OMC 2.5L milky oil after short time

iflyboats

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Well... this is painful.

I recently picked up for $200 a 16' 1980 SeaSwirl with an OMC 400 stringer drive, 2.5L 120HP engine.

All the wooden motor mounts/stringers/etc were rotten out, I have another thread talking about repairing all of that. (Should've quit while I was ahead and not started digging into the subfloor...)

At this point the engine is out of the boat. Before I pulled it, I hooked up water to the engine and got it running. I only ran it for a couple of minutes, it was just a sanity check before continuing on the project.

I noticed that water was seeping out of the exhaust manifold near where the manifold drains are located, looks like there is a crack of some sort there. I didn't put too much thought into it at the time. I had checked the oil before running it, it was at a normal level... unfortunately, I did not think to check it again afterwards.

I've now dumped over a grand into this thing working on the restoration, and my mind came back to the leaking manifold. I went out and checked the oil again after a bit of research and found the dipstick tube nearly full of milky oil.

Is there any chance this is just from the rotted out exhaust manifold? Or is it a pretty sure bet that the block is cracked? Maybe a bad head gasket?

I've seen a couple other threads on this topic and the first step seems to be to pressure test the block... planning on working that out tomorrow. I'm just terrified at how much water got into the oil after just a couple minutes of run time, and I'm afraid that the engine is toast.

Really hoping somebody can console me and say that it's possible it's all from the manifold or head gasket, but I'm highly doubting that at this point....

Appreciate any input here.
 

Scott Danforth

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you over-paid for the OMC motor/Stringer drive/rotten boat combo

a rotten hull will cost you about $3000, the interior which is most likely shot will cost you about $2000. the OMC drive alone will cost you about $1000 in parts for normal maintenance (ball gears, seals, impeller housing and impeller). and much much more if the vertical driveshaft has not been recently replaced.

back to the motor. you need to pressure test the cooling system. its usually never the head gasket. could be the exhaust manifold, could be the block and heads are cracked from improper winterization. the crack in the manifold would be a sure bet indicator of improper winterization. based on that statement alone, I would assume the block and head are both cracked.

however, check

step 1. drain the water jacket
step 2, remove the line from the thermostat housing to the drive (raw water pump), remove the line from the thermostat housing to the exhaust manifold. put a line between the two ports on the thermostat housing that has a gauge and schrader valve and pressure test to 15psi. it should hold forever
step 3, if the block passes, remove the exhaust manifold and perform acetone test.
 

Bondo

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Ayuh,...... Sorry to hear ya dumped so much money into the hull,.....

'bout the only way to salvage it now is to repower it with a Merc, or Volvo driveline,....

Yer block is replaceable, but there's virtually no parts available for the rest of the stringer specific bits,.....
 

iflyboats

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you over-paid for the OMC motor/Stringer drive/rotten boat combo

a rotten hull will cost you about $3000, the interior which is most likely shot will cost you about $2000. the OMC drive alone will cost you about $1000 in parts for normal maintenance (ball gears, seals, impeller housing and impeller). and much much more if the vertical driveshaft has not been recently replaced.

back to the motor. you need to pressure test the cooling system. its usually never the head gasket. could be the exhaust manifold, could be the block and heads are cracked from improper winterization. the crack in the manifold would be a sure bet indicator of improper winterization. based on that statement alone, I would assume the block and head are both cracked.

however, check

step 1. drain the water jacket
step 2, remove the line from the thermostat housing to the drive (raw water pump), remove the line from the thermostat housing to the exhaust manifold. put a line between the two ports on the thermostat housing that has a gauge and schrader valve and pressure test to 15psi. it should hold forever
step 3, if the block passes, remove the exhaust manifold and perform acetone test.
Thanks for all the info. I’ve purchased seals for the lower (it was also freeze cracked at the very tip of the nose... had it welded up), and ball gears/impeller are on the list. I’ve already purchased a replacement used vertical driveshaft due to the original being pitted on the bearing surfaces, is there any other reason those wear out?

I’ll run that pressure test this morning, thanks for the walkthrough on that. The leak in the exhaust manifold is from a casting seam that is quite rusty - not sure if it actually cracked or rusted through. When I got it the manifold drains were out, but I didn’t check to see if there was water in the block which was still plugged.

Wish I knew a bit more about boats before I made the room in my garage... the learn-and-pay-as-you-go approach has caused a good bit of regret.
 

Scott Danforth

Grumpy old guy who plays with boats
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gotta go with new on the vertical driveshaft. the internal splines wear, then strip and leave you stranded needing a tow. 100% of the vertical driveshafts will fail - its a design flaw. the used one you bought will most likely fail soon as well. look at the splines.
 

iflyboats

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gotta go with new on the vertical driveshaft. the internal splines wear, then strip and leave you stranded needing a tow. 100% of the vertical driveshafts will fail - its a design flaw. the used one you bought will most likely fail soon as well. look at the splines.
Dang. And we’re talking the shaft in the lower with the pinion gear on it? Or is this the shaft in the upper housing with the water pump? Haven't opened up the upper yet.
 
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iflyboats

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however, check

step 1. drain the water jacket
step 2, remove the line from the thermostat housing to the drive (raw water pump), remove the line from the thermostat housing to the exhaust manifold. put a line between the two ports on the thermostat housing that has a gauge and schrader valve and pressure test to 15psi. it should hold forever
step 3, if the block passes, remove the exhaust manifold and perform acetone test.

Have my pressure test rig hooked up. So far it's holding solid... had a slight leak through my adapters, once i sealed those up the needle isn't moving. I'll check it again over a period of time and see if it holds. Does this mean my block might be good? or that it needs heat to open up?
 

iflyboats

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Also, looking at the oil on the dipstick again, I noticed it's pretty thin and smells strongly of fuel. I'm starting to wonder if maybe there was just a little bit of water from storage to make it milky but the fuel is what raised the level so much. Any ideas on how to diagnose that issue? I've heard that a bad fuel pump diaphragm could cause that - I guess that's the first place to check?

