3.0L mercury - smoke out of the vent tube

Got parts ;got it running; but I'm getting smoke out of the vent tube on the vale cover.... motor was sitting for a long time is this normal or should I look at a possible cracked head

 

smoke or steam?

A little bit of steam when the oil heats up could be condensation from sitting.
If it's smoke, it's not good.

 

Probably not a cracked head, just leaks from cylinder scratches and/or stuck piston rings or a blown head gasket.
The weak point of this engine is a hotspot between #2 and #3 cylinder that are very close together. Once the gasket starts leaking, erosion damage spreads from that point.

A compression test will provide the answer.

 

Check for functioning crankcase ventilation, which if partly blocked can cause some smoking too.

 

where does the crankcase vent

 

Through the tube that is smoking. Most engines will have something coming out of the breather. In auto installations the breather is usually routed through the PCV valve which is really just a one way valve back into the intake manifold so it is burned with the fuel/air mixture. Older installations just vent it to the atmosphere.

If the motor hasn't run in along time, I would expect alot of "smoke" from the breather until the motor breaks itself back in. Put the end of the tube in a container full of cotton to absorb any solid particles or route the hose near the air intake so the carb/throttle body reingests the fumes.

 

So runnung it until it reseats itself will not harm anything and would this also account for the fuel smell in the oil should i do an oil change and keep doing it until it reseats.Oil is not an odd color

 

Also how i would i find out the model # i got number B779554 off the plate riveted to the block the drive unit # is OC 348383 the transom # is OB853830 carb is 1389-9562(merc) 3.0L inline 4

 

According to:
http://www.sterndrive.info/sterndriveparts/cross_reference_help.html
Merc did not make a 3.0, smallest 4 cylinder is a 3.7L. The number on the plate is smaller than anything listed....perhaps it was made before 1976 and didn't make the list, then maybe it is a 3.0.

It is possible that some gas got past the rings into the oil during your attempts to get it started. It is probably not enough to hurt anything, but won't help either. I would change the oil and filter before I went any further. Use a 5-30 or 5-40 synthetic to help clean out the engine. Make sure the cooling system is working, if on a trailer set up external water flow (muffs or what ever) if in the water put the leg down so the water intake is submerged. Idle until it comes up to operating temp then vary the rpms. Let it run for an hour or so and then check the breather. If it still looks excessive, a compression test is probably next on the list. If you have access to a compression tester, I would do that prior to the break in run, one reading dry and one after oil is squirted into the cylinder, then again after the run to compare data. Let the engine cool to ambient before the second reading.

 

The motor say's 3.0l right on the manifold in both boats i'm going to put the one i'm working on in the glastron sx-17 witch is a 1988 the monte carlo i'm taking the motor out of is 1987 i've looked up parts on a few sites and the OC348383 comes up for a 1987 to 1989 i'm going to put a pic of motor in next post....

 

Here's some pictures of the motor i'm working on and here's a link that say's merc has a 3.0L http://www.marinepartsplus.com/catalog/mercruiser/serial/3.0L_GM_181_I-L4_1987-1989/ 41261
The last picture is the number on the exhaust manifold

 

The engine is a 3.0L, no doubt about it.
Merc doesn't make engines, they buy them from GM. It was once briefly used in a small van, now it still lives on as an industrial engine Vortec 3000L and as 3.0L(X), built in Mexico. The design is from before 1950, no significant changes since then. The original engine had less displacement, 2.8 if memory serves me.

 

My understanding of the 3.0 is it started life as an economy engine in the first generation Chevy II, but wasn't very popular, with the marketing guys who saw Ford with a six in the same class offering. The engine was originally a 153 CID (2.5L) and later punched out to 181 CID. It was used in commercial vehicles and industrial applications.

This engine has seen a fair bit of development since it was first cast. The newer parts for the most part interchange with the older ones, but often not the other way around. The head has seen a good bit of work over the years and even the block is different from the original.

There was a 181 CID that dated back to the 1930's, but it's not the same engine (of course). This engine was designed in the late 50's and was slated for automotive production in 1960 until they elected to replace it with a six. Lots of USPS trucks had them until the 1970's. I used to have a big generator powered with one.

It's a good little engine for what it is, but in marine applications they tend to try to get more out of it then it really likes, so it's noisy and can be problematic if you don't religiously keep after oil changes and routine maintenance.

 

As I said I'm going to be taking this motor out of one boat an putting in another.since I'll be going thru all this I want it to be the best it canand last as long as it can.I've taking off the carb and took it apart and it's a mess need cleaning bad I've ordered new float,inlet seal kit,packingkit,Accelerator pump kit,main jet and gasket set,now I see why it was running rough and not staying running long.since I'm going thru all this should I go ahead and put new exhaust gasket, new head gasket and valve gaskets.I noticed a little bit of rust inside the exhaust manifold that I believe is from sitting so long. what would everyone suggest I soak all the parts i.e.(carb parts) to get a really good cleaning on the I've used the spray can stuff before,but I really want them to get a good cleaning before rebuild also should i soak the manifold to get that little bit of rust out of the inside.I remember cleaning parts as a kid in a shop that had a parts tank but don't remember what the solution was in the tank I really want the parts to be as good as I can get before I reinstall.....also what should the compression be in the cyclinders I'm waiting on a manual and I want to do a compression test today....

 

The manual I ordered is a Seloc repair manual for 1964 to 1991 is there a better manual thats a really good service manaul as in a shop manual...