For no apparent reason, after my engine comes up to operating temperature (usually after about 5 minutes), the oil quantity light illuminates. When I turn the engine off and restart it, the light appears immediately and does not extinguish for the remainder of the operating cycle.

When the engine has completely cooled down, I can start it up again and the light won't illuminate until it gets back to operating temperature.

The oil quantity is fine--right at the top plastic mark where it's always been.

Any thoughts?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

An aside MB suggests keeping the oil level midway between the min and the max marks. The problem sounds like either a bad oil level sensor or a bad lower engine wiring harness. The oil level sensor is inside the pan but taking the pan off is quite easy. If your lower harness is original and crumbling time to replace that too.

I agree that it's got to be either the sensor or the harness. I just can't figure out how either one relates to the temperature of the engine.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Conductivity is temperature related. I've had upper harnesses that were fine cold but would go bonkers when the engine warmed up.

I'll check the lower harness first. It probably needs to be replaced anyway. That would save me the cost of an oil pan gasket and sensor if it fixes the problem. Maybe I disturbed the lower harness when I changed the motor mounts a few weeks ago.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I confirmed that my lower harness is trashed. The insulation on the quantity and pressure sensors flakes right off, although the starter and alternator wires look okay (they are much larger). Does anyone know if this is a dealer-only item? I can't find it anywhere on line.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

http://www.peachparts.com/Wikka/W124StarterWireHarness

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

Fastlane has this for $105. Search for the PN in the DIY (1245403130).

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

That's a good price. Also not that hard to rebuild - starter and alternator wires are fine as suggested.

Thanks to both of you. It looks like the harness would have to come off in order to rebuild, so I'll just plan on replacing with a new one. The DIY post was something I had already printed out earlier. It's sharing experiences like this that makes this forum a great place.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

I followed Andras's DIY instructions and was able to replaced my lower harness in 2:45. His string idea probably saved me a few hours. I used an old telephone line and had a helper on top pulling it through the hole in the body toward the module box.

Unfortunately, my oil quantity light still comes on; so, now I know it's not the harness. In any case, I think it really needed to be replaced (pictures). The wires to the alternator and starter looked to be in better shape than the oil quantity and pressure wires.

You will need two 12" extensions and a 10 mm deep socket to get to the nut that holds the harness right where it goes up through the body. I think the hardest part of this job was trying to deal with the small nuts on the alternator, starter and the 10 mm harness mount nut. I also used a ratcheting angled screwdriver wrench from Sears to get to the small screw on the starter.

Please tell me I was right to replace this.

Attached Thumbnails

     

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Original so it had to be done eventually. Oil level sensor isn't that expensive or hard to do. E420 is one of the easier lower oil pans, maybe 20 allen bolts, no clearance issues, need a new pan gasket, a little extra torque when you put it back. I think it calls for 6 ft. lbs, better to do about 8. Inspect and clear your oil pump intake pipe screen while you're there.

Thanks. The sensor will be next. The dealer wants $61. There is no rhyme or reason why some of the dealer's parts cost less than you can buy them for on the secondary market and others are five times more expensive. I asked the parts guy if he thought the prices would go down if the Euro reached parity (or less), as I fully expect it will. He laughed and said they never go down--always up.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Things to consider when you have the pan off..

There is a rubber boot which holds the oil pump screen in place on the pump- the get old(ie fossilized brittle rubber). The sensor has 2 plastic clips to hold the wire in the routing with the engine. you'll need new clips if they don't come with a sensor.


M

FYI,

I did my 94' e420 harness a few weeks ago. I think it's faster and easier to leave the harness support @ bell housing in place and thread the new harness into it. It is mounted under the dipstick tube- so to get it out- you have the allen at the transmission, 17mm nut at the bellhousing with limited space, and the 10mm bolt at the back of the cylinder head on the passenger side.
Not a hard job at all..

Michael