White Smoke On Startup?

[Justin]

1992 W/T 1500 Chevy
4.3L V-6
87,000 miles

After the truck has been siting for awhile (sitting overnight), it blows out a little bit of white smoke out for a few seconds. Doesn't do it any other time though...no smoke when going down the road or when just sitting for a few hours.

Just bought the truck a little while ago, and the day I got it, I changed the oil from whatever was in there to Rotella T 15w40. Truck did not put out the puff of white smoke before this oil change.

Only thing I can think of is this: Leaky intake valve seals (?). Possibly the high detergent level in the Rotella cleared out a bunch of the oil "gunk" on the seals? Because of this, the oil drops slowly onto the pistons, and if sitting for long enough, will result in the smoke.

Think I'm right here??

 

[labman]

I am guessing a slight coolant leak into the composition chamber.
If cleaning out the crud caused any problems, the Auto-RX/ Nutra
users would be in big trouble. Oil produces blue smoke. Too much
fuel produces black smoke. The white coming out your tail pipe is
the same white you see in the sky. If it has a sweet smell to it, it
also has antifreeze in it. I doubt the oil change had anything to do
with it. You just changed it before the truck had a chance to sit
overnight.

I would watch your coolant level very carefully. Also check to see if
the radiator draws coolant back from the overflow as the engine
cools down. Tough to do if you don't have a cap on the radiator
itself. If you have air in the radiator when the engine is cool, it
came from a leak somewhere in the cooling system. An occasional
dose of stop leak could control this problem for a long time.

 

[labman]

Oh yes, if you bought it from a dealer, scream warrenty. Reeplacing head gaskets sucks.

 

[ALS]

It is probably condensation that has formed in the exhaust system over night. After you turn off the engine and the exhaust system cools condensation from the air forms on the metal inside and outside.
When you fire up the engine that water vapor is turned to steam as the exhaust system heats up. Usually it is worse in the winter than the summer. If it is still doing it once the engine warms up then there is a problem. It shouldn't last more than one or two miles or more than 5 minutes. People that drive short trips replace exhaust pieces due to rust far more often than people that drive 20 or 30 miles a day. The condensation is burned completely out of the system during the longer trips

 

[Robbie Alexander]

quote:

---

Originally posted by labman:
. ---snip-Too much
fuel produces black smoke. The white coming out your tail pipe is
the same white you see in the sky. --snip

---

What produces Black crud tha comes out of the tail-pipe?
For thousands of miles, If you back my truck up to the grass (2-3" away), and pump the gas and rev it high, for a minute or two, there usually is a 4-5 inch circle of lightly colored black crud.
When you touch it it feels very slightly oily and wet, if you rub your fingers, it dries and feels
kinda like powder, little sticky, little slick, kinda has no smell, looks like the black stuff in the tailpipe, but I only see a dark layer of crud, and no thick build-up in the pipe. If you mash the GAS real hard -high revs, there is is slight hint of some black smoke but it doesn't really stay, it's almost not there. When you feel near the tail pipe it will feel kinda wet, but I see no water dripping out except the first minute or two in the morning. What's this black stuff?

 

[labman]

Virtually all your gasoline is converted to water vapor and CO2. Even in a well tuned engine with all the smog reduction systems, a little soot and unburned hydrocarbons along with some oil comes out your tail pipe. The cooler the tailpipe, the more condenses and comes out as a liquid. Most of the black is soot. The liquid will be mostly water and maybe a little hydrocarbons and oil. It will also condense on anything cooler the exhaust hits. Small amounts are normal.

 

[MolaKule]

"What produces Black crud that comes out of the tail-pipe?"

This is fuel hydrocarbons for the most part, due to a rich mixture; they have collected in the exhaust system. In my old Suburban with the 350 and Holley Carb., I found that a combination of weak ignition wires/plugs and too rich a setting on the carb was the culprit. If the carb is running rich, put in the hotter range of plugs or decrease the jet sizes.

 

[Robbie Alexander]

quote:

---

Originally posted by MolaKule:
--snip-- I found that a combination of weak ignition wires/plugs and too rich a setting on the carb was the culprit. If the carb is running rich, put in the hotter range of plugs or decrease the jet sizes.

---

Wires are New MSD
Plugs New Factory (use to be NGK coppers)
but I dis-connected my Jacobs and decided
to use up my last set of factory plugs.
Cap and Rotor are new
Original Factory coil though
Ad far as a carb I think this is controlled
from IdleAirControl (orig)-efi 1997
I've only had a lot of BLACK smoke when I was having O2 problems
I've only had White smoke when using cleaner in the intake
All other times, since I recall there has been a light black powder like stuff (like chalk) coat the inside of my pipe and like I say with high revs, comes out the pipe. Just wondering if my gunning the gas causes more of this... I'm always hitting the gas to the floor, doing hard passing, stop and go 30-60 sometimes more times a day. Use about a double dose of fuel conditioner every tank, and the mechanics that replace my plugs, all say they look great, some even mentioned that I'm a little rich but that they'd be proud to have plugs like mine.

And as far ar a hotter plug, How or what do I look for to find this range? How much hotter, next size up?

 

[Rick in PA]

You describe the exact same symptom (white smoke on start-up) as I had from another car some time ago. It was a defective head gasket. Running the motor warms the cooling system, developing pressure in the coolant. If the head gasket is bad, when you shut off the motor, the residual pressure forces a small amount of coolant into the combustion chamber. When you start the motor, the coolant is vaporized and appears at the tail pipe as white smoke.

One of the symptoms is a continual, low level, loss of coolant. Check the radiator.

The troubleshooting procedure for this was interesting. They removed the sparkplugs and pressurized the cooling system with a hand pump. Then they put a small light (a small bulb on a stalk flashlight) into each cylinder. You could see the green coolant pooling on top of one of the cylinders.

Like labman said "scream waranty". If it's got a bum head gasket, it was sold to you that way.

[ September 11, 2003, 10:31 PM: Message edited by: Rick in PA ]