Leak down test in #1 if you have the injector adapter. Our use an old injector with the guts removed and the return lines blocked off and put in 15 lbs of pressure if the head gasket failed on an oil galley then air will come out the cap. Lots of Vw injectors also fit and maybe easier to source at the yards. A similar failure happened on my 602 last year but it was the a coolant leak at #5.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

$1500 later, valve guides & seals replaced & head resurfaced. Oil consumption has decreased to about a quart every 500 miles now but is still present. Smoke from exhaust is still observed on start-up but once car is warmed up, becomes pretty much non-visible & even on start-up seems to be getting less all the time. Mechanic explained that much of the 'consumed' oil is still in the CAT & mufflers but should eventually burn off. Exhaust fumes smells like tater-tots or a fish-fry (did I mention I've been running exclusively on B99 for last 10k?) The oil return tube from turbo was discovered to be leaking as well & that has been rectified w/ a new seal gasket. I had been using Rotella T6 0w30 synthetic & have since switched to using non-synthetic Rotella T 10w40 at recommendation of mechanic & also because it's cheaper. Oil pressure guage function had been intermittently dropping to 0 when synthetic was used & has now stabilized to between 2 & 3 @idle & pegs 3 @rpm's above 1500. Synthetic is too thin & not designed for 60x engines according to mechanic. Vehicle's odo read 268K @time of repair & is now @269K w/ no signs of imminent failure on horizon. Motor is a little noisier on idle than it was prior to repair & kinda reminds me of a 617 now more than a 602 but knocking sounds fade quickly into a synchronous symphony when accelerating. Mechanic is an optimist, predicting good for another 200K Since crisis, I've been looking @possibly trading up to an 05 or 06 e320 CDI but will continue driving my 92 300D until I can find an E320 CDI that has all the right stuff @the right price. All & all, I'd say valve job was probably a good call but time will tell. At least, 300D's reliability has been somewhat restored & thoughts of imminent doom & failure are fading. Thanks to all who have replied & your suggestions & advice are well received.

Much of the current oil consumption reduction may be just the switch to a heavier 15-40 oil. Now to me it is a toss up if the 0-30 oil was not protecting well enough that excess wear occurred on your long highway trip or the turbo seals are leaky.

The oil pressure at zero with the 0-30 either was not the best thing. Next oil change if the weather is still going to be decent for awhile. Put a straight 40 weight diesel oil in.

If oil consumption drops to about half of what you are experiencing now. I suspect serious engine wear occurred. Especially if the oil gauge was not pegged at the top on the highway at times during the highway trip at speed with the 0-30. Even if that was not occurring excess wear could have still happened.

At one quart for five hundred miles if what I am thinking may have occurred. Two hundred thousand more miles on that engine was far too optimistic. Once serious wear is present the ratio of the existing wear increasing accelerates.

If the car is in decent shape otherwise. Perhaps a good used engine could be located cheap over time and held for when needed. You can always resell it if never used.

Yes, that's what's such a bummer... interior is still real nice & car is still comfortable & pleasure to drive. No rips in seats & still blows icee-cold A/C on a 100F day but in 6 yrs. I've racked up a mountain of repair receipts so have pretty much decided to throw in the towel & look for something new before next failure which I believe is not far off. I've just discovered oil consumption is erratic now since valve job. I've driven as high as 400+miles @75mph by night w/ ambient temp around 80F & not burn a drop & then go on a 100 mile journey in stop & go traffic during daylight when temp is 95+F & burn a 1/2 gallon! I'm looking hard for an 05/06 E320 CDI now & have been road-trippin all over Florida to find one I like. Prices on those are really sliding lower nicely.

How long were you using synthetic oil for? Switching back to Dino has been known to cause some leaks in the seals after a period of time from what I had observed and been told by others.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

This is more obscure. A few Members have said when the litttle O-ring that seperates the Fuel Supply/Lift Pump from the Oil inside of the Fuel Injection Pump goes the Fuel Supply/Lift Pump sucks Oil into the Lift Pump and mixes the Oil with the Fuel and it is atomized by the Injectors and the Oil is burned as Fuel.

There is 2 threads on installing a Fuel Supply/Lift Pump kit to fix the issue.
In post #7 there is a cutaway drawing of the Fuel Supply/Lift Pump. #1 in the Drawing shows the little O-ring.
OM606 re-timing of injection pump: diesel fuel in engine oil

The other one has already been mentioned. The Turbo Seals.

If the Exhaust Turbo Seal is leaking if you remove the Pipe to the Exhaust the Carbon inside will look shiny. If the seal is good the Carbon will be dry.

If raw Oil is getting into the Combustion Chamber when you pull the Injector and heat shield it the Carbon in the Precombustion Chamber will also look shiny instead of a dry flat balck color.

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84 300D, 82 Volvo 244Gl Diesel

Injection pump, huh? I wonder if this could be the issue... I'd like to believe it's something other than piston rings because engine sounds & runs very smooth still. Motor has never gotten hot or over-revved. I thought running bio-diesel ultimately would be better for engine than ULS #2. It definitely smells better & makes engine run smoother & get better mileage. I buy it in Melbourne, Florida at business called Glover's Oil that retails B99 for $2.30/gallon & that's with road taxes already added into price. I go over there with 6 5gallon jerry cans & empty tank on car & fill up everything for just over $100 which lasts me approximately 2100 miles of driving. When I look at all repair receipts I've piled up on this car, I'm disgusted. Especially now that I'm seeing what these newer MBs are selling for. I could have a fleet of them by now for as much as I've sunk into this 300D. Oh & I've been using synthetic for about 50K miles. It's @ 269K currently.

Bummer for sure. I think I would take it back to the mechanic and see if they would do a leak down test and hopefully eliminate rings a a problem. That should be a free one as they maybe mis diagonised the cause of the oil consumption.

A random thought here but the lift pump O ring as diesel911 stated may well be the issue just wondering if this could be tested easily by placing a vacuum on the fuel supply to the lift pump with the other end of the fuel line blocked? Of course it isn't a big deal to just replace that O ring. I don't think you are too far away from identifying your issue.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

It is with heavy heart but after much deep thought & consideration, I've decided to trade this car in for something newer. I've invested a small fortune in it over last 5 years & put about 65K miles on it in that time but have decided it's time to cut my losses & move on. I've been offered $800 trade-in value on it to put towards an 05 E320 CDI. This is lower than I'd hoped for but considering what's going on with oil consumption & mileage of car, feel this is probably about as fair a deal as I'm going to get. I will miss this car, have had some good times in it but look forward to even better times in new to me E320 CDI!

Sad. In my opinion, all mechanical problems are fixable. The challenge is getting a right diagnosis. Any car is only as good as its mechanic. Ask me how I know: I have a '91 300D 2.5 with 330,000. Breakdowns -- and $$$ spent -- was mostly caused by faulty work. My suspicion: your current oil gremlin started with biodiesel. Good luck with your E320.

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'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate