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.do?model=HD68&mospid=47405&btnr=11_0526&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.

[BMWCCA1]

Agree with all but the M20 trust issue, 325k should prove that.I don't mind anyone defending their M20. My experience with them since they were new is far different. Just my opinion and not worth any more than anyone else's, for sure!

People used to try to impress me all the time with high-mileage claims on their MB diesels. Turns out the truth was they'd had many rebuilds or other major work to get there. I don't know of any M20 that can go much beyond 125k without a serious head-gasket leak. How long you put up with that depends on how much you like a clean garage floor, how much you mind adding oil, how long you can stand looking at that gunk all over your engine...or how many timing belts you replace before you forget that one time. In my experience an M30 will soldier-on without half the work an M20 needs and an M50 is almost as dependable as long as you don't overheat it.

[SilverFive90]

Item 15 here will be your oil pressure switch/sensor:
http://www.realoem.com/bmw/showparts.do?model=HD68&mospid=47405&btnr=11_0526&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.

I don't think it's the engine, the temp stays pretty straight in the middle and has worked perfectly indicating when somthing does go wrong (antifreeze, thermostat, etc.) Usually water makes it cloudy right? It's not milky, just straight black.

[SilverFive90]

I don't mind anyone defending their M20. My experienced with them since they were new is far different. Just my opinion and not worth any more than anyone else's, for sure!

People used to try to impress me all the time with high-mileage claims on their MB diesels. Turns out the truth was they'd had many rebuilds or other major work to get there. I don't know of any M20 that can go much beyond 125k without a serious head-gasket leak. How long you put up with that depends on how much you like a clean garage floor, how much you mind adding oil, how long you can stand looking at that gunk all over your engine...or how many timing belts you replace before you forget that one time. In my experience an M30 will soldier-on without half the work an M20 needs and an M50 is almost as dependable as long as you don't overheat it.

Haven't experience half the issues you're talking about, especially with the oil leak. Sure, I've put money into it, but it mostly was suspension and a drive shaft. The engine blowing was completely my fault for not staying on top of my service records. Your experience is yours and that's good, but you can't knock a car that drives 500+ miles weekly, can still cruise with the best of them and still turns heads. It's a keeper-as demonstrated by my trust to replace the engine. I think you had a bad run, but that's just a guess.
I have a 325i cabrio too, same engine, it's had work, up to 250k miles now. It's how much you care, not how much you spend when it's all said and done. Just my .02.

[SilverFive90]

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.

Thanks. Mileage by the way is surprisingly very good. I push 500 miles a week at least. Wash DC/Baltimore commuter. I will have it changed immediately.

[Rick L]

Just curious... How old is the replacement engine? Do you think you replaced with worn-out engine? If coolant in oil, you should see brownish / milky stuff. Check tip of the dipstick.


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.