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Old 01-27-2017, 02:00 PM
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Join Date: Jan 2008
Location: NJ
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M103 engine burning lots of oil - valves or piston rings?

Hi All,

I have a 92' 300e (2.6L engine) with 148k miles and it is burning approximately 1 quart of oil every 500 - 600 miles. The previous owner used regular 5W - 30 oil and I am now using 20W - 50 to reduce the burning.

I changed the valve stem seals and the engine runs great but it burns excessive oil. The compression test was consistent across all cylinders (165) and the leak down test demonstrated consistent (10 - 12%) across the pistons. I do not see smoke coming out of the exhaust pipe. The spark plugs do have oil residue after a few thousand miles. I think it is also leaking a bit from the head gasket. The increased oil consumption also seemed to occur rather sudden.

Based on your experiences, do you believe it needs a head rebuild (valves, etc) or do you believe it is the piston rings? Is their a type of oil or additive I can add to reduce the oil consumption? Any other tests?

I truly appreciate any guidance since I don't want to spend the money to rebuild the head when the piston rings are bad. Thanks!

Best Regards,

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Old 01-27-2017, 02:13 PM
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148K seems a bit young to be bad piston rings. When you did the valve stem seals, did you also check to make sure the valve guides weren't worn out? If they're sloppy, they'll continue to leak oil, even with new seals.

Worth checking - is the oil leak external? Is it dripping down the outside of the engine or coming from a shaft seal?

Burning a quart every 500-600 miles I'd expect to see a blue haze in the exhaust and you'd CERTAINLY smell it!

If the car has been sitting a lot or only driven slowly/gently or in town, it could be gummed or varnished rings stuck in their grooves. A good high detergent oil and a hard romp on the highway for a couple hours should help if that's the case.
'91 560SEL - "Delta 88" 197K
'94 BMW 525i - "The Red Car" 181k
---Gone but not forgotten---
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Old 01-27-2017, 03:50 PM
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103 valve guides only last 150k miles.
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Old 01-27-2017, 04:04 PM
Hit Man X's Avatar
Join Date: Sep 2004
Posts: 9,087
Thumbs up

Did you make sure the stem seals are on the right guides? They are I/E specific when I did them years ago.

No way the bottom end is bad unless there was major neglect in the past. Compression test was done on my W126/M103 before and after the valve job around 275k, was all 160-170psi. Just as you received. Full of crosshatching in all six bores.

My M103 powered W126 rolled 315k last night and took a 3-4 WOT upshift like a pro to commemorate it. This car also turns 3400rpm @ 70mph, yours should be quite a bit less.

I would drop the coin on a top end if the car is decent. My total bill was around $600, most of that including $300 for machine shop labor to R&R guides, stem seals, skim of head with upper timing cover, and such. I replaced all 12 guides and all 12 springs while it was apart.
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

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Old 01-27-2017, 05:40 PM
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Location: NJ
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The mechanic had checked the guides while replacing the valve stem seals and he said they seemed good. I don't hear any valve tapping and the performance seems solid.

I added an additive to loosen and clean engine but it made no difference. There is oil leaking from the head gasket down the engine.

I do not have the tools or time to pull the head myself so I would have to pay to have it done so I am cautious about doing it. I am in NJ and I don't know who still does head rebuilds on these cars at a reasonable cost.
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Old 01-27-2017, 08:00 PM
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Join Date: Jan 2012
Posts: 7,515
Check the breather system for a clog. An external oil leak won't cause the spark plugs to oil up so pull the breather hose where it connects to the air intake system and see if you have oil there. I don't have a breather diagram to post for our guy, anyone have one?
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Old 01-28-2017, 10:57 AM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,181
Good compression... no smell... no smoke. M103s tend to consume more oil than most. After the dealer rebuilt my head on warranty at just under 50K including the latest valve seals, which were upgraded from what my '88 was built with it still used about a quart every 2000. These are high revving engines, and it seems they are setup a little on the "loose" side.

A buddy with a new '79 911 had to add a quart about every 600. Porsche said it was within the normal range.

Just check the oil at every fuel fillup and keep the level above the minimum on the dipstick, but don't overfill it. Wait until a real problem shows up before you start throwing money at it.

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Old 01-29-2017, 03:25 PM
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I've had opposite experience with my M103, the car has 207K miles on it but it doesn't burn or leak measurable amount of oil between 4K mile changes, has absolutely perfect compression. I don't know about valve stem seals or guides but all of the front end seals were redone recently.
Current: 80 300SD OM606 project, 83 300D 5-speed project, 88 Yugo GVX, 90 300D OM603 swap, 90 Lexus LS400, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L swap, 93 190E Sportline LE Megasquirt, 02 C320 wagon, 03 Sprinter, 06 E500 4Matic wagon.
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Old 01-29-2017, 04:26 PM
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These cars tend to leak more than they burn. Interesting phenomenon with this engines that it will leak from the front timing cover, migrate from the engine to the belly pan. It collects there until the next time you go on the freeway and it gets blown off. The result is no oil burning, and no spots on the driveway either!

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Old 01-30-2017, 10:54 AM
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Posts: 2,580
I had the valve stem seals replaced several years ago along with the seal at the front of the cam. That helped consumption for a while.

The M103 motor is an oil hog. They either leak it or consume it. For years I judged this motor the way I do all of my Asian cars. Big mistake. 20 yrs. later I've gotten use to how it works.

Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
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