Vent Hose and What Else to Check?

[Bowmanvolfire]

Hello Forum:

Just had a new to me M35A2C 1972 American General dropped off. 12,716 miles with 379 hours. The truck runs down the road, stops, has air assisted steering.

I have zero "big" truck experience. On the passenger side of the motor there appears to be a vent tube. A good amount of "steam" is coming out with the motor running after I ran it up and down the road a few times. The heat index here is 101. Is this normal?

I know to check all of the truck's fluids before I run it anymore. Oil, coolant, brake fluid. Anything else I should look at right away?

Thanks for taking pity.

John
Lakeside City TX

 

[davidb56]

Hello Forum:

Just had a new to me M35A2C 1972 American General dropped off. 12,716 miles with 379 hours. The truck runs down the road, stops, has air assisted steering.

I have zero "big" truck experience. On the passenger side of the motor there appears to be a vent tube. A good amount of "steam" is coming out with the motor running after I ran it up and down the road a few times. The heat index here is 101. Is this normal?

I know to check all of the truck's fluids before I run it anymore. Oil, coolant, brake fluid. Anything else I should look at right away?

Thanks for taking pity.

John
Lakeside City TX

A pic would help, but that sounds like the blow by crankcase vent and it better not be steam.

 

[NDT]

This can be water vapor or oil vapor. If you change the oil and it disappears, it is water vapor. If it remains, it is called “blowby” and it’s a sign of piston rings not sealing well. Again, an oil change with some kind of additives like Lucas can help.

 

[Bowmanvolfire]

This can be water vapor or oil vapor. If you change the oil and it disappears, it is water vapor. If it remains, it is called “blowby” and it’s a sign of piston rings not sealing well. Again, an oil change with some kind of additives like Lucas can help.

Thanks for the answers.

This can be water vapor or oil vapor. If you change the oil and it disappears, it is water vapor. If it remains, it is called “blowby” and it’s a sign of piston rings not sealing well. Again, an oil change with some kind of additives like Lucas can help.

Thanks for the replies. If it is water vapor what is that an indicator of? Photo attached of the vent hose with the truck running.

 

[fleetmech]

That is the crankcase breather. If you follow it, it runs up to the top of the engine and straddles the two valve covers.

I hate to say it, but that looks like quite a lot of vapor coming out. Inspect all you fluids right away and try to determine what is coming out. If its water vapor (steam) you have a massive amount of water in your oil which is not good.

If it is smoke or heavy oil vapor, you either have a completely worn out engine, or possibly large amounts of fuel getting into the oil. I have seen a few engines get loads of fuel into the oil and they will start pouring fuel vapor like that. On a multi, that is usually a blown transfer pump.

Inspect all fluids, especially the oil, right away. Look for the oil to be milky or extremely thin, runny and shiny black. Smell for any scent of raw diesel fuel in the oil. Good oil should be anywhere from light gold, if new, to dark brown or black if its been in there a while.

 

[M37M35]

If it is water vapor what is that an indicator of?

Water or antifreeze in the oil.
Is there drops of water dripping out with the vapor? Is there milky sludge on the underside of the oil fill cap?
Mine did that when it had antifreeze in the oil due to a cracked block.

After the engine has been shut off for awhile you can carefully loosen the oil drain plugs and see if water/antifreeze comes out since it will sink to the bottom of the pan.

 

[Bowmanvolfire]

There is a gelatin like substance on the underside of the cap. So, probably screwed?

 

[eric67camino]

Condensation can form inside an engine due to fluctuations in temperature, relative humidity, etc.. Especially if it sits a lot. When the engine warms up it will "burn off" the condensation. Basically it just boils off the moisture, which comes out as water vapor.

Engines also create a oil vapor mist from heat, moving parts, etc. On more modern engines, this mist us recirculated back into the intake and burned off through the combustion process. Thats the purpose of the PCV (positive crankcase ventilation) system. On the older ones, it was just vented out into the air though the road draft tube, also known as a slobber tube.

