Engine/Transmission (1998.5 - 2002) Blow by question

[John Berger]

What would be considered an excessive amount of blowby? I had a noticeable drop on the dipstick during my last long haul. I figure probably a quart. There are no leaks anywhere except at the blowby tube and it seems there is more there than usual, although it's not excessive. I've heard diesel's will use oil, but what would be an amount that would be something to worry about. I have not had an analysis done in app. 15K. No problems were noticed in the analysis. My truck has 76K on it. A little lesson in blowby and what causes it would be appreciated if someone has the time. TIA



John

 

[me4osu]

Blowby

Is caused by combustion chamber pressure leaking past the piston rings. This is a normal occurance, but within certain volume limitations.



I called Cummins' tech line for what is the actual measurement and specification of excessive blowby for an ISB. He said that is is measured on a dyno under load. The spec. is 18" H2O upstream of an orifice placed between the crankcase and atmosphere. Problem is, he did not know what diameter of orifice, Manifold Pressure, or RPM this reading is taken with. I think GMcLean is a Cummins Mechanic, maybe he would know.



Cummins Southern Plains told me they can't give technical data over the phone.



My employer only buys Cat and Waukesha (big) natural gas engines. So, I can't throw our weight in on this one.



Edit- I PM'd GMcLean to see if he knew.

 

[Vaughn MacKenzie]

Someone posted eons ago about having blowby measured at a Cummins shop. They put the truck on the dyno and hooked up the aparatus and took a measurement.



I would think they could take one at idle since that would eliminate more variables (gearing, tires, temp, and most of all-BOMBs). I've though it would be fun to see if I can get it measured since my truck is close to being in its "prime" at 65K, and use that as a baseline and check it every 100K or so.



Vaughn

 

[me4osu]

In my opinion.....

I don't think you will read much at idle due to vaccuum during idle intake strokes, and the peak firing pressure being low with idle fuel flow and low charge air pressure. Being at full load and RPM puts the engine at its design BMEP (brake mean effective pressure). This is the easiest condition for blow-by measurement through the crankcase vent, due to the increased overall chamber pressure and increased air volume through the engine.

 

[FFutch]

Measure blow-by with a man-ometer,which is a long double barrell tube with liquid in it(either water or mercury). It also has a ruler in inch increments. I would usually hook it up to the blow-by tube with some adapters and rubber hose to the cab,and have someone ride and record readings. This was in class 8 trucks,but I'm sure you can do the same with our trucks,you just need the spec(max. inches of H20)for a B5. 9... Doug

 

[me4osu]

We use digital manometers

These are the best things since sliced bread. Here is the link.

It loads kind of slow.



merical

 

[Wheaties]

John,



Have you considered that it may not be blowby? There have been many more common oil leaks on the Cummins, around the oil pan, through the valve cover, and through the power steering/vacuum pump shaft seal. Many of these paint the bottom of the engine -- I thought my oil was coming straight out of the blowby hose & bottle, but it was the seal on the vacuum pump.



My . 02

Matt

 

[John Berger]

Good info. Thanks. Matt, I am keeping that option open. Problem is, I can't find any noticeable leaks. And, pardon the expression, but I've practically crawled up the truck's a$$ looking for one. I had the oil pan leak, but that stopped after I retorqued the bolts at the back of the oil pan and after I towed my TT over half of Tennesse in April. It's bone dry back there, now.

 

[Big_Daddy_T]

I just had cummins nw check my blow by and it was 10. somin in" at 132k. I missed my 100k tuneup so I had em do it together. They have first class service and techs(unlike the local stealer).

 

[Wheaties]

You're welcome John. I hope that 'option' is what it proves to be. It sounds like you're losing to much oil for it to be a leak and not be noticed.



What other alternatives are there? A turbo seal? A valve seal? Both would feed oil right into the cylinder where it would be burned and out the tail pipe. But you'd be getting more power than you should have If a turbo seal really goes, you'll have a runaway engine.



I really hope it isn't your rings.



Matt

 

[Don M]

The proper size orifice is . 221 inches. Use a tee fitting from the breather tube and at the bottom of the tee drill the . 221 hole in a pipe plug and on the other side of the tee use a number 4 hose.



If using a manometer you will need to convert the inches of water to liters per minute (L/Min).



Newer engines numbers are 63 liters per minute @ 2200rpm, 76 L/Min @ 2500rpm and 85 L/Min @ 2800rpm.



Worn engine numbers are 126 L/Min @ 2200rpm, 152 L/Min @ 2500rpm, and 170 L/Min @ 2800 rpm.





