I was looking under my truck today (while it was idling) and saw saw a big black tube hanging down on the driver side of the engine next to the starter. It was emitting what I think is exhaust. what is this tube, whats its purpose and is it indeed exhaust that I saw?

 

It's the draft tube. It's normal to see a LITTLE vapor from it. It vents off the pressure from the crankcase.

 

its a blow-by tube--you prolly dont want to see very much coming out of this!

 

Thanks for the responses. I guess the only way to moniter itwould be while idling. There weren't a lot of fumes coming out, just enough for me to notice.

 

a buddy of mine somehow tapes a baby food bottle to it to catch all the blow-by. Im not too sure how he does it, so it can still breath, but hes a diesel mechanic, so he must know what hes doing.

-Gary

 

my 97 drips a little oil out of that tube when its parked overnight, maybe a couple drops, is that normal? only oilstains on the driveway are from that tube, pretty good for a truck with 208k on it, the whole bottom of the motor is dry, gotta love that My old 01 ford F250 7.3 leaked from the rear main seal once i got 40k miles on it, my buddies 00 7.3 did the same thing. Good love the cummins.

 

What side of the starter is supposed to be on? Or does it matter? Mine is between the block and starter..

 

mine is between the block and starter as well.

 

To catch the few drops of oil from my blow-by, I cut a clear plastic shampoo tube to about 5". I got a 3/4"x 2" pvc pipe, inserted it so the top was flush to the shampoo tube and hose clamped it next to the blow-by tube. This allows air and oil to flow out the blow-by, the oil gets caught by the tube, then the air makes a U turn out the pvc.

 

As advised earlier, it is for crank case ventilation. If the fumes and slight oil mist is cruddin' up the tranny pan and the surrounding parts in that area(as it was doing on mine) extend the hose out towards the rear of the truck with a 5/8" barbed heater hose coupling and some 5/8" oil resistant hose. Don't forget hose clamps. Carmyne

 

how much blow by is too much blowby?

if it leaking oil through it, and is blowing by a lil pore then usual trucks, does it mean the engine is bad? how bad?

 

You need a blowby tool.
The Cummins blowby orifice tool is simply a tee with one .221" (15/64-in) outlet. Connect one end of the tee to the end of the blowby tube. Put a manometer on last tee outlet. That is your blowby tool. They sell them at Cummins, but I have made my own plenty of times, less than $10. A simple manometer can be made by looping into a 'U' 6 feet of clear tubing with water in it half way. Measure how high the water level rises with a tape measure, multiply it by 2, convert it to LPMs.

Rough conversion is 1"= 27 lpm, add 3 lpm for each one inch (1/2'' of rise in the tube) of water

The reason for multiplying by 2 is that inches of water equals the water rise in the open end of the tube plus the inches the water is pushed down on the engine side of the water tube. For simplicity my numbers below are the measurement of rise only.


Cummins new 5.9 engine numbers are:
63 liters per minute(2.5" water rise) @ 2200rpm,
76 L/Min (3.5" rise) @ 2500rpm
85 L/Min (4.5" rise) @ 2800rpm.

Worn engine that needs rebuilding are roughly double i.e.
126 L/Min(10.5"rise) @ 2200rpm
152 L/Min(14.5"rise) @ 2500rpm
170 L/Min(17"rise) @ 2800 rpm

Beside indicating a compression problem the valves could also be out of adjustment.

Another way (mine), same idea, is to block the blowby tube with a 1/2'' pipe nipple with a cap that has a 15/64 hole drilled in it. Use 3/8'' id looped clear tubing with water in it slipped over the oil dipstick tube. Other tubing end remains open. Use a sharp tipped felt marker to mark the water level with the engine off, have a helper start an already warmed up engine and run the rpms up to 2.2, 2.5 & 2.8k rpms. Mark each water level with the pen, measure the distance from engine off mark then multiply each by 2.

This is all very simple to do, just hard to explain with words.

 

I made a catch bottle with a plastic peanut buttter jar. I drilled a one inch hole in the center of the cap, plus a few small holes so it could breath. I slipped it up the hose, then put a wire tie around the hose to hold the lid in place. Screwed the jar on, then done. Every oil change I drain about a half cup of oil out of it.

 

ok
So while I was doing my vegetable oil conversion I removed the starter to better get to the lift pump, fuel preheater, and other lines. The tube you all are talking about fell out and hit me in the face. I shoved it back, couldn't get it to go, and just didn't worry about it. I figured if it was important they woulda put it on better. I guess now my engine will look like it is leaking oil? Any idea how to get it to go back on (if I can find the hose), maybe I'll put a longer one on to get it toward the rear of the vehicle.
Very enlightening discussion of how to acutally measure blowby. Thanks!

 

I dug up this post. My truck has been showing considerable blow by, pushing the dip stick tube up a few inches and leaking around #1 valve cover. It's only got under 150,000 on it and I'd hate to think it needs a rebuild this soon. I'm hoping its only needing a valve adjustment. The guy I bought it from said he never had that done and he got it at 90,000 miles. I really hope this will fix it. I'm going to do this test as soon as I can get some tubing.