The key would be to determine whether it's just the normal venting, or loosing coolant into the oil system.

 

[davidb56]

steal one of your wife's canning jars, run the truck down the street a few times, then set the vent hose end half way into the jar and let it idle a few minutes into it. If you have big problems, you'll have a lot of moisture in the jar. The engine Must be up to temp to do this properly. If there is a some oil and no moisture, then its just tired and I'd run it.

 

[davidb56]

There is a gelatin like substance on the underside of the cap. So, probably screwed?

Not always. the prior owner may have just started it for a few minutes to keep the batteries charged, and didnt bring it up to operating temp for any length of time.

 

[Bowmanvolfire]

Thanks to everyone for the advice. I am going to do the slobber hose in the mason jar today or tomorrow. Oil shows full on the dip stick. Here is the color. Any thoughts seeing this?

 

[NDT]

Thanks to everyone for the advice. I am going to do the slobber hose in the mason jar today or tomorrow. Oil shows full on the dip stick. Here is the color. Any thoughts seeing this?

Looks ok to me.
Until you have “baselined” the oil meaning you know that you have fresh clean moisture free oil in there, don’t worry about the blowby vapor.

 

[Bowmanvolfire]

Not always. the prior owner may have just started it for a few minutes to keep the batteries charged, and didnt bring it up to operating temp for any length of time.

The backstory I have on this truck is that it sat a lot. You nailed it, it probably only ran enough to check the batteries. In the last year or so the truck was barely run at all.

 

[cattlerepairman]

The backstory I have on this truck is that it sat a lot. You nailed it, it probably only ran enough to check the batteries. In the last year or so the truck was barely run at all.

I thought it was a bit of hyperbole when people said, before doing any leak fixes to load up the truck and drive it long and hard.

From my own experience, the above really does take care of a lot of the minor ailments.

I did have an LDT multifuel that always had significant blow-by and oiled the front axle. It ran fine, until it didn't.

I rebuilt an LDS, new rings and all...and it also has a bit of blowby. Go figure.

When warm and idling, you can also take the oil filler cap off and see whether the vapour puffs out rhythmically or merely flows. If it puffs, it is likely connected to one particular bad cylinder.

Sent from my SM-G950W using Tapatalk

 

[Jeepsinker]

"I rebuilt an LDS, new rings and all...and it also has a bit of blowby. Go figure."

I'm glad that thing is still running for you. I remember when you did that overhaul and we were all worried because it still had blowby.

 

[frank8003]

Hello Forum:

Just had a new to me M35A2C 1972 American General dropped off. 12,716 miles with 379 hours. The truck runs down the road, stops, has air assisted steering.

I have zero "big" truck experience. On the passenger side of the motor there appears to be a vent tube. A good amount of "steam" is coming out with the motor running after I ran it up and down the road a few times. The heat index here is 101. Is this normal?

I know to check all of the truck's fluids before I run it anymore. Oil, coolant, brake fluid. Anything else I should look at right away?

Thanks for taking pity.

John
Lakeside City TX

Change the oil and filters, change the fuel filters.
Inspect the drain oil.
The vent tube you see was on all engines many years ago. Slobber tube.

 

[WillWagner]

You said there is goo under the oil filler. Does the engine have plain water or antifreeze in it? The oil looks clean, almost too clean, like fuel. Blow-by vapor is normal, some engines make more than others. If the truck/engine were washed prior to you getting it, could have got bit of wash water in the engine, especially if it was pressure washed. Same if it came from an area that was wet and the engine just started periodically and not worked....I think someone mentioned that above. When the engine is cool/cold, take the filler off the valve cover and look to see if there are water droplets on the cap. Do it slowly and keep the cap level. If so do the taste test. Antifreeze will be sweet if it is normal antifreeze, the kind most older cars used, prestone, autozone, whatever, and bitter if someone has put a modern ELC type in it, no, a small test will not hurt you, look at me, I'm fine! If there is no flavor, other than an oily taste, it is most likely just plain 'ol water. If it is antifreeze, it is getting into the engine in small amounts, hence the non emulsified oil. Could be as simple as a freeze plug in one of the heads having pinhole from running straight water. Either way, I would change the oil and remove the valve overs to clean the top end out after troubleshooting.

