LB7 Duramax fuel in oil

[eric67camino]

The truck:
01 Chevy 2500HD CCSB 4x4
LB7 Duramax
407k miles

The history:
Had it for about 100k miles
Injectors replaced 1 1/2 years, 20k or so miles ago
Headgaskets done a year ago (did new, updated headgaskets and headbolts, new belt, new water pump, oil filter/cooler interface gaskets while there)

The problem:
Fuel in oil

The conditions:
Changed oil a week or two ago.
Last night, leaving work, truck idled rough.
Noticed oil pressure lower than normal (estimate typically 60-70 when at cold idle, 35-40 at hot idle)
Was at about 20 at cold idle, around 10-12 at warm idle.
Got it to the house, drained oil, got about 4 gallons diesel/oil mix out of it.
Replaced oil, pressures back to normal-ish.
Ran to town for supplies (probably 40 miles round trip), pressures began to drop again
Got to the house, walked away for a while (very not happy), came back later and noticed fuel dripping out and a puddle in the gravel.
Appeared to be leaking around front and rear mains and possibly oil pan gasket.
Drained approximately 4-4 1/2 gallons of diesel/oil mix.

The theories:
Bad injectors - don't think so because they are fairly new, and it only runs rough after getting way over full. Thinking maybe low oil pressure and thin oil causing lifters to not pump up, which leads to running condition
Broken return line, loose return line bolt, bad return line banjo washer - since it runs fine initially, thinking that the leak is on the return side of the fuel circuit.

I'm open to suggestions. (Preferably ones that are easy fixes, as all of my ideas are going to be labor intensive. Haha.) Has anyone seen this before?

 

[sweetk30]

buddy has a 03 he had to do injectors and hard lines on for this . once torn down found water had gone down hard lines threw rubber plugs and sat on tappered seat for line to injector and rust pitted them to the point they started bleading off and leaking fuel in crank case . he didnt know it and drove it 550 miles home and then found it . didnt hurt it at all but did rinse the sh!t out of the crank case . took a few weeks for the oil to go back to diesel level black . this was a few years ago now and she is still running strong .

 

[eric67camino]

I replaced the injectors, but had to cheap out and reuse the lines.

You thinking the lines leaking before the injectors?

 

[centexk5]

Had the crossover tubes in my Cummins get slightly kicked and leaked fuel in the crankcase. Enough that a wot run would spew oil everywhere. Was changing oil every 100 miles. That engine was spotless inside hahaha. The under carriage was so coated in oil it wouldn’t have rusted sitting with the Titanic.

 

[max 02]

The truck:
01 Chevy 2500HD CCSB 4x4
LB7 Duramax
407k miles

The history:
Had it for about 100k miles
Injectors replaced 1 1/2 years, 20k or so miles ago
Headgaskets done a year ago (did new, updated headgaskets and headbolts, new belt, new water pump, oil filter/cooler interface gaskets while there)

The problem:
Fuel in oil

The conditions:
Changed oil a week or two ago.
Last night, leaving work, truck idled rough.
Noticed oil pressure lower than normal (estimate typically 60-70 when at cold idle, 35-40 at hot idle)
Was at about 20 at cold idle, around 10-12 at warm idle.
Got it to the house, drained oil, got about 4 gallons diesel/oil mix out of it.
Replaced oil, pressures back to normal-ish.
Ran to town for supplies (probably 40 miles round trip), pressures began to drop again
Got to the house, walked away for a while (very not happy), came back later and noticed fuel dripping out and a puddle in the gravel.
Appeared to be leaking around front and rear mains and possibly oil pan gasket.
Drained approximately 4-4 1/2 gallons of diesel/oil mix.

The theories:
Bad injectors - don't think so because they are fairly new, and it only runs rough after getting way over full. Thinking maybe low oil pressure and thin oil causing lifters to not pump up, which leads to running condition
Broken return line, loose return line bolt, bad return line banjo washer - since it runs fine initially, thinking that the leak is on the return side of the fuel circuit.

I'm open to suggestions. (Preferably ones that are easy fixes, as all of my ideas are going to be labor intensive. Haha.) Has anyone seen this before?

