04-08-2019, 08:27 PM   #1
DDW
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Odd coolant leak

I came back to the boat after winter storage. Found about 1/2 cup of coolant had dripped from somewhere under the header tank of the Cummins QSB and figured I had a leak somewhere. Cleaned it up and none came back, motored 6 hours, completely dry. Now after sitting in the slip for 5 days, a very small drip in about the same place.

On the QSB, there is a cast tank that the filler cap goes on, bolts to the intake manifold, there are some ins and outs. The leak appears to originate no where near any fitting or freeze plug. And only seems to leak when cold. It is a hard area to see, a green stripe below it on the heat exchanger suggests it has been happening for some time. Any suggestions?
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Old 04-08-2019, 08:42 PM   #2
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DDW,

I used to get a small drip every winter from my QSB. Never lost a drop all summer. Was told it was just from the cold of our Connecticut winters. Since that was the only time it ever happened I just accepted it and moved on.

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Old 04-08-2019, 08:45 PM   #3
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Cold can have some drastic effect on join and fittings, don’t ask how I know

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Old 04-08-2019, 08:57 PM   #4
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Cold leaks are not uncommon. I see it pretty regularly when jacket water heaters fail in cold weather. Once you heat them back up to the normal 100/120* no more leaks. But if it's something out of the norm then you could have a bad o-ring or gasket. I have also seen them get trash stuck in between the o-ring/casting before.
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Old 04-08-2019, 09:36 PM   #5
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My thoughts too. Extreme cold causes o'rings and gaskets to shrink up a bit hence, the drip. Just keep an eye on it, if it gets worse, worry.
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Old 04-09-2019, 01:11 AM   #6
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Hoses shrink when cold. Hoses also extrude over time from under clamps. Go about the whole engine and snug every hose clamp. Could be orings or gaskets, but hit the cheap and easy stuff first (snugged clamps).
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Old 04-09-2019, 02:47 PM   #7
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hahaha everything but water shrinks when cold.
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Old 04-09-2019, 03:21 PM   #8
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hahaha everything but water shrinks when cold.
and sulphur
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Old 04-10-2019, 10:15 AM   #9
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It doesn't take extreme cold, I'm getting a occasional drip at spring PNW temps. I finally began taping blue paper towels under the cast header tank (Cummins calls it the expansion tank but it isn't the same as a coolant recovery tank), waiting a couple of days, then pulling them out to see the wet spots. After a couple of iterations I've chased it back to (I think) the temp sending unit which may be leaking from the wiring seal (not the threads).

One thing that was confounding me is that the tank is sand cast with that rough finish, but the mold parting lines have the flash ground off and are smooth. It looks like the trickle followed one of these smooth flash lines rather than the rough surface. Makes sense, lower surface tension? The tank is painted Cummins white, so the smooth flash lines are already shiny which disguised the wet streak (when looked at with a flashlight and inspection mirror). Diabolical, some of these problems.....
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