Bad news boat

[gstock]

I've got a mercruiser 170 4cyl 1986 model. We've had problems for about 3 years with this thing. We just got the ignition system replaced, and also we got the head gasket checked out, we know there is enough compression. They say it is all ok. But every time we go out fishing with this and we idle for around 5 hours or more the thing start to puff out nasty smelling almost yellow smoke, then it stalls and we see a mix of what looks like oil for sure and gas maybe coming out of the lower unit exhaust. Then when we try to start is back up the mixture comes out and it seems to be flooded. Then we have to sit there and wait, because it wont start. It'll run great if we dont idle. Does anyone have any suggestions before we throw more money into it?

 

[JasonJ]

Re: Bad news boat

Get a kicker motor. Those Mercuiser engines are marinized automotive engines, and they are set up to run continuously from mid rpms to redline. Idling any engine under load is hard on it, especially for five hours. The engine, unless it has a thermostat to regulate temperature, doesn't stay hot enough for proper combustion. Yeah, people do it all the time, but they don't understand that they are ruining their engines with improper use. You may need to change the heat range of your spark plugs to compensate for the overly cool combustion chambers, but then you run the risk of problems at cruising to top speeds. Again, if it runs fine any time except after continued idling under load, I would let a kicker do the trolling.<br /><br />BTW, I lived in Madison in the late 70s as a kid, near an arburatum not too far from fish hatchery road. I remember that place had the most horrid winters, tons of snow, ice storms, and in the summer plenty of bad thunderstorms and tornado warnings. I still liked it there though....

 

[Mod2]

Re: Bad news boat

Moving to I/O forum.

 

[Bondo]

Re: Bad news boat

I disagree with jason, All you need is a carb rebuild,+ a Serious carb Tuning, to lean out the low speed circuit.....

 

[akriverrat]

Re: Bad news boat

agree with bondo's post. most marine engines are lowlife pickup motors in a tux. they should idle as well as the truck that tows them.

 

[magster65]

Re: Bad news boat

I think so too, it seems to 'load up' when idling so your low speed/idle circuit and maybe primary jetting is a bit rich. Five hours of idling is a lot, you may want to rev it up once in a while to get some oil spraying around and to 'clean out' your combustion chambers. Some engine components are lubricated by spray or windage. I would never idle around for that long, surely you will suffer some sort of low rpm related failure eventually. I don't think any engine manufacturer on this planet has that kind of use in mind for a gas engine. Good luck.

 

[JasonJ]

Re: Bad news boat

Time for the "why it is bad to load an engine at low RPMS for extended periods" primer. The moving parts of a 4 cycle engine are suspended on a thin film of oil, I am sure evryone knows this. When you load an engine at low rpms, the piston has more resistance against it on its compression and firing stroke. When this occurs, that thin film of oil is momentarily breached, and just for a quick moment, you have metal to metal contact. When an engine is under load at higher rpms, the load is better distributed throughout the rotating cycle and the integrity of the oil film stays intack. Engines have optimum power bands for a reason, none are meant to be used like this. Also, you get more unburned fuel making its way past the rings into the oil because the engine is never at its optimum operating temperature, even with a thermostat. Like I said before If people thing they are meant to be used like this, then go ahead, I think mechanics need more work too. To even say that it is okay to troll all day at idle when everyone knows you are only supposed to idle any engine for minimal times is just bad advise, especialy when the solution is so easy. But hey, good luck and let me know how that rebuild goes in a few years...