Bizarre sudden appearance of oil/soot in cooling water after oil change

[MIke Dempster]

I've got a 1984 Mercruiser 120 system in an 18' "Mercedes" runabout. Engine has been running beautifully. Recently replaced exhaust manifold and riser. Drained oil from engine at the end of the season, but didn't have an oil filter, so left it empty of oil for a week. Did not drain water from block during that week. Weather did not reach below freezing during that week. Put on new oil filter, added 4 qts of 30 weight oil, started up with garden hose on earmuffs, ran really rough, which was a surprise, and I noticed a lot of black oily stuff on the ground where the water came out of the prop hub discharge. After about 5 min of running, the oily discharge was less, and the engine ran fine again. Let it sit overnight, started up again, ran perfectly for about 45 seconds, then started to cough and sputter and again black oily goo was in the discharged water. Photos attached. The black stuff seems more sooty than oily. I removed the thermostat, no oily coating, no water on oil dipstick. What the heck? I'd very much appreciate any ideas!

 

[louc]

That is odd. I wonder if your exhaust elbow is starting to come apart inside…or if a rubber exhaust hose is…or if the exhaust flapper failed and is blocking the exhaust pipe causing too much back pressure…

 

[MIke Dempster]

Hey, thanks so much for your reply, Louc, I hadn't thought of that. Two local folks independently suggested that this is caused by a fuel problem, and that I should clean the carb, because it could be dumping too much fuel into the engine, or that the fuel may be contaminated with water or something. I had just put another 4 ounces of fuel stabilizer into the fuel tank...I say "another" because I couldn't remember if I'd added any stabilizer recently, so there may be a bit too much stabilizer in the fuel. I think the tank holds about 15 gallons of gas. What do you think of that possibility?

 

[Brian3127]

fuel stabilizer does not get rid of the water. if there is water in the fuel tank you have to drain it

 

[MIke Dempster]

So could sooty exhaust be caused by water in the fuel?
Any suggestions for best way to drain fuel tank effectively, if there's no drain plug on the tank?

 

[Brian3127]

take the sending unit off the tank then pump it out. After you do that clean the carb too.
i dont know about water in the fuel giving you sooty exhaust.

 

[makomark]

I'd check the sight tube to see if it has gasoline in it...

 

[kghost]

If the stuff on your finger tips came out of the exhaust then it is NOT the fuel tank.
That crud could not get through the carb or any filters before the carb.

It is from cooling system or exhaust system. Unless a head gasket or Intake gasket has failed allowing that sludge to find its way into the exhaust stream.

What filters if any are in the incoming fuel lines and also include in your answer if there is a filter in the inlet for the carb. Just to confirm you have a normal fuel system to carb.

Is there a water separation filter?
An inline filter?
Filter as part of the fuel pump?
Inlet at carb filter?

 

[MIke Dempster]

take the sending unit off the tank then pump it out. After you do that clean the carb too.
i dont know about water in the fuel giving you sooty exhaust.

What kind of pump is safe and effective for this job?

 

[MIke Dempster]

If the stuff on your finger tips came out of the exhaust then it is NOT the fuel tank.
That crud could not get through the carb or any filters before the carb.

It is from cooling system or exhaust system. Unless a head gasket or Intake gasket has failed allowing that sludge to find its way into the exhaust stream.

What filters if any are in the incoming fuel lines and also include in your answer if there is a filter in the inlet for the carb. Just to confirm you have a normal fuel system to carb.

Is there a water separation filter?
An inline filter?
Filter as part of the fuel pump?
Inlet at carb filter?

I was assuming that the theory of it being a fuel problem is that the black stuff is a result of very poor combustion of the compromised fuel, not that the black stuff itself actually came through the carb.

If the head gasket or intake gasket failed, how would the black stuff appear? Water gets into the combustion chambers and causes poor combustion, I presume?

There is no water separation filter. I am not at the boat today, I'll have to check on those other filters you mentioned tomorrow and report back.

I really appreciate that you've taken the time to help me think this through. You and the others who've weighed in here. Thank you.

 

[MIke Dempster]

I'd check the sight tube to see if it has gasoline in it...

Don't know what the sight tube is. Maybe I don't have one?

 

[MIke Dempster]

Here are photos of the fuel pump and carburetor. Where might a filter be in this system?

 

[kghost]

See image attached and download for your records.

 

[Brian3127]

What kind of pump is safe and effective for this job?

a hand pump is probably the safest.

 

[kghost]

I was assuming that the theory of it being a fuel problem is that the black stuff is a result of very poor combustion of the compromised fuel, not that the black stuff itself actually came through the carb.

If the head gasket or intake gasket failed, how would the black stuff appear? Water gets into the combustion chambers and causes poor combustion, I presume?

There is no water separation filter. I am not at the boat today, I'll have to check on those other filters you mentioned tomorrow and report back.

I really appreciate that you've taken the time to help me think this through. You and the others who've weighed in here. Thank you.

