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Old 09-04-2017, 11:27 PM   #1
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How can this be.

I have a very small oil leak coming from my fresh water pump on one of my Cummins 6BTs, now how can this be, as I would have thought there is only cooling water anywhere near the pump. Its coming from the base of the pump where it bolts onto the block.
Any ideas
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Old 09-04-2017, 11:35 PM   #2
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Your sure it's the FRESH water pump/or leaking on to it from else where?

Raw water pumps bolt into the gear train which is full of circulating oil,and do leak if the seal or gasket is damaged

Cheers Steve
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Old 09-05-2017, 05:54 AM   #3
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Sounds like the raw water pump to me.
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Old 09-05-2017, 06:36 AM   #4
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Originally Posted by CaptSteve53 View Post
Your sure it's the FRESH water pump/or leaking on to it from else where?

Raw water pumps bolt into the gear train which is full of circulating oil,and do leak if the seal or gasket is damaged

Cheers Steve
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Old 09-05-2017, 07:58 AM   #5
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Originally Posted by Sagdito View Post
I have a very small oil leak coming from my fresh water pump on one of my Cummins 6BTs, now how can this be, as I would have thought there is only cooling water anywhere near the pump. Its coming from the base of the pump where it bolts onto the block.
Any ideas
Engine circulating pump is on the front of the block, about in the center. It is driven by a serpentine belt that rides on a smooth cylindrical drive about 2-1/2" in diameter.

The seawater pump is mounted on the timing gear train case, it is gear driven, there are no moving parts visible. It mounts just below the fuel injection pump, held in place with 2 bolts.

The engine pump should not leak oil, there's no oil in contact with any of the internal parts, only engine coolant.

The seawater pump could leak oil if the large (about 4" dia) gasket between the gear case and the pump mounting plate is leaking, there are also shaft seals that keep the oil on the gear side of the housing, they could leak. Case gasket is simple to replace, if the shaft seals are leaking, the pump should probably be rebuilt, or a new one, depending on hours, condition.

I keep a replacement pump ready to go, swap out the whole pump then service the removed pump at convenience. My current pump has over 2000 hrs. Impeller is about due has about 600 hrs.
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Old 09-05-2017, 10:16 AM   #6
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Quote:
Originally Posted by Sagdito View Post
I have a very small oil leak coming from my fresh water pump on one of my Cummins 6BTs, now how can this be, as I would have thought there is only cooling water anywhere near the pump. Its coming from the base of the pump where it bolts onto the block.
Any ideas

If you have oil leaking past the seal on your pump shaft, be aware that if the water pressure exceeds the pressure of the oil, water will be leaking past that seal into the sump, potentially causing a failure that will be much more serious than simply replacement of the seal.
This failure is not uncommon on engines with a gear driven raw water pump, as yours seems to be.
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Old 09-05-2017, 05:18 PM   #7
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Thanks for all the replies but as you can see it is the engine water pump, And I know there should be only water there , but that is where the oil is coming from.
Could it be one of the retaining bolts going into a oil gallery, it's only a very small leak but I would like to stop it.
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Old 09-05-2017, 06:28 PM   #8
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Sagdito, bite the bullet and remove the pump to inspect it and its attachment to the engine. Maybe check tension of the set screws attaching it first, you`ll be undoing them anyway if you remove it.
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Old 09-05-2017, 06:56 PM   #9
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That's pretty clean for being worried about an oil leak!!

Do you run with the belt cover shroud off? The two bolts at the bottom go through and will blow oil if they're removed. Not much, but some. I don't see anything worrisome in those photos, to be honest.

My 6BT also shows oil around the water pump, it's coming from elsewhere, the alternator fan makes it airborne and accumulate in odd places. I would NOT go to the trouble to remove the pump, you'll have to drop the coolant and you still won't learn anything.

Clean everything down well, then look again after running a couple hours. Check for front main seal around the timing cover. That's a common leak point, it can sling from the pulley. The fix is pretty straightforward, remove the balance pulley, pull the timing cover, R&R the seal, replace the timing cover gasket & cover.

I hate oil leaks as well, but my 6BT has 6500 hrs, and has some minor leaks. The cure is far worse than the aggravation of the leak, and I know they're an annoyance and won't develop into anything more than that. So... I fix what can be fixed without tearing the motor down, and live with what remains.

Boatdiesel.com worth the renewal, search there for similar 6BT problems.
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Old 09-05-2017, 07:58 PM   #10
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Looks liike belt dust to me.
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Old 09-05-2017, 08:11 PM   #11
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How about using an inexpensive leak test kit? (Amazon / eBay) Simply put a small amount of the fluorescent dye into the oil, run the engine for a while, then check with the UV flashlight that comes with the kit. The source of the leak should be very obvious.
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