Engine/Transmission (1994 - 1998) Blow by check

[GAmes]

I had my engine blow by checked today at at a Cummins shop. It was 4 inches at 3500 rpm, which the tech said was well within parameters, and he was using the odometer mileage which is 295k miles less than actual mileage. It was obvious he was in a hurry to get to the next job and I didn't think to ask him what the parameters are. Of course the FSM doesn't even address the blow by check. Anyone have a chart, or whatever dictates the spread?

 

[cfarrar]

4 inches of what? Water? Mercury? Boogers? 3500 rpm?

 

[HBarlow]

3500 rpm? That exceeds the redline on stock 24 valve or HPCR engines. A larger Cummins engine the tech was probably more accustomed to would be redlined far lower than that. What the heck was this guy doing to your truck? Normally even a corner quick lube facility grease monkey would know better than that.

 

[Redmega06]

I had mine checked at freightliner and I believe that they said it was 12 inches of water. Mine was 8 at idle and 88 before they even got it run up all of the way.

 

[GAmes]

Cummins book said to take it to max rpm. Tech was shocked it went that high, didn't know I have a GSK. I have HD valve springs, so that rpm does no harm. So, anyone have the specs?

 

[GaryOwen]

Got this off another forum and can't confirm accuracy. You multiply the rise on one side of the manometer by 2 to get the total rise. Not sure if your 4" is the total difference or the rise only. If rise only, the total would be 8". Even with an 8" rise, you would be WAY good! Got that engine broke in nicely.



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

 

[Dave M]

I had blowby checked at Cummins about 4 years ago with 120,000 miles on it (I have 230K+ now). I was blowing oil out the blowby tube due to what Cummins guessed was from repeated overfilling of oil. Here is my thread from 4 years ago on that problem:



https://www.turbodieselregister.com...998/127186-oil-blowby-causing-major-leak.html



Here is an exerpt from post #31 of that thread revealing results of that blowby manometer test:

Took the beast to Cummins yesterday and had the blowby test done. It passed. I drove for 150 miles so far with a drip bottle on the blowby tube with a few drops of oil in it. The blowby test was done after driving at freeway speeds for over an hour and they got to it right away so engine was still hot. Results of Blowby test:



1 inch at Idle

8 inch at 2900 RPM (parked... not driven)

Max blowby is specified as 16 inches @ W. O. T.



Cummins Diagnosis: leak possibly caused by overfilling oil. They could be right. I might have not let engine sit long enough before checking oil level... not sure!

 

[HBarlow]

I'm surprised. I didn't know it is considered acceptable to run an unloaded diesel engine at 2900 rpm.

Is the blowby test something that is commonly done in the large displacement diesels used in OTR trucks?

 

[Dave M]

My understanding of why the blowby test is done is to determine whether the rings are bad causing blowby and giving an indication of whether to look further at an engine rebuild or not. It tells how healthy the engine is.

 

[GAmes]

Thanks Dave and Gary, very helpful. However, the numbers for needing rebuild are quadruple in inches but double L/min The tech did say "well within limits", I just didn't ask what they are. That busts the myth that Dodge believes about after market air filters. I put in a K&N stock replacement drop-in at about 11k, an AFE cone at about 110k and the AFE Pro-guard 7 I have now at about 340k. For those who have catch bottles make sure they have more venting area than the id of the breather tube. I have found that the first gasket to blow will probably be the tappet cover gasket. $16 for the gasket, 8 hours of labor to replace.



Harvey; The tech was well versed in big diesels. The shop had to order the correct manometer orifice for my little 5. 9, they had the right ones for the big engines. The orifice probably cost more than the charge for checking the blow-by (less than $30). :-laf