Edit: pumped out some oil, about a half cup of plain water came out first followed by milky sludge. Maybe not so much fuel... back to the drawing board.
 
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iflyboats

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Found one potential source of water ingress. Took the manifold off and the intake runners are rusted to hell. Boat sat outside uncovered for who knows how long, seems a lot got in through the carb. Also noticed somebody had done a hokey weld job on the underside of the manifold.

Pressure test is still holding rock solid, still not sure how conclusive that test is though. I swear I checked the oil level before running the engine, not sure how I could've missed any sitting water in there so it had to have come in somehow while it was running.

Guess the head is gonna need some work... though now I'm starting to question the lower end if it had standing water in it for who knows how long.
 

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iflyboats

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Got the fuel pump off and disassembled. Definitely wet with fuel on the underside of the diaphragm. No obvious tears but it seems obvious fuel was getting through. Really hoping that the rise in oil level was due to fuel, which seems likely based on the smell of the drained oil.

The water jacket pressure test held solid for 3 hours before I disconnected it. I'm thinking the water was already in the oil before I ran it. Unless there's any other way water could've gotten in while running?

I pulled the head off and there's no obvious signs of cracking or water/rust present in any of the oil galleys, in neither the head nor the block.
 

Scott Danforth

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now acetone test the manifold. if the manifold was cracked on the outside, it may also be cracked on the inside.
 

iflyboats

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now acetone test the manifold. if the manifold was cracked on the outside, it may also be cracked on the inside.
Well, the manifold seems to be holding up. At first I used plain water and it was leaking into the exhaust pretty good, either that or I somehow spilled way more than I thought into it. However I hooked up some compressed air trying to see if I could really get water flowing through, and the leak stopped. I filled it back up with acetone and the exhaust is staying dry... not sure if I plugged the leak with crud with the compressed air or what happened there. But based on the amount of rust in the intake passages, and the fact I got standing water out of the bottom of the sump, is leading me to believe that it was years of rainwater getting into the engine. Really wishing I had changed the oil before that test run, would've prevented a lot of headache.

I pulled the valves out of the head and they're looking much better than I first thought - no rust on any of the valve seats, should be pretty easy to get cleaned up. Figure I'll pull apart the lower end just to see how everything is looking in there - everything I can see from the fuel pump port is spotless, which hopefully continues through the rest of the engine.

Any other way to test for cracks in the block without the heads on it? I've heard of engines passing the pressure test but still mixing water/oil when ran.
 
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Scott Danforth

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I would never trust the manifold myself.

only way to test the block is to pressure test it, or take to a machine shop and mag-particle it.
 

iflyboats

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I would never trust the manifold myself.

only way to test the block is to pressure test it, or take to a machine shop and mag-particle it.
I'm planning on replacing the manifold anyways. The multitude of cracks and weld jobs were enough for me to want to toss it out. Just testing it looking to confirm my hopes on how water got into the engine.

I had pressure tested the water jacket before I pulled the head, and it held a solid 15PSI for 3 hours before I started disassembling. For some reason I still don't feel totally confident in it though.
 

iflyboats

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So I’ve been thinking. Based on the fact the oil was extremely diluted with fuel to the point is was super thin and smelled like a gas tank, coupled with the fact a couple weeks passed between the time I ran the engine and finally checked the oil... I’m thinking I may have had an unlucky combination of a stuck anti-siphon valve and carb float needle that flooded the engine with gas over time. I’m going to clean the carb and reassemble the engine, run it again and see how the oil looks immediately afterwards - should go a lot towards eliminating causes.
 

Scott Danforth

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also check your fuel pump. a failed diaphragm would fill the crank case with fuel
 

iflyboats

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also check your fuel pump. a failed diaphragm would fill the crank case with fuel
I checked out the fuel pump, I don’t believe that’s the cause. Diaphragm looks intact and in good condition, I hooked it up to fuel and blocked the output and pumped it by hand to build up pressure and there were no leaks.
 

Gar & Teako

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Check to see if there is a leak on intake manifold. I've seen the intake rot out on the front right side.
 

iflyboats

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Well, I got the heads and block all cleaned up and back together. Threw the old manifold on for a test run (planning on replacing it, just want to confirm engine is good before shelling out $300). Ran the engine for about a minute with no water to rule out the fuel system - oil still looks exactly as it was after flushing, clean & proper level. (Engine is out of the boat and the outdrive isn't hooked up - not worried about the impeller, even though I also plan on replacing that anyways). I pressurized the water system with a gauge on it while it was running to see if maybe there was some crack that would open up when the engine warmed up a bit, but so far it's still holding pressure.

Really think I'm onto something with the combo of siphon valve & carb float valve both leaking, and the fuel tank siphoning into the crankcase. (Fuel tank is up in the bow of the boat on top of the deck, it's uphill from the engine). I had checked out the siphon valve when I replaced the fuel line and it looked fine, but I'm just guessing some kind of crud got into it. Used to have this problem on old motorcycles, float valve goes bad and fuel fills up the crankcase. Though those didn't have an anti-siphon valve to complicate matters.

It's either that, or maybe I used too much pressure from my garden hose during the original run, and water forced its way past the head gasket or up the head bolt threads due to excessive pressure & old sealant. When I was cleaning up the block for the new head gasket I noticed there were some raised ridges around the coolant passages from years of corrosion, maybe those broke the head gasket seal.

Whole bunch of speculation at this point. Tomorrow I'm taking the engine on a hoist into my driveway and am going to hook up water and run it for a while and see what happens.
 
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