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Old 09-19-2017, 06:28 PM   #1
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Default Oil Leak

So, my recent experience has been that boat engines leak oil and leave a mess in the bilge. I'm trailering the boat so, I can bring it home and swab out the bilge with a old towel and degreaser.

Since buying the boat, she is loosing a lot of oil, roughly a quart in 10 hrs running time and very gentle running, no towing, light loads, low RPM. It's not being burned, there is no smoke at any RPM, no oily smell. But there is a puddle in the bilge, so it's leaking, not being burned. Not leaking around the dipstick fitting, or the oil change fitting.

Has anyone ever used an automotive type "stop leak" type of product. Do they work on a marine engine? Or, is it just a matter of topping it up, and swabbing it out?

Any suggestions would be appreciated. Thanks
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Old 09-19-2017, 07:35 PM   #2
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If you can reach it, check the drain plug to see if it's leaking there. I would rather find the leak and fix it than putting any additives on the oil.
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Old 09-19-2017, 09:25 PM   #3
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Well, it has the Mercruiser quick change oil drain system. The rubber hose has a clip on the end and actually lays up against the motor, so it's not laying in the bilge.

Where that hose attaches down at the oil pan is not leaking. I have wiped it again and again, and no real oil on the rag to speak of.
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Old 09-19-2017, 10:13 PM   #4
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Does it leak oil when the engine is not running? If no it's probably a crank seal.

Can you tell if the leak is near the front or rear of the engine?
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Old 09-20-2017, 02:16 AM   #5
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Just wiping under the engine with a rag, i felt most of the oil was on the front right (starboard) side. I gave it a good long run tonight, and again, very moderate speeds, under 3,000 the whole way.
I'll see what the dipstick looks like tomorrow.
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Old 09-20-2017, 02:52 AM   #6
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What engine do you have? Sounds like it could be the dipstick tube leaking where it enters the oil pan.

Try cleaning the bilge and lay down some paper towels and let it sit for a day or two then look for oil spots and their location.
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Old 09-20-2017, 11:07 AM   #7
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Try tightening the oil pan bolts. Corner bolts should be torqued to 18 ft/lbs, and remaining bolts to 106 in/lbs. That's not very tight, and the bolts can work themselves out with normal vibration. Checking these bolts is fairly easy with a 3.0 engine, but more challenging with 5.0. I'm not sure which engine you have.
You've probably already checked that your oil filter is tight.
I have a wireless borescope that is great for these types of problems. It is compatible with my ipad, has adjustable light, and HD video. I think $40 on amazon.
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Old 09-21-2017, 09:09 PM   #8
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I've got the 4.3 V6. In the short run, i did the paper towels under the engine thing, and we'll see if there are telltales signs.

I'm fairly basic with a wrench, but a check of the oil pan bolts might not be out of the question. I've got a torquewrench around here somewhere. See what happens.
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Old 09-22-2017, 12:53 AM   #9
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Caution you need two different torque wrenches. Ft-lbs for four corner bolts and inch-lbs for all other.
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Old 09-22-2017, 01:54 PM   #10
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thanks for that key piece of info. let's see what happens. in the meantime, I'll keep mopping it up.
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