12 Valve Engine and Drivetrain Talk about the 12V engine and drivetrain here. This is for 1994-1998.5 engine and drivetrain discussion only.

blow by

Old 11-06-2006, 04:09 PM
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Exclamation blow by

Today i noticed steam or smoke comming out of my blow by tube. is this something to be very concerned about, or is this normal with 140,000 on a stock ctd.
Old 11-06-2006, 05:02 PM
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normal as long as it is not under alot of pressure. it can be checked with a manometer (sp).
Old 11-06-2006, 06:29 PM
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sorry what is a manometer?
Old 11-06-2006, 06:44 PM
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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 the 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.
Old 11-06-2006, 08:06 PM
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thanks bill i was hoping you would read this, i will try this in the morning,thanks to all who put in advice to these threads if it weren't for you people i would be completely lost with ctd i learn alot from this website
Old 11-08-2006, 06:33 PM
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If you add mod's too your truck do you get more blowby? I noticed after I added my plate and bumped my timing I am getting a little more oil out of my tube.
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