6V92TAs ... How much smoke is "too much"?

[Buccaneer]

I know, I know: you need to run them up, get them hot, and then you can cruise at 1100-1500 rpm all day long. And I know that they've been run at 11-1500 for about 50 hrs (well, maybe 100 hrs )without running them up to 2200, and holding, for a while. (I had a bad pressure sender - it read high - and didn't want to risk it till I got that replaced, and I was slow in doing it...)

So, now I get dark gray, not black, smoke. And not a "lot" but enough to notice it. Well, Ok, maybe a lot, but I'm not belching smoke or anything.

I ran them up to 2200 for about 20 minutes both Sat and Sun. And they were still smoking Sunday.

My thinking is to get them hot, and keep them at 21-2200 for about 2 hours (hell, it's only deisel, right?) to really blow them out clean.

Is my thinking sound?

 

[Paul45c]

Assuming you top out around 2300-2350 like most of us, you certainly won't hurt them for a 2 hr. run @ 2100 to see if that cleans them up any.

But I'm sure you know already that you shouldn't have any visible smoke other than at startup, and that for only a very short time.

 

[Genesis]

Shouldn't smoke like that for more than a few minutes. If you're getting gray for more than 5-10 minutes something's not right - it MAY just be buildup, but I wouldn't take the bet.

Can you post a picture?

My guess is that you've got clogged aftercoolers or a turbo problem - that is, not enough airflow.

 

[Avenger]

When is the last time these things saw a tune-up?

 

[MikeP]

The whole smoke thing can be a bit troubling and I think you have to decide on your own whether there is an issue to deal with. Obviously there can be serious issues...or not.

For example, on our 53MY w 8v71Tis: Upon start up (cold, no block heaters) they will smoke considerably. THe smoke will greatly reduce as the engines warm up but they will NEVER stop smoking completely at the dock, regardless of how long the engines run. If you start with the heaters, the smoke level is much less on initial start up but it still smokes at idle. The smoke level from both engines is exactly the same at any RPM. Increasing the no-load RPM at the dock to 1500 and performing no load WOT checks at the dock will not clear the smoke with eng temps at 160 (they won't go above that temp regardless of time spent at the higher RPM.)

Then, moving out of the marina through the harbor at no-wake speed, smoke is not visible. I can smell it but it's not enough to be visible in the boat/air movement. When I get past the no-wake area and increase to full throttle the engines will throw a big cloud of white/blue smoke that will hang over the water like a smoke screen!

However, within 5-10 seconds, all smoke is gone from the exhaust and the boat will not make the slightest wisp of smoke the rest of the day, regardless of the speed. Eng temps at WOT are now 180. Returning to the marina and at idle in the slip - no smoke at all, EVEN THOUGH the eng temp has dropped back to the 160 range!

I used to be concerned about the smoke on start up/idle. Now it doesn't bother me. The boat starts instantly, meets all it's tune-up and WOT throttle specs, and doesn't use a noticeable amount of oil. THe same engine diapers have been under the check valves for 2 full seasons so far and are still not saturated with grunge.

The injectors are clearly overfueling at idle when cold and since the racks/inj height/valve setting, etc are all correct, I suspect a new set would eliminate or dramatically reduce the smoke. Yes, I'd like to see the smoke totally gone but the boat runs so well I'm not currently interested in bothering with it.

So I think the smoke issue has to be considered within the entire picture of the overall engine's operation AND your comfort level with all of it. I've changed my view of all this over the last three years and now believe it's possible to waste a lot or time "chasing smoke" for no really good reason.

Always remember the old definition of a Detroit Diesel:
"A device used to convert fuel oil into noise and smoke"

 

[TedZ]

Sounds like a marginal injector. Running for two hours at 80% of WOT is goofy!! There is no diesel engine problem that requires that strategy.

Ted

 

[Genesis]

Mike, the reason you get smoke on a TI is that the engine has crap for air induction temperature (and thus MASS) control with a SWAC. This is part of why they went to AFTERCoolers - to get better mass airflow control.

Essentially all TI Detroits smoke slightly at idle when not under load. So do other SWAC engines in virtually all cases, and lots of people get pissed about it and try to get manufacturers to "fix it" - to no avail, because its inherent in the lack of decent mass air control. Unavoidable when you can't control the temperature of the liquid side of the cooler.

As for this guy with 92s, gray smoke like that is commonly one of two things - either a bad tip on one or more injectors, or an airflow problem. If there is no evidence of fuel in the water or smoke at idle/low speed, and it only shows up under load, then it is PROBABLY an airflow problem.

An eroded turbine wheel on a turbo will do this as well as restriction (e.g. dirty aftercoolers) on the induction side. Point being, there's more fuel in there than can be burned cleanly.

If the engines start without significant amounts of smoke when cold and clean up quickly it is unlikely that there is a serious compression problem. Besides, I've seen Detroits with BELOW MINIMUM compression numbers that have almost ZERO smoke at speed! While the engines COULD be badly out of tune if they start ok cold and idle ok I doubt it. Possible, but not likely.

By the way, make sure its smoke and not steam. How do you know? Stick a board in the exhaust stream if you can get to it when running and see if it gets blackened. Steam indicates a raw water flow problem and insufficient cooling of the exhaust - that's DANGEROUS and if that's going on you need to fix it immediately because you can either have failures in the exhaust due to excessive heat or, even worse, its possible for the fiberglass components to get LIT.

 

[MikeP]

Good point Karl!

I hadn't thought about the fact that the RW intercoolers are cooling the air regardless of the throttle setting, even when cold air is NOT helpful - like at idle. The aftercoolers can provide warmer than ambiant when the engines need it (idle/low throttle settings) and cool the pressurized under boost conditions.

So, as you noted, they provide much better air temp/mass control than do ICs. Plus, although they are much harder to get to when removal is necessary, they are a more elegant solution than hanging ICs and the associated plumbing on the back of the engine.

 

[Boss Lady]

Detriots are simple devices. The only normal reason for smoke is low compression. As a worn engine comes up to operating temperature, the smoke will clear up, but you are within a few hundred hours of rebuild. A healthy engine will not smoke for very more than a few seconds. You can send your hate mail, but this is the truth. If you your engine is healthy and smokes, then you have a malfunctioning part or system. Ok I am ready to get skewered. LOL

 

[Buccaneer]

OK; so ya'll know more about it than I do - that's why I asked. I'll be checking injectors and aftercoolers now, thank you, and we'll see what's up.

(One of the more interesting aspects of "yachting" is all the education you get in the plumbing, electrical and mechanical arts. Fascinating.)