Don~

 

[GeneralMachine]

BLOWBY

HI JOHN, SEEM'S WE ARE IN THE SAME LINE OF WORK FOR I TOO WORK ON STATIONARY CAT ENGINE'S, DIESEL & GAS, AS FOR THE BLOWBY QUESTION, UNLESS YOU CAN FEEL THE PISTON'S PUFFING AT THE OIL FILLER, THE CRANKCASE PRESSURE IS FROM THE MOVEMENT OF THE IN TERNAL PART'S, THAT'S JUST A QUICK CHECK. YOU MAY HAVE A TURBO SEAL FAILING YOU GETING RID OF YOUR OIL. HOPE THIS HELPED. HARV

 

[John Berger]

Let me blow this one by you guys :--) When I noticed the oil leak at the pan, I also noticed a corresponding drop on the dipstick. Not much, maybe half a quart. The leak was probably going on for a couple of months. I noticed it most during long trips, towing or unloaded, it didn't matter. In March I tightened down the oil pan bolts while I was in Virginia. I checked the oil level, didn't add any and then drove around the Bristol area all weekend and then home to Georgia. When I got home, no leak at the oil pan and the oil level had not dropped. I towed the truck all around Tennessee in late April and early May. Total trip mileage - 1863. In late May we went to Charlotte and then to Wisconsin. I checked the oil in Wisconsin, and it was down a bit, but was still right at the top line. I was south of Louisville when I fueled up and checked the oil again and that's when I decided to add the quart of oil. Whatever caused the drop on the dipstick showed up in the last 5000 miles, most of which were significant towing miles. I have not seen a drop in oil level over as many miles when I'm not towing. Is there a connection here?





hwhite - thanks for the complement, but I don't do that type of work. If only I could. My work on engines is limited to my own and any friend willing to be adventurous I don't think it would be my rings, but I'm planning an oil analysis after I get the truck back from the body shop. I'm still under warranty if there is a serious problem.

 

[John Berger]

I received my oil analysis report and all of the numbers look good. Blackstone suggests I run the oil longer between changes. Well at least I know it's not something internal. The numbers are as follows with the first number being my engine and the second being universal averages. I'll do the wear metals to abbreviate this post.



Aluminum 2 4

Chromium 1 2

Iron 24 28

Copper 1 10

Lead 4 4

Tin 1 1

Silicon 3 9



Calcium read 4178 with universal averages being 2491. Since this is an additive and I had 1 quart of makeup within the last 800 miles (which is why I posted this topic in the first place) I figure that is probably the reason for the high reading.



The comments were: All wear read at or better than universal averages show is normal for the type, and metals were in the correct balance to show no faults with mechanical parts inside. As well as your engine is wearing at 76,979 miles, we see no good reason for not running your oil longer. Air and oil filtration look perfect. No harmful contamination found. The TBN was 13. 5, high, and typical of Amsoil.

 

[Mabrown]

My 2002 doesn't use oil, or very little but my concern with blowby is that I can see it! Mainly at night with the headlights on when I stop after a long run I can sometimes see some smoke drifting out. It is not exhaust since it has that smell that you get after changing oil. Does anyone else see their blowby?

 

[John Berger]

I didn't believe mine was using oil, either, but it was down a bit to much on that one stop for fuel in Kentucky. It's peace of mind to have confirmation by analysis. I cleaned my air filter two days ago and had a good look at the turbo. Everything looks good and clean and dry. I'm just wondering if when I checked the oil, there was more in the filter that had not drained back to the oil pan. I have noticed that there are times I'll check the oil and it will appear a bit low. After I let it sit for a couple of hours, the level gradually comes back to what should be normal. I read a post awhile back that suggested that the filter oil may drain back into the oil pan after sitting for a time.



The only time this "leak" was noticed was after towing heavy for a considerable amount of mileage - over 800 miles. I had not towed anywhere but 30 miles up the road and back once between August 2001 and April 2002. My engine should be broken in by now, shouldn't it? The only other explanation that is readily apparent for the oil loss is blowby. This is all fun to talk about, but maybe I really don't have a problem at all.

 

[Tom W]

John, I have a 98 with the blowby vent on the driver side near the fuel filter. I installed a bypass filter and put the return line in the valve cover. For some reason that increased the oil blowby a tremendous amount. I removed and reinstalled the filter several times to verify this so I am positive this is the cause.



I learned yesterday that my Frantz filter should have a restrictor in the filter inlet and perhaps this allowed too much oil to pass thru. I am going to put in a restrictor and reroute the return line to the oil pan.



Tom

 

[A Johnson]

Blow by orifice and spec.

Shortly after the introduction of the ISB, the blowby spec was changed to 10" water max with a . 302 orifice. This is to be taken at rated RPM and load, so a dyno is good but a good hill will work fine. This was a Cummins service Topic so I don't know if the dealers are still using the . 221 orifice as Don M. mentioned.

I don't know the reason for the change in the spec other than I believe the ISB has more blowby than the B series do to a change in the ring pack and piston design. Most cummins engines are measured with the . 302 orifice so it may also have been changed just to have a common procedure/ tooling issue.

Are you running a pack brake? sometimes the blowby is real high under braking conditions do to faulty turbo seals or too much back pressure.

By the way the oil out the breather is an issue Cummins has spent considerable time on and they do have a newer breather that has excess oil drain back to the sump. The bad news is it seems to work on some rigs and not on others. My . 02 for what its worth. A Johnson

 

[John Berger]

No engine braking devices on my rig.

 

[Vaughn MacKenzie]

Here's a good topic from about 20 months ago worth shooting to the top again.



How often do you test your blowby?