48snowman48

My truck is still pressurizing the crank case to the point where it blows a gallon of oil out every 250 miles or so from the vent tube. I am going to try to schedule a compression test to check the motor. What is a reasonable price to pay for this?
Is there anything else that might be causing this? I have a slight vacuum leak somewhere. I took the line off the side vacuum pump where it has the 90* elbow and plugged it off with a vacuum cap. The blowby did not slow down, but did pick up when I had the line off before I could get the cap on. Was this an effective way to test to see if a vacuum leak was the cause?
I pulled the turbo off to check if a bad seal was the cause of my pressure. Still no difference in blowby.
The head gasket was done just before I got the truck and there are no signs of oil or water contamination.
Any other ideas?

Thanks,
John

gmctd

The vacuum pump is for the HVAC and possibly the brake booster, if you have the large vacuum brake booster unit

If the engine is not missing badly on one cylinder, then the blowby is shared by multiple cylinders - you'll need a compression check to determine that - all cylinders should be within 25psi of all the others, with no cylinder being greater the 50psi from the highest - 'nuther words, one cylinder can be 375psi and another can be 425psi, but better if all are around 400psi

48snowman48

It is hydraboost brakes, but I have been told that the vacuum pump exhausts into the crankcase. The blowby is a steady haze like it is evenly distributed, not just on one cylinder. Thanks for the info on pressures, should it be around 400 then? Thanks.

John

gmctd

That's a good start, John - just make sure that all cylinders are with 25psi of each other - hard starting is main symptom, other than excess blowby, if cylinders are all low

Other causative can be incorrect type crankcase oil - should be Diesel rated CH-CI-CJ - automotive oils are formulated for much less heat, and will result in greater blowby\vaporization in a turbocharged Diesel engine.

48snowman48

The truck gets a fresh gallon of 15w40 rotella every 250 miles or so. You read correctly, thats how much oil I am going through. Having a little trouble locating a compression tester for 12 valves.

gmctd

Make sure the guage is 500psi, suitable for a Diesel engine - here's the procedure:

DO NOT add oil to any cylinder to improve piston ring sealing - this is a heat combustion engine - oil will combust at Diesel compression, at which time the guage parts would disassociate in short order - very exciting to bystanders but very dangerous to any involved party(s) with said guage in their hand

Remove all injectors

Disconnect Inj Pump power wire - dont want any fuel injection

Install pressure plug in one injector hole, crank engine 3-5puffs, stop, read pressure - wait ~5minutes, observing rate of leakdown, if any

Release pressure, proceed to next cylinder, doing same routine, then next, then next, ad infinitum - or, til you run outta cylinders

Compare pressures and leakdown numbers amongst all cylinders - engine could have good pressures, but poor leakdown numbers - that usually points to leaking valves or head gaskets, but can be ring seal

BTW - when I first acquired my truck off the back lot of a back street last ditch car lot, it was using a quart @25mi or so - Dodge wanted 1500bucks to repair it - turned out to be 4 really loose bolts around the timing cover - I pulled the cover, did the dowel pin patch, assembled the cover with new crank seal and a tube of RTV and Voila! - no more oil disappearance.

How does the ground under your truck look, shortly after arrival at any destination?

48snowman48

Very good info. THank you so much for the help. The truck leaks a little, but not much. I believe almost all the oil is coming from the vent tube. It will cloud under the truck, starts up as soon as the truck is started and quits when you shut the truck off. The dowel pin was fixed not too long ago, front case looks to be pretty dry.

John

infidel

Here you go http://www.harborfreight.com/cpi/cta...emnumber=93039

oldblues

hi
just a stab but how is the turbo ?

could a bad seal be blowing into the turbo oil return and into crank case ?

Dshiftff

..........

MarkT

I do not mean to hijack this thread but my motor has 350psi (according to PO) on all 6 but 400 psi or higher is the only number I normally see in past posts. My motor has over 230K miles. I know that the blow by test pressure is the only test Cummins has published numbers. But based upon past experience does 350psi on all 6 indicate a worn motor and a leak down or blow by test is in my immediate future.

I bought my truck 6 weeks ago but have not been able to drive it since I broke my left foot the day before I got it and will be in a cast for at least another 5 weeks= so I do not if it is blowing oil under the truck. It shows no oil past the bell housing right now. It starts great-once I tightened up one injector that way leaking.

gmctd

Fact of the matter is, I couldn't find any numbers for this 17:1 DI engine - the 400 number is for the GM 6.5 IDI engine - I knew it would be lower, and there is a formula for calculating the correct figure, but I can barely do single-digit math, so I was hoping someone would post correct numbers - 350psi sounds more like the correct value - main thing is the numbers be within a specific spread across all cylinders, and the leak-down numbers

If it's missing and leaking back and popping thru the intake or exhaust, low compression and excess leak-down is caused by the valves
- if it's popping thru the crankcase, it's broken rings, or piston(s)
- if it runs smoothly and starts fairly easily and has excess blowby, it's leaking past the rings
- if it runs fairly smoothly, but hard-starting, it's low compression, really leaking past the rings, with excess blowby pressure
- if it's excess vapors, but not much blowby pressure, it's really hot oil, as from excessive volume thru the turbo center section, or plugged coolant side in the engine oil cooler, or wrong oil type - also, normal vapors will be more noticeable in cold weather
- if it's also using a lot of oil, it's time for further checking

Problem is, there's no vacuum on the intake stroke (usually there's Boost pressure), so excessive oil won't be drawn past leaking rings on the intake stroke, as in a gasser (patooie!) engine - that's why you don't see too many Diesels blowing blue smoke from burning crankcase oil sucked into the combustion chamber past leaking rings.

So - how do you determine if an engine is 'blowing' 1 gallon oil out the breather tube every 250 miles?

Here's a quick check -

- fill a bucket with water, place it on the ground near the left front side

- pull the dipstick, place one end of a 5-6foot section (long enuff to easily reach the bucket) of 3/8" clear hose over the end of the dipstick tube, such that it seals

- crank the engine, place the other end of the clear tube in the water - if it doesn't bubble much, try plugging the end of the breather tube - it should bubble more - if not, there's not much blowby pressure

- if it blows serious bubbles from the dipstick with the breather tube open, there may be a problem - as the friendly gynecologist sez: "this bears looking into!"

Next step: compression test

Hammer

With the parts in his signature I'd bet money on a headgasket blown into one of the oil passages with it pushing out the breather assembly so hard......Andy

gmctd

Quite possibly - I was factoring in the new headgasket by the PO - that could have been a desired but not executed fix, or incorrect head-bolt torque - you'll see it pulsing in the water if it's one of anything

MarkT

Thanks- that simple bucket test is one I will try. I bought the truck because all cylinders were the same and it started easy- but when I did a search I kept seeing the 400 number so I had to ask. --Mark