1992 300D consuming a quart of oil every 60 miles
 

So I drove to Denver, CO from Orlando, FL 2 weeks ago & made the trip fueling with B99 biodiesel exclusively as it seemed to give better performance & mileage on a previous road trip of similar length. Car performed flawlessly & never got above 80C despite averaging 80mph w/ A/C on high entire time. I tried to drive mostly at night & averaged 1K miles/day. Prior to this recent trip, I had been filling up w/ ULS Diesel #2 & oil consumption was no more than a quart every 2.5K-5K. The vehicle is a little smokey w/ RPMs above 3K but runs evenly on all 5 & seems to have plenty of power. Minimal blow-by noted under valve cover w/ oil cap off. EGR is caked up w/ soot & oil but car leaves no drip puddles when parked. A leak-down test is in order to be sure with this level of consumption. Will it be bad piston rings or valve seals or other? How far is this motor from catastrophic failure? :confused: I've been carrying a bicycle on the trunklid like a dinghy just in case ever since I discovered this issue.

If it started happening all of a sudden my first thought is that something is going on with the crankcase vent system allowing oil to be sucked into the intake of the turbo.

It could still be a leak, you should drop the belly pan and see if it's filled with oil.

There is an oil/air separator built into the valve cover on 60x engines. It's workings are sort of a mystery, as the assembly is riveted together. It includes a pressure activated valve, a drainage chamber and a drain that allows oil back into the head. It's possible that either the valve is stuck, allowing blow by pressure to blow out a main seal, or it could be that the drain is clogged, allowing recovered oil to be sucked into the turbo. There's a tiny hole on the side of the valve cover that allows air pressure to equalize in the valve, if it's clogged the valve will stick. If you can't find any other possible cause, it may be worthwhile to remove the valve cover and clean this assembly out as best you can.

If it is not on the ground, or splattered all over the rear of the car, then it is going out the tail pipe.
Check for a leak from the turbo to the intake side.
Is the cross over pipe coated with black crankcase oil inside ?

The turbo berrings/seals could be dumping it also...

Suddenly down to 60 miles a quart. The head gasket may be breeched or leaking between the number one cylinder and the oil pressure passage to the head right in front of it. Pulling the number one injector and cranking the engine may spray oil out.

This is only one of a few possibilities of course. At the same time this type of head gasket failure is not uncommon on those engines either.

This problem can cause an engine run away situation, its very ugly when it happens.

This is a problem. Keeping the engine too cold will increase engine wear, and will also cause higher fuel consumption. You should be seeing engine temperatures of ~85 deg C. The thermostat is supposed to begin opening at 82 and be fully open by 90.

If you are confident that your temperature gauge is accurate, then I recommend you get a new thermostat which is correct for your car, and test it in a pan of water on the stove prior to installing. If you have doubts or want to double check, get a non-contact type thermometer (Hazard Fraught - err, Harbor Freight sells several inexpensive models, starting at around $25) and measure the temperature at the top front of the head (right at the aux. fan coolant temperature sensor/switch).

Thanks to everyone who replied. :) I've been talked into having the valve guides replaced. Fingers crossed this will rectify my situation. :undecided The tensioner pulley was also discovered on further inspection to be walking itself off it's mount bearing on front cover & closing in on the gap between it & the radiator fan. This will be sorted as well. I'll report back when repairs have been completed with update. Thanks again. :D

Typically, if valve stem guide seals are worn out you will see smoke on take off after sitting at a redlight or stop sign. Because of the amount of oil you are using I would suspect you have something going on that is causing the oil to be sucked into the combustion chamber.

{Perhaps worth adding?}

...and for valve stem seals you might notice plumes of smoke at start up because the oil has leaked into the cylinder when the engine is stopped

Figure out what is wrong first. I doubt valve guides unless one was broken during the trip. Almost an impossibility. Even then I doubt oil consumption would suddenly increase that much.

Certainly the valve guides may be worn. They wear over a long period of time and do not result in a sudden massive increase of oil consumption. Just a very gradual change over tens of thousands of miles at least.


Someone is giving you wrong expensive information in my opinion. You should prove what is wrong before doing anything else. It is almost always far cheaper to do so. There are many members on this site that are far more knowledgeable than myself. They can help you. Start with examining the cheap stuff.

It sounds like you may be on the verge of spending a lot of money that may make no practical difference. Unless when the head is removed the breech I suggested in the head gasket is observed. Then the need for additional work on the head is subject to need. If you are bound and bent on wasting money at least take a printoff of this to your mechanic first.

It is highly important when diagnosing that the oil consumption over a very short period of time and milage. Went from thousands of miles a quart to sixty miles a quart. Also tell your mechanic that this is a diesel and they are just not as subject to valve guide and seals type of issues. At least oil burning wise as gas engines of this manufacturer are.

There are three prime candidates for this problem. They are the turbo bearing seals, the head gasket and the engine breather system. Not the valve guides. Just trying to save you possibly needless expendatures. At the same time it is your money.

in a diesel you will not see the same blue smoke at startup from bad valve seals, the engine will use that oil as fuel and blow usual black diesel exhaust on starting.

It may sound like a can of marbles when starting up if the oil consumption is really bad.

I would also suggest to stop driving the car, if your engine decides to run away (the engine uses its own lubricating oil as fuel at uncontrolled rpm - imagine 12000 rpm or above) you could land in a dangerous situation whilst driving.

All very good ideas. Diagnosis while sitting still with the air cleaner removed and a metal cap for the turbo air intake is a good plan. If you really are sucking oil into the cumbustion chamber (a very real possibility) you stand a good chance of a runaway. The only way to stop one is to close off the source of combustion air - be carefull, the spinning turbo vanes will eat your fingers. Check the simple stuff first. Has anyone looked at the oil pressure sending unit? A leaky OPSU can still give a pressure reading while dumping oil. How about the fittings for the oil cooler? The oil filter housing? And so on. Just because the car doesn't leave a puddle, doesn't mean it isn't leaking. Good luck!

Valve stem seals are NOT your problem, if your engine went from consuming 1 qt per 2500 miles to 1 qt per 60 miles.

Let's think about this a little bit. Your engine is turbocharged. The turbocharger increases the air pressure in the combustion chamber above atmospheric pressure. Air will constantly be trying to escape from the combustion chamber, including going UP the valve stems. The only forces causing oil to flow DOWN the valve stems are gravity and wicking. Trust me, there is NO way that you can consume a qt of oil in 60 miles via the valve stems.

I think there are two other likely possibilities, already mentioned. The turbocharger, or a head gasket failure at the oil passage by the #1 cylinder. You need to pull the intake cross-over pipe to see if oil is flowing down that from the turbo, and also check the exhaust piping down-stream of the turbo. If there is no indication of oil in either place, then you need to find a way to test for the head gasket failure.