Oil disappearance diagnosis - PeachParts Mercedes-Benz Forum

rjk · #1 04-11-2004, 09:28 AM

Got a head scratcher I'm hoping someone has solved in the past. My daughter's '88 300TE is losing oil at the rate of approx 1 qt/100-200 miles. There is no apparent leak I can see either on top of or below the engine (I have put it up on a lift) and there is no evidence on the driveway (oil spots). Neither is there any evidence of oil in the coolant. I see no smoke (blue or otherwise) from the exhaust either idling or under power. The loss seems to come when the car is driven at highway speeds. The head looks as if it was replaced recently (I acquired the car last fall). What am I missing? Is there someplace the oil can be ejected at speed that would leave little or no trace under the car? Thanks in advance...

greenacres2 · #2 04-11-2004, 09:39 AM

Valve guide seals? Pull the spark plugs and look at the color--black would indicate burning. My 560 ran well with no noticable smoke but had the same consumption. Seals cut usage to less than a quart every 3,000 miles.

rjk · #3 04-11-2004, 09:43 AM

Were you able to replace the seals easily without removing the head or will I have to pull it off?

greenacres2 · #4 04-11-2004, 09:51 AM

Different engine, but i was able to do it with the head on mine. Rotated the engine by hand and worked each cylinder as it was at TDC using compressed air to hold the valves up. Don't know about the 3 litre engine.

#5 04-11-2004, 09:55 AM

That amount of oil burning is EXTREME and may not be solely due to oil seals. Black sooty spark plugs are not an indication of oil burning, they are an indication of rich mixture. I expect that your plugs will be very oily. I would also expect them to be fouled to a point that the engine is running very, very bad.

Before replacing the seals you should do a compression check. If compression is low, it will have to come apart anyway, so you can put new guides and seals in. If you just put in new seals without first checking compression, you could easily be wasting time and effort.

Good luck,

psfred · #6 04-11-2004, 12:23 PM

Replace the oil filler cap.

Peter

rjk · #7 04-11-2004, 12:27 PM

If the oil is being forced out around the oil filler cap, would it not show evidence by coating at least the valve cover?

psfred · #8 04-11-2004, 12:33 PM

Nope. Runs right down to the head, off the front and down off the engine. Only leaks at high speed when oil is thrown up from the camshaft.

Clues are no evidence of oil consumtion (no smoke, no fouled plugs, O2 sensor fine -- although yours is probably not if you are running rich), loss on the highway only. There will be a small amount of oil around the filler cap (there is a relief cast into the valve cover, so any significant amount drains off) and there will be a small amount on the drivers side only of the valve cover gasket. Oil will drain off the front cover just like a bad front cover seal, so there will be oil on the passenger side front. Runs off and into the sound encapsulation panel.

Looks all the world like slopping filling (and you are putting oil in once a week, right?).

If you drive a couple miles at low speeds after highway driving, all the oil drains off so you won't seen drips, and what is in the sound panel will blow out at highway speeds.

I had the same problem -- used 2 quarts in 500 miles once when I got the cap on crooked, then almost another quart on the way home. Replaced the cap and changed the oil, haven't used a quart yet in the 3000 or so miles Mom has put on it since.

Peter

rjk · #9 04-11-2004, 06:40 PM

Fair enough, I'll check it out. The cap seems to be nice & tight however.

greenacres2 · #10 04-11-2004, 07:08 PM

His approach is the proper one. I am new at this, and (with the help of reading this forum) have been able to guess right on some items. I've guessed wrong some too, and own some good used parts as a result.
Larry--is there any way to check the valve guides themselves before removing the seals? Or is that only going to be discovered in the midst of seal changing?
btw--the oil fill cap seal ring can be replaced for a buck or so, instead of the whole cap.

psfred · #11 04-12-2004, 10:36 PM

If you are actually burning a quart in 100 miles, you will leave a long, blue trail behind you, I've had cars that burned that much oil. You would also get blue smoke on startup and on deceleration bad enough to notice it, too.

Peter

TROVERMAN · #12 04-13-2004, 04:06 PM

I don't know...Our 1992 Range Rover for a while was using almost a quart every 500 miles, with absoutely zero smoke from the tailpipe. No check Engine light came on (although it did work) and the thing ran like a dream on the road. Always started, no fouled plugs, etc. The thing did stink when it ran like some old carburetted car, though. We used Lucas additive for "worn, high mileage, oil-consuming engines." That alone actually reduced consumption to a quart every 1200-1500 miles.

joe p · #13 04-13-2004, 08:04 PM

Dude, its a 103. Think about it.

The 92 wagon I had was burning a quart every 300 miles at 165K miles. I did a valve-job and viola!, no noticable useage in 5000 mile intervals.

The 88 wagon I had, same deal only worse, a quart every 150 miles or so. Valve-job fixed it.

Both of these mills now are deep into the 200's and other than some seepage from the oil pans are dry and happy.

Some people say do the stem seals but I see it as lipstick on a pig. Guides every 100K or so seem to keep the 103 in line.

None of the 103's I've had down for valve-jobs (I dont sell 103 headgaskets for oil leaks unlesss the customer wants to go there) had any noticeable wear in the bores. The only 103's I've seen with bottem end problems were beaten to death by either overheating or running them out of oil.

Joe