White smoke on idle

[myoldchev]

SO, we finally had a nice day here today and we took the truck out for a spin. I noticed that it smokes like crazy when it is idling. Rev er up and the smoke disappears. Seems to run fine other than that. It also smells like there is unburned fuel in the exhaust. Is this a mixture issue? Motor is 350 w/ Quadrajet. I'm fairly new to working on these. Any help is greatly appreciated.

[Bishops Trucks]

The white smoke could be a sign that a head gasket is starting to go. Are you sure it is a fuel smell and not a sweet smell (Antifreeze). If it is a fuel smell then you need to lean out your carb, it is running to rich. The engine running rich would have nothing to do with the white smoke. Have you noticed the fluid level in the radiator going down? That is something to keep an eye on.

[chipflyer]

If its an auto trans I would say the vacuum modulator valve on the transmission is leaking. The steel vacuum line that runs from the intake down to the transmisson is hooked to the modulator valve. They rarely fail but when they do engine vacuum pulls tranny fluid up that steel line and the engine burns it and it will really smoke white. If its a manual trans - never mind

Jeff

[Bishops Trucks]

Hey Jeff,
I forgot about that one. I had that happen on both of my '71's.
Dan,
Pull your plugs and see if any of them have a red tent to them, that is if you have an automatic trans.

[myoldchev]

I'm pretty sure it is not coolant. Radiator is always full to the brim. If it is the vacuum modulator on the tranny, would it only smoke on idle or would it be smoking all the time? I will pull a plug and take a look tomorrow. Thanks for the help!!

[IvelDesigns]

correct me if i'm wrong, but don't you have a pretty good chance of hydro-locking your engine if the vacuum modulator fails like this?

i suppose it depends on how much tranny fluid is getting sucked through the line.

[Bishops Trucks]

I have never had any hydro-lock before, not saying it couldn't happen. On my 2-wheel drive when the valve went bad it pushed fluid out of the dipstick tube. On the 4X4 it sucked it into the carb and down into the cylinders causing it to run like sh!t.
Dan,
It could be that the valve is just starting to fail. If this is a 2 wheel drive truck we are talking about, then it is a 15 minute job to replace it. I can't remember the cost of the part but I don't think it was more than $30.00. How long has this been going on? Make sure you get the right one for a T.H. 350 or 400.

[Boog]

White smoke is very often auto tranny fluid being sucked up into the engine. It would show more at idle since engine vacumm is often highest at idle. Strongest vacumm will pull the fluid easier. Pulling the vacumm line off the modulator there should be some fluid drip out of it if it is going bad.
Just in case the smoke is blueish it is motor oil being burned. Worn valve seals and or piston rings.

[chipflyer]

I am pretty sure the modulator valves function is to aid in smooth shifting, the quickest and easyest way to tell if it is leaking is to do the following. With the truck in park and idling disconnect the vacuum line at the carb orr intake and it should stop smoking if the valve is bad, You dont want to drive it like that but you should be able to diagnose the mod valve pretty quick.

Jeff

[cdowns]

well if it sits for awhile you'll get white smoke just burning out the moisture in the engine and exhaust system then theres the fuel blends i know when i lived up north the winter oxygenated fuel blends ALWAYS burned with white smoke smelled too