Smoke From Engine Exhaust

[obsessive]

I have a question about our 99' 240DA with the 5.7L TBI engine.

The boat does not smoke directly on startup, but if the enigne is not up to or near operating temperature, and you blip the throttle (taking it up to 2-3K RPM - returning it immediately to idle) I get some light bluish smoke out of the exhaust as the RPM's fall. The smoke smells like unburnt fuel.

It will not do this when warmed up all the way.

Is it because it's running rich because it's not up to operating temp when the throttle is closed quickly - or something else? I'm not too up to speed on the throttle body GM's and how they react to stuff like this during the warmup cycle.

The engine has 430 hours, and the oil is clean - I use about 1/2QT or less during a season.

 

[Hampton]

Sounds like it is running rich during the warm up cycle. I had a 5.7 with a bad thermostat that was running rich because the engine was running too cold. The thermostat was stuck open. I'm not sure if it's completely normal, or if something needs to be fixed/adjusted.

 

[obsessive]

Well, I've got a couple of videos.

The first video is of the smoke directly after revving the engine up. Note the whisp of smoke. It'll hang in the air for a bit and smells like fuel.

The second video is of the engine idiling. When warmer outside (it was 42 degrees this AM) it does not show the 'smoke' at idle (is this just steam from being so cold outside??). This stuff dissapates quickly.

Is this normal?

 

[obsessive]

Any other input?

 

[BonBini]

Great little vid. Shure does look like oil to me. 430 hours on a 99 is 40 some hours a season. 1/2 qt oil if it is leaking makes a hellova mess. Your burning oil like a qt to every 4000 miles in your car. Take a look at what weight oil you are using. 40 weight is still a pretty decient weight to use. Also if you always use the same brand oil, your engine will build up a chemical sludge from it. By rotateing brands you will keep your internals cleaner of this sludge. What one blend leaves behind, anouther blend will clean up. Thats what I think just off the bat anyways. I certainly would'nt go rippen her apart just yet. ...Ron

 

[techmitch]

"Also if you always use the same brand oil, your engine will build up a chemical sludge from it. By rotateing brands you will keep your internals cleaner of this sludge. What one blend leaves behind, anouther blend will clean up." Off the bat huh, sure like to know where you got this info. Maybe its posted on the net some where (please, do tell) so i can follow their instructions and then sue them!

 

[Chris Dauth]

Blue smoke= burning oil,,, Black smoke = rich fuel mix.
I would say your valve stem seals are on the way out.
When you suddenly close the throttle after a rev up, you pull a very high vacuum in the combustion chambers and suck oil down past the valve stem seals.
Seals can be replaced without pulling the cylinder heads.

 

[BarryCF]

I agree with Chris. Valve stem seals. And I wouldn't worry about it until they get far worse.

 

[obsessive]

Ahhh...

That makes sense. I've never had a vehicle with valve stem seals that were worn, so I wasn't sure of the symptom. It makes sense, however, as the engine is still spinning pretty good with the cylinders attempting to pull air past the closed throttle plates. I did, however, think that valve seals would cause a puff when starting the engine after sitting (which the boat doesn't do).

I've run the Mercrusier synthetic oil (25W-40) since I've purchased the boat (three seasons ago - with 370 hours on it at the time). It didn't do it then (or, at least I didn't notice it). I really don't consider 1/2QT per season bad. All engines use some oil as I wouldn't know how the upper cylinders would get lubricated.

As far as replacing the valve stem seals goes and not having to remove the heads. Are you suggesting pressurizing the cylinders with air (with the valves closed) and removing the retainers? Or is there another method? EDIT: After some research, I'm considering the 'rope' method to keep the valves in place.

Barry, what is 'far worse' - smoking under a load?

Eric

 

[BonBini]

Chemical Sludge: Didn't get off the "internet". Came up in a conversation with a chem engineer in the past. Wrenching all my life one becomes a witness to alot of things gone wrong and develops preventive failure skills. Some blends are much worse than others. I wont mention any cause some one may want to sue me too. Something else to ponder over is gas at the pump. If you fill up with the same cheap blend you'll slowly gum up your fuel injectors or carb. A more expensive blend every so often will keep a system cleaner. Or some over the counter fuel system cleaner thats been on the market since Richard Petty. Oh wait, someone blends some of that stuff for you engine oil too. Wonder whats up with that. Anyways, just MHO and 2 cents.

