2002 LB7 Oil Buring Puzzle

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I diesel mechanic recently called, and reported a problem he was having with a customer's truck regarding a sudden appearance of oil consumption following head & gaskets replacement for a cooling system overpressure problem. Let me know if anyone can offer any advice. Thanks,



2002 LB7 Duramax cylinder head gasket replacement for coolant pressure now has oil burning in cylinders.

The truck originally arrived at our shop for excessive cooling system pressure. We replaced the head gaskets and head bolts, and installed replacement cylinder heads that a local machine shop does for us.

I understand that the GM service information indicates that we should not resurface the aluminum cylinder heads, but our machine shop does and have resurfaced Duramax cylinder heads multiple times with no problem.

Our concern now is after reassembling the engine, cooling system pressure is normal at about 3 psi, where before had 20 psi, but that the engine is now burning oil at idle. We performed a blow-by in inches of water column per GM 3100 rpm with 16 in max. We only had 3 in.

Did not perform compression test on cylinders but blow-by is within GM spec.

Pulled head back off having machine shop rechecking seals and guides around valves which they are saying are ok.

Machine shop is saying that the oil rings have to be the problem although this was not the original problem and the cylinder walls look good. The machine shop thinks that the engine got hot and the oil ring only may have been affected. I find that odd how this problem would appear after replacing cylinder heads and gaskets.

The only thing that would look like any relation is that machine shop did say that the valves on the heads removed from the engine looked like they ingested some dirt (valves) having 1/8inch gap rather .060”. The engine does have a open cone K& N air filter which I could see could be the reason or the dirt yet the cylinder walls look fine .The truck does have a PPE tune on it set between 80-120 hp and I don't know if he is towing much. It appears a previous owner installed a pyrometer, as the thermocouple is still there.

Has any one had any similar experience or any thoughts?

We did have an early 1999 7.3 PSD that we did a head job on that had ingested some dirt ( The early 1999 air box) that after installing rebuilt heads started pushing severe blow-by but not so here.

Matthew

[Kennedy]

I would first ask him to define "engine is now burning oil at idle"

Sounds more like a misdiagnosis for an injector issue likely created when teh rusty crap from the line exterior got into the bowl of the injector.

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I would first ask him to define "engine is now burning oil at idle"

Sounds more like a misdiagnosis for an injector issue likely created when teh rusty crap from the line exterior got into the bowl of the injector.

He said he knows the difference between the smell of motor oil and diesel fuel in the exhaust. He's convinced it's motor oil.

Jim

[DmaxMaverick]

Curious, to be sure. If it's a federal smog truck, it's anyone's guess. Turbo, perhaps.

If it's a CA smog truck, it could be a number of things, if it is in fact engine oil that's burning. Turbo, air filter (if restrictive, can cause crankcase vapor to be sucked into the intake), fuel in the crankcase (pushing oil/fuel into the intake via the PCV). A federal smog truck will just make a huge mess underneath.

Probably not the oil rings. If they were suspect, there should have been significant evidence of oil coking on the cylinder walls, piston crown gap, crown and bowl, as well as measurable blow-by. I suspect perhaps assembly lubes or a significant amount of oil may have been introduced into the cylinders and/or exhaust during the R/R that hasn't burned off. A good, hard run (loaded) should clear it up. Unless there's a significant oil loss from the crankcase, it will probably clear up over time. Oil accumulated in the exhaust system can take a long time to burn off. If it's a CA truck, this can foul the converter, and lead to its failure. Also, disconnect the CAC hoses at the intercooler and see what drains out. If there's significant oil there, it's being introduced into the intake, and not necessarily through the engine internals. If so, suspect the PCV (if it has one) or the turbo.

If it's just an "odor" of oil, it could also be only the oil brand of choice. Some brands (Rotella, specifically), will vapor off more of the additives for several hundred miles, which has a rather strong oil odor, compared to other brands.

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We did talk about the turbocharger being a possiblity, but he indicated the CAC piping was pretty dry and clean.... Plus, just idling, not a lot of flow is traveling through the CAC.

He mentioned that he has already removed the exhaust manifolds, so I asked if he could trace the oil to a particular cylinder. He couldn't - said it appeared pretty uniformly distributed.

The replacement heads are my guess... a crack perhaps, I dunno.

[DmaxMaverick]

Manifolds (plural)? That doesn't leave much. The only things common to both banks (outside the fuel system) is the intake, turbo, and crankcase. What are the chances of getting 2 bad heads, after being rechecked by the machine shop? No blowby (or other evidence), but rings on both banks suspect? Doubtful. Either the condition existed before the job, or something was overlooked during assembly. Perhaps the gaskets were installed improperly???

[Kennedy]

He said he knows the difference between the smell of motor oil and diesel fuel in the exhaust. He's convinced it's motor oil.

Jim

My response would be run 5,000 miles and log oil consumption...

[Mark Rinker]

Agree with JK - do a 5K, 10K mile test of oil consumption.

If current oil used is Rotella, switch brands after first 5K test...you'll see consumption slow or even stop altogether. Highly recommend Mobile Delvac.

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Manifolds (plural)? That doesn't leave much. The only things common to both banks (outside the fuel system) is the intake, turbo, and crankcase. What are the chances of getting 2 bad heads, after being rechecked by the machine shop? No blowby (or other evidence), but rings on both banks suspect? Doubtful. Either the condition existed before the job, or something was overlooked during assembly. Perhaps the gaskets were installed improperly???

I know.... he didn't call me till the disassembly had already occurred. I suspect he was getting a little blowback from his head guy about the problem not being his cylinder heads. I would have encouraged him to run the truck for 10-20 miles then see what develops before a teardown. If a teardown was called for, look carefully as each part comes off, looking for the source of the oil.

I agree that a synthetic oil reduces typical oil consumption by anywhere between 25-50% over a good petroleum oil.

Jim

[Mark Rinker]

I have done 10K oil change intervals for all Duramaxes owned, (after break-in for the one purchased new.)

In a pinch (usually on the road) have allowed Rotella to be substituted. In each case, and most recently with Rotella Synthetic (http://www.shellusserver.com/products/pdf/RotellaTSynthetic.pdf)- I will lose at least 1-2qts in the next 10K interval, and in one extreme case - a shocking 3qts in a single 10K change interval, enough for the dash message of 'OIL LOW' to be illuminated! :eek:

Each time this has occured, I have switched back to Mobil Delvac - and oil consumption stops immediately - i.e. no quarts added in the very next 10K interval.

Rotella literally stinks - because its vaporizing out of your engine. Why do you think they sell it at Wally World?