The cooling cavities inside the block accumulate a lot of crud over time.
If you were to ever remove the head and blow out the water jackets/cavities you would be amazed on what comes out of the engine block.

Its Black, ugly and would make you think how does the water circulate with all that stuff in there.

So you say it was running fine.
Then it wasnt.
Possible issues,
1. Water in gas
2. Filter clogging- as you see in my prior post, there are 2 fuel filters you did not know existed.
3. Possible intake/exhaust gasket leak
4. Possible exhaust elbow gasket to exhaust manifold leak
5. Something you did and overlooked to mention it.

Pull one spark plug at a time and look at them. They should be dry, dark grey/brown if normal.

If they are wet or all crudded up then there may be something going on...
If you pull the plugs, take pic of all four and post..

 

[kghost]

One last thought, maybe the points have malfuntioned and simply need cleaning or replacement or regapping.
This can and does happen sometimes after running all season and then sits and collects moisture.

 

[louc]

That, or the choke could be sticking & not opening a fraction of an inch after the engine starts (as it is supposed to) or the carb float is sticking, flooding the engine. It could actually be 2 separate problems (ignition/fuel) + some part of the exhaust system coming apart. Not so likely to both happen at the same time but it is possible.
When I had my cyl heads off 6 years ago to replace, yes the cooling passages of a raw water cooled engine are NASTY. Rusty, cruddy, etc. It literally took my hours to fully clean all 26 cyl head bolt holes/threads (4.3 V6) so that when I installed the reman heads I'd get accurate torque readings. If I put a reman engine in this boat, for sure it will have at least a half closed system.


Yet with the nasty cruddy internal cooling passages, the engine did not have a chronic overheating problem, and when I replaced those old cyl heads, the engine still ran at the temp rating of the thermostat, (160) and never runs hot, the short block is original from 1988.

 

[MIke Dempster]

The cooling cavities inside the block accumulate a lot of crud over time.
If you were to ever remove the head and blow out the water jackets/cavities you would be amazed on what comes out of the engine block.

Its Black, ugly and would make you think how does the water circulate with all that stuff in there.

So you say it was running fine.
Then it wasnt.
Possible issues,
1. Water in gas
2. Filter clogging- as you see in my prior post, there are 2 fuel filters you did not know existed.
3. Possible intake/exhaust gasket leak
4. Possible exhaust elbow gasket to exhaust manifold leak
5. Something you did and overlooked to mention it.

Pull one spark plug at a time and look at them. They should be dry, dark grey/brown if normal.

If they are wet or all crudded up then there may be something going on...
If you pull the plugs, take pic of all four and post..

Ok, here are all four plugs, and one up close. All are black, but not crudded up. So something's been causing it to run rich. Duh, you might say, given what we've seen so far. It's been suggested that blocked fuel filters might contribute to this problem...but wouldn't that incline the thing to run lean, if it could run at all?

In response to your item 5, above, you're right, I did something else I don't usually do when starting this engine, but I don't see how it could've contributed to the problem: Because I was planning to add some Mystery Oil into the carb to fog the engine before shutting it down for the winter, I first removed the spark-arresting air filter. That's all. I noticed what I think is the choke plate partially open, and as the engine was coughing and sputtering and blowing out that black crud, I manually opened the plate all the way, and the engine ran way better. But it's always partially open when starting, so I don't see how anything I did there caused the rough running and spitting out the black crud. It doesn't usually do that when starting.

 

[kghost]

Lack of fuel = lean
Too much Fuel based on your info points to choke.

Maybe the choke stuck closed a bit longer than it should have and thats the issue.
Start engine on hose and let it fully warm up and confirm choke full openes at least most of the way.

If it does not move at all then start there and find out why.

 

[louc]

Those plugs look carbon fouled via too rich fuel mix

 

[MIke Dempster]

Ok, thanks a million to everyone who weighed in here to help me. What a fabulous resource you all are! Don't have time to mess with it for at least the next week, but I'm eager to see what I can do to get this sweet little engine back in the groove!

 

[makomark]

Don't know what the sight tube is. Maybe I don't have one?

looking at all of the pics that have been posted, I'd bet you don't have the standard TYGON sight tube. It looks like it may have been replaced by standard fuel hose (black rubber).... I'd be inclined to check it at the fuel pump end...It would also be wise to replace it with TYGON so you can have the visual inspection capability that was originally supplied...

 

[jimn]

Hey, thanks so much for your reply, Louc, I hadn't thought of that. Two local folks independently suggested that this is caused by a fuel problem, and that I should clean the carb, because it could be dumping too much fuel into the engine, or that the fuel may be contaminated with water or something. I had just put another 4 ounces of fuel stabilizer into the fuel tank...I say "another" because I couldn't remember if I'd added any stabilizer recently, so there may be a bit too much stabilizer in the fuel. I think the tank holds about 15 gallons of gas. What do you think of that possibility?

There's no way fuel should cause that much black gunk.

