Smoke on startup

[Paladin]

Why does my bus sometimes smoke and sometimes not?

Sometimes I start it and walk back and you might see a grayish haze and smell diesel but nothing prominent but other times like yesterday it smoked a cloud on start up. Usually it's not too bad but on occasion it's a smoker. She sort of loped along for a few seconds on start up before smoothing out the idle as if she really wasn't happy about starting although she did come right to life when I pressed the button.  Might it be related to cooler weather?
 
Is my old motor tired?


-Dave


 

[JackConrad]

Dave,
   Was the ambient temperature colder when it smoked on start-up.  Diesel engines ignite the fuel with heat created by compression. In a cold engine block some of the heat created by compression is absorbed by the engine block and the fuel burn is not complete. This causes some unburned fuel (white smoke) to come out the exhaust until the engine warms up. Colder temps=more/longer smoke.  Jack

[Paladin]

Yep, each time that it's smoked I've noticed that it's cooler than normal. ( Duh, it's getting to be winter!)
On warmer days it really doesn't do much but like yesterday when it was getting chilly it smoked on startup and for about 20 -30 seconds after. After it warmed a little it was fine.


Thanks!

[Hartley]

If it does that and seems to be stumbling or missing for a few seconds, You might
have a cylinder with lower compression on cold starts. Not really something to worry about. Some Detroits stumble until the heat builds up. Just the nature of the beast when they are cold. ( below 50 degrees ) The surging is the idle governor adding fuel to bring the rpm up and then cutting back when it reaches idle rpm. This ususally goes away once warmed up a little. The old 6-71 Inlines will surge, belch,rumble and lope until they are warmed up. ( that was a conditional statement guys! )

Not all engines do these things. Some are better than others and some never exhibit wierd stuff...

dave...

[superpickle]

Its probably Not on daylite saveings time and your Waking it up to Early.. 

your Heartless.. 

[Paladin]

Yep, I'm heartless. She started fine but surged or loped like a race car with a very long duration cam for about 5 seconds until it smoothed out and then it was just the smoke. The smoke cleared up within about half a minute but I'm sure my neighbors loved the cloud and the smell of diesel wafting down the street. 

The other day I had to crank it just a little to get it to start. I had to hold the button for about 4 seconds. It was fairly nippy that day. 


-Dave

[luvrbus]

Paladin,you need to be carefull about starting and idling a DD even on high idle in cold weather it will build up unburnt oil and fuel and one day will sound like its running away when it gets to much buildup, if you can take it and drive to the temperatures reach normal  FWIW

[Hartley]

If ya gotta run it....

My rule is start and run for 30 to 45 minutes or until
the engine is at about 150 degrees or higher. And that's only
if I have a reason to move the bus or am working on something.
Normally I run it until at operating temperature for at least 20 minutes.

The catch is to also let the air cycle a few times through the air dryer.
( blows the condensed gunk out )

Sure it will load up a little but that's better than short starts and stops
and the chance of fuel dilution in the oil and condensation building up.

[Paladin]

That's good info. I wasn't sure just how long I should leave it running. I only needed to move about 3 feet but I left it running for about 15-20 minutes, both times. Once when I backed her up and again when I pulled her forward 15 minutes later. She didn't smoke on the second start up.
Thought it would be good for the old girl since we can't go for a drive right now as much as I'd love to, she's nekked inside with no flooring. Isn't the flooring part of the structural support?

[gus]

If my 671 doesn't start on the first crank when the weather cools I know it is time for the ether.

Ether was meant to be used in this engine and there is a nice little cup on top of the air box to insert ether capsules. Since these are no longer available I just squirt a bit into the cup and she fires right up no matter what the temp.

The big difference in the DD 2-stroke and others is that ether is supposed to go directly into the air box, not the air intake. Also the ether is squirted in, then i walk around to the front and push the starter. It doesn't work as well if the engine is cranked too soon after inserting the ether.

I can only assume that the 8V71 is no different.

[niles500]

*****it smoked on startup and for about 20 -30 seconds after. After it warmed a little it was fine. ****


It sounds like you need a compression check - If you have smoke after the first few seconds (20 to 30 is way too long) you could have bad rings in more than one or more cylinders, one or more bad injector(s) or need a rack adjustment - HTH

[Gary '79 5C]

I just got back from an uneventful 900 mile trip, and yesterdays start up included a bit longer start button 3 sec hold & about 5 - 6 sec of smoke out the back. Ambient was 40 45 deg in northern W Va. I was going to inquire here about same, but again many many friends here are out in front of me.
I was surprised with the smoke, but quickly took in consideration of the temps. I thank the previous responses.

Gary

[bobofthenorth]

Just a heads up on long starts.  And 2-3 seconds is not a "HARD" start - I'm talking probably 10 seconds or longer.  I had some longer starts this spring that I was putting down to colder weather that in hindsight I think were a sign of fuel leakdown.  I changed my check valve this summer (after some REALLY long crank times) and I'm back to "touch the key and away it goes".  And FWIW the fuel leakdown included post start smoke which I don't understand at all but it did and its gone so it has to be connected.

[buswarrior]

Please remember that a coach that is not being driven regularly will exhibit all manner of scary behaviour at start-up that will disappear once it is being driven regularly again.

Few to no mechanics out there has experience dealing with a commercial vehicle that doesn't go out and make money.

We are living in the far reaches of the universe, under conditions that few have travelled before.

Even DD has abandonned us, with the "inactive for 30 days" recommendations for pickling the engine.

Find something more worthy of attention until you are driving in excess of 100 miles every day, with a minium of idling, for a couple of days. Then, if it behaves in strange ways, it is noteworthy and warrents attention.

Treat it like the car. Start it, move it, shut it off. Get roadworthy again ASAP, before you lose ambition to work on it. MCI don't need the floor in them for structure, that is a GM thing. Throw some plywood over the wheels and go for a drive! YAHOO!

happy coaching!
buswarrior