oil leak/oil dripping from carburator, MCM 140

[dracofan]

I have a 1987 Mercruiser MCM140 181 CID with mercarb.
The engine has been through a complete overhaul, including new lifter, new piston on one cylinder, new powerhead, all gaskets are new, new manifold and
rebuild of carburator. The engine runs well with WOT RPM at 4400 and idle RMP
(in gear) at 700. Spark plugs has been checked and there are no signs
of fouling of the plugs. On WOT the oil pressure gauge is 60 psi.

The oil on idle the oil pressure gauge is fluctuating from 20 - 40 psi, and
the oil consumption has been excessive with oil floating around in the bilge.
There are oil dripping from the vent house from top cover and flame arrestor, and there are oil floating around the vent cover , manifold top and carburator gasket.

It seems to me that the main cause is to much oil been vented out from the crankcase and into the flamearrestor.

Any comments?

 

[Don S]

Re: oil leak/oil dripping from carburator, MCM 140

First step is a compression test. Follow the steps (all the way thru) in this Mercruiser service bulletin.

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[dracofan]

Re: oil leak/oil dripping from carburator, MCM 140

Hi,

Thanks for the update.

Compression is fine, vary from 142 to 151 PSI, should be within limits.
Vacuum is also fine, steady at idle.
Based on your update, you expect to high crankcase pressure to be a possible cause?

Cheers,

Inge

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

Definitely sounds like PCV issue. Is oil being forced out of the dipstick tube at all? - sounds like it's obviously coming from the valve cover breather/vent tube to flame arrestor. Check the PCV valve for proper operation (maybe attached to a poor vacuum source?). Obviously if the rings do have excessive blow-by the PCV process could be over-run etc..

 

[JustJason]

Re: oil leak/oil dripping from carburator, MCM 140

no such thing as a pcv valve in a boat. and you shouldn't have one.
just curious, how did the plugs look when you took them out.... did they have any/much oil on them?

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

no such thing as a pcv valve in a boat. and you shouldn't have one.

Hmmm,
I believe both Merc and Volvo use/have used them. I've had both.

- Out of curiosity, why do you state: "and you shouldn't have one"?

Cheers

 

[bruceb58]

Re: oil leak/oil dripping from carburator, MCM 140

Some of the newer engines have them but not a 1987.

 

[chiefalen]

Re: oil leak/oil dripping from carburator, MCM 140

Just curious did you overflow the crankcase. You put too mush oil in?

Lets try the obvious first.

Check the dipstick please. Smell it also. What do you smell?

 

[mthieme]

Re: oil leak/oil dripping from carburator, MCM 140

Sounds very much like crankcase pressure to me.
Now, where is the blowby coming from?
Did you put the engine together or someone else?

 

[stu01]

Re: oil leak/oil dripping from carburator, MCM 140

1. engine overfilled w/ oil?

unless your on a trailer, and put a bubble level on the valve cover, front to back, side to side, it's going to be difficult to get a proper reading. other than draining and refilling with the recommended amount (number of quarts).

2. ignition timing. who set it, after rebuild?
and after breakin, was it rechecked?

too much advance will produce crankcase pressure.
too much retard will produce crankcase presure.

my "89 3.0 has a pcv valve!!!!!!!!!!!

 

[Don S]

Re: oil leak/oil dripping from carburator, MCM 140

my "89 3.0 has a pcv valve!!!!!!!!!!!

It shouldn't have. Merc only used a plastic hose connection in the valve cover, the newer design valve cover had the connector cast onto the top of the valve cover.
It's very possible the rebuilder left the baffle box off the breather hole inside the valve cover.

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

Obviously the OP has not responded yet this thread continues to reference PCV valves etc. I've been a mechanic for, well lets just say numerous decades. Built, rebuilt, raced, you name it more engines than I can sometimes remember. I can't think of one application that did not have a PCV system - it's a must for combustion engines.

PCV - Positive Crankcase Ventilation

Sure some of the older engines and some race applications just "vented" the valve covers yet that in itself is a PCV system. These however tended to get quite messy over time.

Bottom line, I can't imagine any engine newer than late 70s's/early 80's that did not utilize some form of a "valve" attached/plumped to a manifold vacuum source. I understand boats many times use different designs yet if the valve cover has a hose going to it that is attached to a vacuum source, there will be some form of a valve, small orifice etc. to regulate pressure/vacuum.

As stated, we have yet to hear back from the OP, but if he does have oil being "forced" up and out of the breather tube, it's a PCV issue. That makes it quite obvious that either the PCV system isn't working properly or he has blow-by to a degree that it is overcoming the PCV system. If a baffle is missing in the valve cover-to-vent-tube, that could result in some oil being pulled up but given the description/amount he stated, I would doubt that is the only root cause of his issue.

1. Too much blow-by (bad rings, gaskets etc)
2. PCV "system" not working properly
3. PCV valve ("etc") connected to wrong type or inadequate vacuum source
4. Valve cover baffles missing on breather
5. A combination of any or all of the above...


Cheers

 

[Don S]

Re: oil leak/oil dripping from carburator, MCM 140

I've been a mechanic for, well lets just say numerous decades. Built, rebuilt, raced, you name it more engines than I can sometimes remember. I can't think of one application that did not have a PCV system - it's a must for combustion engines.

I've been a MARINE/BOAT MECHANIC for decades also, and they all do not have PCV valves. It's a boat thing. And the OP's motor should not have one.