"Burning a qt to 1000 miles": My bad with the math. More like qt to 4000 miles. I base 50 miles to an hour on average on land, and since a boat engine is under heavy load 100 miles per hour. ...Ron

 

[BonBini]

Some synthetic oils in engines: I personaly thought the stuff was great at first. Put a 100% blend in a 4.0 Ford with 75 thou on it. Started using soon after and developed a spark knock I could not figure out. At 110 thou engine started knocking. I found the tops of pistons carbon fouled so bad they were knocking on the head deck. Rings were bad fouled ... Bought brand new 99 Firebird. Switched to 100% synthetic at 500 miles. Ran the sht out of it. Was a qt low at 1500 miles. Found deposits on the spark plugs. Put 10/30 dyno oil in it, still run the sht out of it, at 8,500 miles don't use any. ... Bought a new Ski Doo Mach Z. Ran the sht out of it to break in. Put synthetic injection oil in it. Ran the sht out of it. Found the rave valves stuck big time with deposits. Center cylinder carbon scored. Then came the talk with the chem engineer about flash points and trace deposits. The two stroke needed the mix dialed down. The LS1 Firebird was geting ring flutter above 6k and working like a oil pump. The 4.0 Ford was:huh:. A lot of boat engines at 1000 hours with dyno oil still run decient. The 230 I sold had 1350 on it and was still a 40+ mph boat that didnt smoke like yours.

I personaly dont see what you could be gaining with the synthetic. You change the oil after every season anyways. A straight 40 will be performing like a straight 30 at the end of the season as it breaks down. Multigrades tend to come together ie: 15/40 to a 20/30 as they break down(providing they dont have alot of fuel dilition from poorly sealing cylinders.

Hope that wasnt too much information. ...Ron

 

[obsessive]

I think we're *assuming* that's it's the valve seals. I won't know until I change them. I've run synthetic in some of my vehicles and have run dino oil in others. Didn't notice a positive or negative to either type. The boat still runs 40-42mph and has plenty of power.

I have no idea what oil the previous owner used (dino or synthetic) or what brand/viscosity for the first 370 hours of its life. What I'm unsure of is why it suddenly started instead of gradually (unless I didn't notice it before - but, I chose my screen name for a reason). Regardless, I wish it wasn't happening - whatever is causing it.

 

[BonBini]

Sounds like you might change them this off season. At least then you'll know what youve got in there. Maybe a nice set of alum roller tipped rockers:thumbsup:. Since the rocker covers are off and everthing! ...Ron

 

[obsessive]

Yup, I'm going to get them in the Spring at the boatyard. Is it easy to pull the manifolds off on these? It appears so.

 

[skibum]

Also if you always use the same brand oil, your engine will build up a chemical sludge from it. By rotateing brands you will keep your internals cleaner of this sludge. What one blend leaves behind, anouther blend will clean up. Thats what I think just off the bat anyways. I certainly would'nt go rippen her apart just yet. ...Ron

This is the exact opposite of my experience. Mixing oils causes more sludge than staying with the same oil throughout the life of the engine. Oil manufacturers use additives as part of a formula to give an oil specific properties. They test their oil by itself, meaning that Penzoil doesn't develop their best formula and then test it in an engine with a quart of Valvoline thrown in to see what effect it has on their oil. Mixing oils means that you have no gaurantee that the additives in the different oils are compatible with each other. Stick with one brand so you aren't using your engine as a chemistry lab with unknown ingredients.

 

[BarryCF]

Barry, what is 'far worse' - smoking under a load?

I don't consider smoking during high vacuum conditions to be so bad as long as the engine is developing decent power. Even smoking at cold startup isn't so bad. Some engines are known to have valve stem seal problems with age. Jeep/AMC 360 engines are notorius for this. When it smokes routinely, your oil consumption goes up, or plugs start getting oily would be time for some alarm. Otherwise, if your not to "obsessive" about it I don't believe it will cause any harm. My old Jeep Wagoneer, at 180K, smokes terribly in cold weather for about 5 minutes. Then it's clean as a whistle. No harm. My 2 cents.

 

[BonBini]

This is the exact opposite of my experience. Mixing oils causes more sludge than staying with the same oil throughout the life of the engine. Oil manufacturers use additives as part of a formula to give an oil specific properties. They test their oil by itself, meaning that Penzoil doesn't develop their best formula and then test it in an engine with a quart of Valvoline thrown in to see what effect it has on their oil. Mixing oils means that you have no gaurantee that the additives in the different oils are compatible with each other. Stick with one brand so you aren't using your engine as a chemistry lab with unknown ingredients.

I'm not suporting mixing oils like a trash can party. I do a few complete oil changes of one brand of crude and then try to hit a blend from a different well. I wouldn't be surprised if the oil in a branded qt bottle comes from different refineries from time to time anyways. ...Ron

 

[obsessive]

Amazingly, the only thing I can attribute this issue to was the Sta-bil that I put in. No issues this year what-so-ever, even after the boat being layed up all last year...

 

[Bob & Sue]

I do know one thing for sure bought a new ford fusion a few months ago on the 2nd oil change I was going to have dyno oil put in it to my surprise Ford told me if they put dyno oil in it the warranty would be VOIDED on the spot before driving out. Spoke to one of their mechanics he said the first thing they do with an in warranty engine that has a problem is analyze the oil if its not synthetic the warranty is voided. Ford oil change (synthetic) with filter and tire rotation 34.95 Jiff lube 59.95 go figure.