Black oil at low mileage
10-07-2005, 10:55 AM
#1
Rennlist Member
Thread Starter
Black oil at low mileage
Any causes of blackened oil, other than ring blow-by?
The oil in my 87T comes out almost pitch black in under 500 miles. I assumed it was from a tired engine with low compression and bad ring leakdown. So I just replaced the engine with a rebuilt one, and the oil still comes out black. The first oil change after 500 miles of low rpm break-in was black. This has been the case using both Mobil 1 and Amsoil.
I dont see any evidence of an over heating problem. The oil doesnt smell burned, it smells like combustion gas. Which would be rings. I have not checked the leakdown on the new/rebuilt engine - so maybe some of the rings did not seat, but that would be unusual. It was a low mileage block and the bores looked very good.
Cant think of how the turbocharger could be causing it - although it does blow a significant amount of oil into the intake (more than the other two 944Ts that Ive had).
For comparison, my other and previous 944s do not do this using the same oils and even with significantly higher miles and track use. Sure the oil will darken with mileage, but nothing like with the 87T.
Thanks for ideas/comments.
The oil in my 87T comes out almost pitch black in under 500 miles. I assumed it was from a tired engine with low compression and bad ring leakdown. So I just replaced the engine with a rebuilt one, and the oil still comes out black. The first oil change after 500 miles of low rpm break-in was black. This has been the case using both Mobil 1 and Amsoil.
I dont see any evidence of an over heating problem. The oil doesnt smell burned, it smells like combustion gas. Which would be rings. I have not checked the leakdown on the new/rebuilt engine - so maybe some of the rings did not seat, but that would be unusual. It was a low mileage block and the bores looked very good.
Cant think of how the turbocharger could be causing it - although it does blow a significant amount of oil into the intake (more than the other two 944Ts that Ive had).
For comparison, my other and previous 944s do not do this using the same oils and even with significantly higher miles and track use. Sure the oil will darken with mileage, but nothing like with the 87T.
Thanks for ideas/comments.
10-07-2005, 11:47 AM
#2
Race Director
Hey, I have that same problem with my 150K + N/A. Don't know anything about it, as I haven't researched it yet (too busy dealing with the million other things wrong) Have you taken a compression test? It should tell if your rings are messed up, right? I think I'll take one now.
BTW, nice cars
Mike
BTW, nice cars
Mike
10-07-2005, 12:06 PM
#3
Mexican Ambassador
Lifetime Rennlist
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Lifetime Rennlist
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i have almost the same problem, but i'm getting some consumption too. usually only when on boost. the thing is, i had a compression test done, and it was 145-150 across all 4, and the plugs had a bit of oil on them, 
. btw- what is normal compression for 951's?
. btw- what is normal compression for 951's?
10-07-2005, 03:09 PM
#4
Race Car
Well, it was rebuilt, correct?
Was it bored out, were the cylinders within spec, etc?
Also, did you just say you used a synthetic oil for the first 500 miles?
During the break-in, a freshly rebuilt engine will darken the oil quicker than a normally running one.
My engine also does the same thing, but then again, I had upside-down rings on one cylinder, I suspect that was my cause, but my problem was also coupled with excessive oil consumption, so I doubt it's the same as your problem.
Was it bored out, were the cylinders within spec, etc?
Also, did you just say you used a synthetic oil for the first 500 miles?
During the break-in, a freshly rebuilt engine will darken the oil quicker than a normally running one.
My engine also does the same thing, but then again, I had upside-down rings on one cylinder, I suspect that was my cause, but my problem was also coupled with excessive oil consumption, so I doubt it's the same as your problem.
10-07-2005, 03:23 PM
#5
Rennlist Member
Thread Starter
Old engine in the car did it, then installed a rebuilt engine and it still does it. Rebuilt engine was not bored out, it only had 50k on it and the bores were in excellent condition, measured fine and the ring gaps with new standard rings were fine. To clarify, break-in (two oil changes in 800 miles) was done with regular oil, came out black; have gone to synthetic and it turns black in short order. Block was completely stripped and cleaned, so no residual dirt/carbon/residue inside the block that would discolor the fresh oil.
My 944S had its engine rebuilt about 8000 miles ago. Its a dedicated track car, and when I change the oil on it before events, it looks clean enough to drink - even the initial break-in oil changes.
Again, the only thing I can think of that would cause the black oil is compression blow-by past the rings. Before I start trouble shooting the old and newly rebuilt engines, Im just asking if there is some other potential source/cause of blackened oil?
My 944S had its engine rebuilt about 8000 miles ago. Its a dedicated track car, and when I change the oil on it before events, it looks clean enough to drink - even the initial break-in oil changes.
Again, the only thing I can think of that would cause the black oil is compression blow-by past the rings. Before I start trouble shooting the old and newly rebuilt engines, Im just asking if there is some other potential source/cause of blackened oil?