Don't panic, go slowly, ask questions here. 1 thing at a time, start by finding out what is in the oil, water or antifreeze, and proceed from there.

 

[cattlerepairman]

@Jeepsinker It was my first multi rebuild/refresh and I remember being super nervous about whether that bucket of bolts would hold together after startup, let alone driving, and whether I had forgotten to torque "that one bolt" to spec....somewhere in there.... lol
It starts as soon as you think of touching the button and runs very strong. Hardly any smoke with the two hole injectors. Could not be happier. The blowby is minimal, just enough to say it has some. Does not guzzle oil, either.

My other ride has an 8V71 and they are both fun in their own way.

 

[ToddJK]

I would agree with most of the advice on here. If the truck barely ran, like any vehicle, moisture will build up in engine, maybe not enough to create any milkiness in the oil, but enough for some steam to be worked out. If you check the radiator and if it has antifreeze in it, if so, keep note of the level or top it off at the base of the neck. I would change the oil, I always add a gallon of Lucas because it does help with dry starts and if you're running normal oil filters and not the spin on anti drain type of filters, it helps. After changing oil, let her run for a while, 20-30 mins, take her out on the road and run her hard for a good half hour or so. When you're back home leave it running and pop the hood open, check everything you can see, look fir leaks, ect, and the crankcase tube. It shouldn't be having steam come out of it or very, very little but there shouldn't be any as the drive and the fresh oil should have taken care of any residual moisture that was in the engine. Shut her down and wait about an hour and check the oil and radiator (as long as the radiator cap is only warm or cool to the touch). Obviously at this time or when it was warm, check the oil fill cap as it was previously mentioned for moisture. I had the same issue when I got my first deuce because it sat so long and had moisture built up in the engine. Same thing happened again when I blew the head gasket and rebuilt the motor over the summer. An oil change and some good hard use took care of that. The deuce I have now will sometimes have some blowby coming out of the slobber tube from the turbo, but that's different but nothing comes out my crankcase breather tube, then again, I drive my deuce everyday as it was my normal car, to work, even to the grocery store. The more you run these trucks the better. They like to run and be ran hard, sitting does more harm than good. However, I wouldn't worry too much about it, just check the fluids often and make note if anything starts disappearing, then there's a potential problem that can hopefully be diagnosed and fixed. Keep us posted, we will try to do our best to help you. Any how, congrats on the newly acquired deuce! By the way, we need more pictures of the truck, we like our trucks, lmao.

 

[ldmack3]

Hate to tag onto an existing post but I have just noticed the same problem. I just replaced the oil pan gasket, oil pump idler gear..see other posts and today ran it for an extended period of time at high idle (brake problem prevents driving it) to get it warmed up. When it got to about 150F I noticed the same fog/smoke coming from my tube. This is the first time I have got it close to temp since doing all the work. There is no sludge on the valve cover cap. The coolant is just water at the moment as I was planning on doing a flush but wanted to get it up to temp once before draining and doing the flush.

In the last year I have only put about 10 miles on it in short trips and never noticed the smoke/vapor until today when it got warmed up. Never does it at idle, never noticed making oil or loosing coolant. I'll do the mason jar thingy but it takes 30-45 minutes at 1200 to 1400 RPM with the radiator blocked to get there. I'm hoping it's just because of all the maintenance I just did and won't do it again. It does have a small head gasket leak between the #1 & 2 cylinders right by the exhaust manifold. I believe it is coolant.

Thoughts?

Another run up to 160F and the smoke greatly dimished.