Black Runny Oil

[SilverFive90]

90 E34 M20
Hi All,
I recently had my engine replaced - almost made it to 325k, and forgot about the freaking timing belt - Kaboom! Anywhoo, I recently topped off the oil (light indicated), took a very long trip. But when I went to work yesterday, I noticed that as I came to a stop the Oil Pressure sensor on the dash would light up. As soon as I applied gas, it'd shut off. A day later - I got the Check Engine light, but as soon as I put gas in and go, it'd go off. I checked the oil and it's runny and black. I'm taking it for a change, but should I be concerned that this could be a problem. Yes, I checked the oil when the engine was cold.

Thanks for any help and/or tips

[Ferret]

If it's really runny, like water, you may have coolant getting into the crank case?

Is there any brown stuff floating on the oil/mayo under the filler cap?

[whiskychaser]

Could be just the oil pressure sensor but if it was my car I wouldnt drive it until I'd checked the oil pressure with a gauge: you can probably get enough pressure up to knock that light out by turning the engine over by hand

[SilverFive90]

If it's really runny, like water, you may have coolant getting into the crank case?

Is there any brown stuff floating on the oil/mayo under the filler cap?

No brown stuff/floating or white....just black and runny. Coolant could be the issue, as it seems to happen if the car is really hot running the heat. Hmmm!

[SilverFive90]

Could be just the oil pressure sensor but if it was my car I wouldnt drive it until I'd checked the oil pressure with a gauge: you can probably get enough pressure up to knock that light out by turning the engine over by hand

I'm not too familiar with the oil pressure sensor, but I can look it up and have the mechanic change or if its a cheap fix attempt it myself. There aren't any leaks, the light apppears only when I'm in traffic at a standstill - intermittedly.

[SilverFive90]

How would the coolant leak into the crankcase???

[whiskychaser]

How would the coolant leak into the crankcase???

Item 15 here will be your oil pressure switch/sensor:
http://www.realoem.com/bmw/showparts...26&hg=11&fg=30
If the engine gets too hot the head gasket blows and/or the head warps. The seals on the seperate little bores coming up through the block and head (which carry water and oil) are then broken allowing water and oil to mix. This can also happen if the timing chain cover to head seal is broken.

[Grantus]

I have had those symptoms on cars other than BMW when the engine is well worn (including the oilpump) and the oilfilter is ready for changing.

[BMWCCA1]

How's your fuel economy? It could also be diluted with gasoline, if it's really runny and not just normal for hot oil.

I'd start by changing the oil and filter using the correct grade and weight as shown in your manual.

I don't trust an M20 any farther than I can throw one.

[Ross]

How's your fuel economy? It could also be diluted with gasoline, if it's really runny and not just normal for hot oil.

I'd start by changing the oil and filter using the correct grade and weight as shown in your manual.

I don't trust an M20 any farther than I can throw one.

Agree with all but the M20 trust issue, 325k should prove that.
Black is the last color oil will be if coolant diluted. Fuel dilution or just plain old broken down oil, in either case it needs to chnged immediately and monitored.