Compression and Leakdown Tests
02-07-2003, 09:30 AM
#1
2nd Gear
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Compression and Leakdown Tests
Hi guys/Gals:
Have a 1983 911SC which seems to be leaking a little oil out of the tailpipes (I use sport exhausts), and coating the rear valence with a film of oil. The oil level is going down a little per 1000 miles, and there is a little seepage somewher high in the engine (can't see its origination looking up, and nothing visible from the engine compartment. The car still runs strong, no chugging sounds like leaking cylinder/case gaps, and there doesn't seem to be anything "wrong" with the engine except for this filming and tiny drips onto the exchangers.
Question: can the seals or the rings be causing the filming through the exhaust? Would a compression and leakdown test pinpoint such problems? Can somthing like this be "fixed" without pulling the engine?
Thanks for your help.......Andras
Have a 1983 911SC which seems to be leaking a little oil out of the tailpipes (I use sport exhausts), and coating the rear valence with a film of oil. The oil level is going down a little per 1000 miles, and there is a little seepage somewher high in the engine (can't see its origination looking up, and nothing visible from the engine compartment. The car still runs strong, no chugging sounds like leaking cylinder/case gaps, and there doesn't seem to be anything "wrong" with the engine except for this filming and tiny drips onto the exchangers.
Question: can the seals or the rings be causing the filming through the exhaust? Would a compression and leakdown test pinpoint such problems? Can somthing like this be "fixed" without pulling the engine?
Thanks for your help.......Andras
02-07-2003, 01:58 PM
#2
RL Technical Advisor
Hi Andras:
Oil leaks are not uncommon to high-mileage 911's and are normally no cause for concern unless they become severe or an annoyance.
If you are consuming oil at a rate of a qt in 600 miles or less, then either oil leaks or oil consumption are issues to be resolved with as soon as possible. For reasons of detonation-causing deposits inside the engine, its not good to ignore any engine that is consuming oil.
If you see an oil film on the back of the car, this can be either those leaks you spoke of or oil consumption from worn valve guides or rings. At this juncture, I'd suggest that you perform a compression test and followed by a leakdown test that will help pinpoint the cause of any lower-than-normal compression readings. Leakdown tests will tell you nothing about valve guide wear but it will surface any ring issues.
Lastly, certain kinds of oil leaks can be dealt with without major disassembly of the engine but if the compression & leakdown test results show any porblems, you will need to open it up to fix whatever is wrong or worn out. Oil leaks from "higher up" can be from the case through-bolts and the cylinders must be removed to deal with this effectively.
Oil leaks are not uncommon to high-mileage 911's and are normally no cause for concern unless they become severe or an annoyance.
If you are consuming oil at a rate of a qt in 600 miles or less, then either oil leaks or oil consumption are issues to be resolved with as soon as possible. For reasons of detonation-causing deposits inside the engine, its not good to ignore any engine that is consuming oil.
If you see an oil film on the back of the car, this can be either those leaks you spoke of or oil consumption from worn valve guides or rings. At this juncture, I'd suggest that you perform a compression test and followed by a leakdown test that will help pinpoint the cause of any lower-than-normal compression readings. Leakdown tests will tell you nothing about valve guide wear but it will surface any ring issues.
Lastly, certain kinds of oil leaks can be dealt with without major disassembly of the engine but if the compression & leakdown test results show any porblems, you will need to open it up to fix whatever is wrong or worn out. Oil leaks from "higher up" can be from the case through-bolts and the cylinders must be removed to deal with this effectively.
02-10-2003, 08:22 AM
#3
Are you sure the oil is leaking from the exhaust?.....most oil that drips onto the exhaust gets burnt off quickly unless there is a severe leak....assuming it's coming from elsewhere if it's spraying onto the rear valance and around the outside rear of the car then I would look under the motor first.....maybe where the engine connects to the transmission or the oil tubes...Steve is absolutely right when he says an older motor can leak oil but it shouldn't be blowing oil out of the back ..my 'informed best guess' is it's from the bottom of the engine rather than the top