 

[JustJason]

Re: oil leak/oil dripping from carburator, MCM 140

I can't imagine any engine newer than late 70s's/early 80's that did not utilize some form of a "valve" attached/plumped to a manifold vacuum source.

That's what i've been trying to say..... Except for the very newest, 8.1 Horizons etc....99% of boat motors do not use a pcv valve... it's just an elbow.

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

^^^And that "elbow" is called the PCV valve..... I've got several boat tech manuals and all reference PCV valves. Both with pictures of "elbow" style and the "rattle" type as many would describe them.


I cant claim to be a boat mech for all of my years yet all 4 of my boats have had one. Even the little 4 cyl merc we had back in the early 70's. Even my current Cobalt, and it's not a big block either. All -from the factory.
I find it hard to believe this is even a discussion.

Not all are "valves" in the physical sense yet if plumbed to a vacuum source its not just an elbow. Many are actually built into the valve cover now days. It's an orifice of applicable size as to not decrease vacuum in the engine yet sufficient for proper PCV system ops.

Call it semantics yet its not just an open vacuum source plumbed into the valve cover.... Now, if it isn't connected to engine vacuum then no, there wont be any valve, small orifice or whatever boat mechs want to call it.

Call it a case of agree to disagree but PCV systems are not rocket science. If it utilizes engine vacuum, it will have a valve of sorts to regulate that vacuum. The engine may be in a boat but it's still a combustion engine requiring PCV.

Cheers

 

[Don S]

Re: oil leak/oil dripping from carburator, MCM 140

If it utilizes engine vacuum, it will have a valve of sorts to regulate that vacuum. The engine may be in a boat but it's still a combustion engine requiring PCV.

The OP's engine DOES NOT have a PCV valve, and stu01's shouldn't have. Doesn't mean some unknowing person didn't stick one in the hole.
They are also not hooked up to vacuum. The hose that goes from the valve cover is aimed at the flame aresstor where the fumes are drawn into the carb. It is not sealed or anything, just stuck on a piece of metal attached to the top of the flame arrestor.
You can say that they MUST HAVE a PCV valve all day, but the fact is, they don't, deal with it.

 

[mkast]

Re: oil leak/oil dripping from carburator, MCM 140

it will have a valve of sorts to regulate that vacuum. The engine may be in a boat but it's still a combustion engine requiring PCV.

Cheers

Because a hose is routed from the valve cover to the spark arrestor doesn't mean the engine is equipped with a PVC system.
Most marine engines aren't equipped with power assisted brakes, therefore, no vacuum outlets.
If you take a look at what you think is a PCV valve on your boat engine, it's hollow, from the factory.
If it's hollow, how can it work as a valve?
A PCV system doesn't regulate vacuum. Throttle position dictates how much vacuum is generated.
A buildup of crankcase pressure over comes spring pressure in an automotive style PCV valve, that's the rattle you hear when you shake it. Vacuum is an easy source to move crankcase pressure to the intake. On a boat, the vacuum is generated from the carburetor throat.
Getting back to the post, how many hours on this engine rebuild? Very common to have oil slipping passed the rings until they seat.

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

You can say that they MUST HAVE a PCV valve all day, but the fact is, they don't, deal with it.

Never said they "must have a valve". I said a combustion engine must/should have a PCV system. "V" in PCV doesn't stand for "valve", it stands for "ventilation".

Mkast - The breather hose from valve cover to flame arrester is the "PCV system". -I mentioned this in a previous post. That breather hose may be the only component of the system or act in conjunction with another "device" - of which is normally attached to a vacuum source.

I'm a new guy on the block yet please attempt to read my posts and comprehend what I am actually saying. It's pretty obvious the OP has crankcase "pressure" issues - either coming from engine mechanical issues or PCV "system" issues. This entire little debate started with me asking the question (of which has yet to be answered), "why shouldn't a boat have a PCV system or better yet a "valve" etc"?? Of course I knew the answer yet was being polite to see what the resident experts were so adamant about.

I've been around boats all my life and the only one I have worked on that did not have a PCV system utilizing a vacuum source was a 56 Chris-Craft... I never said they all had to utilize vacuum and/or a "valve", but know for a fact that a great number do, including mine mkast. I've got no doubts thus have nothing to "deal with".

As for this thread/OP - given the scenario, just ensure whatever PCV "system" your engine has, (and you know since you mentioned it in post 3), make sure it is intact and is functioning properly.
I would love to hear about your outcome dracofan.

Respectfully

 

[mkast]

Re: oil leak/oil dripping from carburator, MCM 140

It's called Crankcase Ventilation.
The "Positive" wasn't added until the valve was installed, no valve...
This ranks up there with calling a sterndrive a "LEG".

 

[KJSmitty]

Re: oil leak/oil dripping from carburator, MCM 140

It's called Crankcase Ventilation.
The "Positive" wasn't added until the valve was installed, no valve...
This ranks up there with calling a sterndrive a "LEG".

You're killing me mkast

However you are right - the "P" in PCV is synonymous with "one-way" travel of crankcase combustionables to the intake. An actual PCV valve facilitates that one-way travel. However, just having a breather tube attached to the flame arrester facilitates crankcase combustionable air back to the manifold vs atmosphere (positive/one-way back to the combustion chamber). A pure "CV" system is one where all you would have is a breather cap/filter or vent tube venting directly into the atmosphere. Many times this was vented directly out through a scavenge system on the exhaust - much like the 56 Chris Craft I spoke of above.

- At least now I know why old timers called their twin engine boat "Two leg'ed".......