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

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

Thanks. I will check if there are new clips on the replacement sensor wire. I did this once before about 10 years ago, but I don't remember it. I just remember that it wasn't too difficult.

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