: Blowby Test

06-03-2009, 05:07 PM
By My Good Friend Bill Flemming

A better way to check engine condition is by a blowby test. This is what Cummins uses and is very simple.

You need a blowby tool. a 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. A simple manometer can be made by looping into a U 6' 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

New engines numbers are;
63 liters per minute(2.5" water rise = 5" of water) @ 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

The valves could also be out of adjustment.

Another way, 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. Use sharp tipped felt marker to mark the water level with the engine off, have someone 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 then multiply each by 2.

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

06-04-2009, 10:36 AM
Thanks, I will do this. One quick question. When you say how many inches of rise, are you talking about only reading one side of the tube?
Normally on a manometer like this you measure the difference in levels from both sides. example if the water goes down 5 inches on one side and up 5 inches on the other, that means you have 10 inches of water. Thanks

06-05-2009, 09:08 PM
thats why you double it

06-06-2009, 08:02 AM
are these numbers for 5.9 litre's of displacment? or 3.9? they should be different

06-24-2009, 11:26 AM
BTTT, I'd also like to know if these are 4bt specs or 6BT. Thanks

MrMechanic Man
06-24-2009, 01:29 PM
I would think these specs only work on the 3.9, but it should be a simple matter of adding half the amount again to get 5.9 specs. The engine displacement is larger therefore the blow-by spec should be higher. (assuming he's talking about the 4bt)

06-24-2009, 03:34 PM
Thanks, but I was asking to avoid making that assumption.

Anyone know the specs for certain?

06-24-2009, 06:51 PM
Those are specs for a 6BT!!!

These are the specs for a 4BT:

45lpm @ 2200rpm
51lpm @ 2500rpm
57lpm @ 2800rpm

90lpm @ 2200
102lpm @ 2500
114lpm @ 2800

Keep in mind these numbers are at 100% Load

06-24-2009, 07:19 PM
Thank you very much for the clarification.

Makes sense that they are under 100% load as well...