All your theories are correct, unfortunately. It could be supper cheep fix but I’m not sure how to diagnose say a leaking return line even with the top VCs off.

 

[eric67camino]

All your theories are correct, unfortunately. It could be supper cheep fix but I’m not sure how to diagnose say a leaking return line even with the top VCs off.

Thats what I'm afraid of. Looks like 10 bucks in parts, but 10 hrs labor to get there.

Not a huge deal for me to do it. Just on a time crunch. Have a trip coming up in a week and a half and need the truck. Might have to break down and pay someone to do it.

 

[max 02]

Thats what I'm afraid of. Looks like 10 bucks in parts, but 10 hrs labor to get there.

Not a huge deal for me to do it. Just on a time crunch. Have a trip coming up in a week and a half and need the truck. Might have to break down and pay someone to do it.

Some smart Duramax guys on here hopefully someone will see this and give you a idea or two.

 

[eric67camino]

Alright folks. After way too long, we have an answer. It's busy season, so I've been working 6 days a week since this happened. Anyways, I figured I would post an update for those who contributed.

I was running short on time before I had to leave for Snake Hunt, so I just did the replacement of all of the return line banjo washers on the passenger side, refilled with oil and tried it again. Same result, overfill with fuel/oil. Had to borrow a truck for the trip. Of course, I have been working 10 hr days, 6 days a week since so progress on the other side had been slow. Finally got it all the way down today.

For those not familiar, the lb7 has 2 intake and 2 exhaust valves, but only one rocker arm for intake and one for the exhaust. They accomplished this by using a bridge plate over the stems of the two exhaust valves and the rocker arm pushes on the middle of the bridge plate.

So it seems that I did not have the bridge plate on the exhaust valves fully seated on the rear most cylinder on the driver's side. And now, a year later, it finally caused an issue. When I got it disassembled, I found the bridge plate pushing on the spring plate, not the valve stem on the lower most exhaust valve. This one is the one closest to the return line. The spring was being pushed on funny, apparently enough to Bush over and break the return line. That's where the leak was from.

Issue now is that one of the valve keepers is missing. Using the glow plug hole for access, I used a fitting from a compression testing tool to put air to the cylinder. This keeps the valve in place while removing the spring. Valve appears to be fine, moves easily, not bent. Got very lucky.

Unfortunately, the keepers that the parts store got me were the wrong size, so I was unable to reinstall today.

 

[max 02]

Alright folks. After way too long, we have an answer. It's busy season, so I've been working 6 days a week since this happened. Anyways, I figured I would post an update for those who contributed.

I was running short on time before I had to leave for Snake Hunt, so I just did the replacement of all of the return line banjo washers on the passenger side, refilled with oil and tried it again. Same result, overfill with fuel/oil. Had to borrow a truck for the trip. Of course, I have been working 10 hr days, 6 days a week since so progress on the other side had been slow. Finally got it all the way down today.

For those not familiar, the lb7 has 2 intake and 2 exhaust valves, but only one rocker arm for intake and one for the exhaust. They accomplished this by using a bridge plate over the stems of the two exhaust valves and the rocker arm pushes on the middle of the bridge plate.

So it seems that I did not have the bridge plate on the exhaust valves fully seated on the rear most cylinder on the driver's side. And now, a year later, it finally caused an issue. When I got it disassembled, I found the bridge plate pushing on the spring plate, not the valve stem on the lower most exhaust valve. This one is the one closest to the return line. The spring was being pushed on funny, apparently enough to Bush over and break the return line. That's where the leak was from.

Issue now is that one of the valve keepers is missing. Using the glow plug hole for access, I used a fitting from a compression testing tool to put air to the cylinder. This keeps the valve in place while removing the spring. Valve appears to be fine, moves easily, not bent. Got very lucky.

Unfortunately, the keepers that the parts store got me were the wrong size, so I was unable to reinstall today.

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I’ve been following along. Glad the glow plug air in the cylinder trick is working for you. A lot of work to replace that return line but thankfully a cheep fix for you.

Oh the memories I’ve had my sons lb7 apart 3 times. And it gets to come apart again. Plus my old Lb7 needs to come apart as well... if I don’t sell it the way it is?