Before adding anything to the gas, take a fuel sample. If it has been stabilized with anything with dye, you'll see that it doesn't look like fresh gas but I have to ask when 15 gallons EVER needed 4 oz of stabilizer?

What are you using as stabilizer?

Letting the boat sit for a week can't cause the carb to dump gas in that amount- engines sit for years without doing that. I bought a 4 Winns with a 120 in Aug, 2018 and because of a variety of BS that happened between then and this past Summer, I didn't get it on the water until the 5 year anniversary. It sat for 3 years after I winterized it for the second time and rather than take chances, I did it last year after finally being able to run it and adjust shifting/carb/etc. It ran OK last year, but after replacing the spark plugs, it ran great but never did it produce anything like what you're showing. The old plugs were black, but I don't know how long they were in the engine- the previous owner had re-defined 'overheated engine' and I got to fix the problems he caused.

 

[jimn]

I would recommend removing the exhaust elbow, so you can check the inside of the rubber bellows that attaches to the top of the exhaust tube- if it has oily, black gunk but the riser and elbow don't, it's possible that the rubber is breaking down. If the riser and elbow DO have this in them, check your compression and look at the oil- it should be transparent enough that you should be able to see through it if it's in the bottom of a small clear container (if you have a vacuum pump, you should be able to draw enough oil from the dipstick tube).

Did you have the outdrive tilted up for long? Are leaves falling from the trees? Is it possible that leaves entered the prop and rotted (it doesn't take long)? The photo of your finger looks like a blade of grass or a leaf stem is at the upper left- how long was the prop facing upward? Did you remove it to look in?

 

[kghost]

I would recommend removing the exhaust elbow, so you can check the inside of the rubber bellows that attaches to the top of the exhaust tube- if it has oily, black gunk but the riser and elbow don't, it's possible that the rubber is breaking down. If the riser and elbow DO have this in them, check your compression and look at the oil- it should be transparent enough that you should be able to see through it if it's in the bottom of a small clear container (if you have a vacuum pump, you should be able to draw enough oil from the dipstick tube).

Did you have the outdrive tilted up for long? Are leaves falling from the trees? Is it possible that leaves entered the prop and rotted (it doesn't take long)? The photo of your finger looks like a blade of grass or a leaf stem is at the upper left- how long was the prop facing upward? Did you remove it to look in?

At this point there is no need to take apart anything.
Mark raised an excelent point.
If the sight fube is black gas line it should be replaced with a gas approved clear line which can be purchased. The sight tube will show gas if the mechanical fuel pump diaphram ruptures which will fill the line with fuel and dump it into carb.
I have seen this many times!

His boat ran perfectly fine until it sat.

Many unkowns at this point.

But the fact that it starts to run fine after it warms up leads more towards choke at this pount.

 

[jimn]

Lack of fuel = lean
Too much Fuel based on your info points to choke.

Maybe the choke stuck closed a bit longer than it should have and thats the issue.
Start engine on hose and let it fully warm up and confirm choke full openes at least most of the way.

If it does not move at all then start there and find out why.

At this point there is no need to take apart anything.
Mark raised an excelent point.
If the sight fube is black gas line it should be replaced with a gas approved clear line which can be purchased. The sight tube will show gas if the mechanical fuel pump diaphram ruptures which will fill the line with fuel and dump it into carb.
I have seen this many times!

His boat ran perfectly fine until it sat.

Many unkowns at this point.

But the fact that it starts to run fine after it warms up leads more towards choke at this pount.

And if it's like mine, it should have electric choke.

 

[kghost]

And if it's like mine, it should have electric choke.

In his picture it shows an electric choke with insulated heat tube.

 

[louc]

I could be wrong but that looks like the old fashioned Rochester hot air choke. Vacuum inside the choke housing sucks hot air thru that insulated tube which picks up hot air from the hot section of the exhaust manifold. The hot air inside the choke housing then unwinds the thermostatic spring & that opens the choke. Had a similar set up with a 1970 Ford 302 V8 & a Motorcraft (Autolite) 2100 2bbl carb.

 

[kghost]

I could be wrong but that looks like the old fashioned Rochester hot air choke. Vacuum inside the choke housing sucks hot air thru that insulated tube which picks up hot air from the hot section of the exhaust manifold. The hot air inside the choke housing then unwinds the thermostatic spring & that opens the choke. Had a similar set up with a 1970 Ford 302 V8 & a Motorcraft (Autolite) 2100 2bbl carb.

Yes you are correct, That is what happens when you view things from a "SMAHT PHONE"........
Its amazing how these older systems are still functional after all these years.

But It does make a point,
Being that old, Maybe the choke stuck closed a bit longer then normal due to colder temps both air and the house water feeding engine. This could explain the rough running and black sooty smokey exhaust....until it warmed up.

 

[jimn]

In his picture it shows an electric choke with insulated heat tube.

The intake/exhaust manifold looks different from mine, even though his and mine are from 1984. The black tubing and breather tube look fairly new, too- maybe the clear tubing was replaced- mine had deteriorated before I bought the boat.