Smoke/vapor from vent tube.

[Unreal Summit]

I have noticed a big increase in the amount of smoke/vapor from my vent tube, seems to happen since the weather turned hot. Day time or night I can see the vapor coming out around the truck. Runs fine no loss of mpg. Doesn't smoke anymore out of the oil filler hole. Doesn't  use any oil and I only have a drip or two fall into the driveway.  A/c controls, 4x4, and cruise all work as normal.  I did  the moparman mod this winter so it's my first year with it.  Is this normal? Or should I be looking into something?  

Edited May 25, 2019 by Unreal Summit

[Alexio Auditore]

Vacuum leak possibly?

If the leak is small enough, it wont affect your controls for you vents. If it defaults to your defrost vent when the truck is off for a few minutes or longer, then you have a leak somewhere.

 

Weird as it sounds, when it is cold, my truck seems to hold the vacuum better, still leaks though. I know it's in from the part where it goes down to the 4wd.

 

And the mod just might be showing you how smokey it really was in the engine compartment. I can sit in my truck and I'll see some vapor wisping out from under the truck sometimes( with mod).its not too bad though.

[Unreal Summit]

I can see it coming up coming from under my truck and when the wind blows I can really see it! Idk how to post a video on here or I would.  I dont think I lose vacuum after my truck sits. I need to trace all my vacuum lines I guess. 

[Alexio Auditore]

When you get into it in the morning, if the dial is on floors or face but its blowing from defrost vents, that's an easy way to tell

 

(Before you turn your truck on)

Edited May 26, 2019 by Alexio Auditore
Accuracy

[Unreal Summit]

Good idea.  Warm weather  shouldn't make it worse right?

[Alexio Auditore]

The vacuum leak or the vapor blow by? 

 

There shouldn't be a big difference in the blow by coming from your truck whether its warm or cold outside. it could just be more noticable at times, but if it's getting progressively worse, then it's either vacuum or cylinder/ring wear.

 

Somebody correct me if I'm wrong.

 

First just check vacuum. You can get a gauge and test it easily that way. That's what I did, besides the obvious defaulting to defrost. But the gauge will help pin the leak a bit more easily too. I replaced the lines from pump to firewall, disconnected the line to the t case And put the gauge on again. Holds pressure forever. Then reconnected the line to t case, put it on the end where you can add more connections, tested it again, this time losing vacuum. So I know I have a leak between the new line and the 4wd system. 

How many miles are on your rig?

 

[Mopar1973Man]

It can vary from day to day. Some of that is moisture your seeing. As long as you not using oil or blow oil out of the truck your fine. If your concerned pull the injectors and do a compression test. Like one member found out that a single cracked piston can pass a blow by test but would fail a compression test. 

 

So as long as your truck doesn't look like this I think you are safe.

Edited May 26, 2019 by Mopar1973Man

[Tractorman]

@Alexio Auditore is right about checking for a vacuum leak, but using HVAC system for troubleshooting may not be conclusive because there is a check valve in the circuit so the HVAC system can hold vacuum after the engine is shutdown.  There are other vacuum circuits that could be leaking - the transfer case, the CAD unit, and cruise control if you have an automatic transmission.

 

I woud go directly to the vacuum pump, disconnect the vacuum hose and place a cap or plug on the vacuum pump inlet.  Start the engine.  If blow-by decreases, you will know that you have a vacuum leak.  If blow-by remains unchanged, then a vacuum leak is not the source of the problem.

 

- John

Edited May 26, 2019 by Tractorman
Changed "pump outlet" to "pump inlet"

[Bullet]

Hard to tell without seeing it on how much you have coming out.  It's not as easy to add pics or videos as it used to be.

 

I live in the hot south and mine will always smoke a decent amount out my open vent hose when the engine warms up...you can definitely see it well but it's not lingering around the windows or anything like that and I'm not losing oil.  It's always hot down here so it's hard to tell if that has an effect.  I positively do not have a vacuum leak. 

[Tractorman]

2 minutes ago, Bullet said:

I live in the hot south and mine will always smoke a decent amount out my open vent hose when the engine warms up...

 

That makes sense as the air temperature dewpoints in the South are much higher on a daily basis than they are around most of the nation..  The additional moisture from blow-by would take longer to vaporize in the surrounding humid air, so you would see the blow-by evidence linger for a longer period of time..

 

- John

[Bullet]

25 minutes ago, Tractorman said:

 

That makes sense as the air temperature dewpoints in the South are much higher on a daily basis than they are around most of the nation..  The additional moisture from blow-by would take longer to vaporize in the surrounding humid air, so you would see the blow-by evidence linger for a longer period of time..

 

- John

Yes sir...humidity is a killer down here!

[AH64ID]

I thought the vacuum system on these engines was completely independent of crankcase pressure?? 

 

With an external vacuum pump how would a vacuum leak manifest with additional blowby? 

[Mopar1973Man]

Vacuum discharge dumps right into the crankcase. The vacuum pump turns into an air compressor when there is a vacuum leak.

[Unreal Summit]

I got 208,xxx on her right now. I did the vent trick, where I left um on face and when I got in my truck it was blowing out the defrost untill I started my truck. So I undone the main vacuum line and plugged it. Boom no smoke/vapor as all. I think I already found my vacuum leak I just got to go get some more vacuum line. I guess this would make it drip more oil than it used to as well since it pushing more air around. Thanks everyone for your help!

[Mopar1973Man]

Secret... I've not done this yet either but just get Air Brake Line it much stronger and holds up longer without cracking. Just use small pieces of rubber vacuum hose to join the ends.

[Unreal Summit]

Now that's a dang good idea!!! 1/4' air brake line should work well. Thank you!

[Mopar1973Man]

Your welcome. I plan on doing that here soon too. I'm going to super different and not route like factory but get into the hollow of the fender and then tucked up on the cowl properly. I hate the factory route where it's in the middle of everything.

[Unreal Summit]

Yea that was poor design. I might do something like that one day. Good thinking as always!

[Mopar1973Man]

I have seen a repair done another truck where the line got melt by the exhaust heat. I see what the owner did was using Air Brake line and was fairly impressed with the repair but gave me the idea of a full replacement with the air brake line. 

[Unreal Summit]

I got most of mine switched over to air brake line. It still reverts back to defrost after the truck is cut off and sits a few mins. However no more smoke coming from the vent tube and I haven't had a drop of oil from it in a couple of days now. So I'll call that a fix. Thanks y'all.