Tested my AOS today, what does this mean?
06-02-2017, 12:50 AM
#31
Rennlist Member
Thread Starter
Thanks for posting that Tex. Clearly my readings are high indicating my AOS is failing. Strange that when the load of the A/C was removed from the engine (A/C off) my numbers actually went up, now down as you would expect. I can't explain that.
FWIW my car is a 2003 with 21K original miles. Age matters more than mileage at this point.
FWIW my car is a 2003 with 21K original miles. Age matters more than mileage at this point.
06-02-2017, 01:00 AM
#32
Racer
Join Date: Jul 2016
Posts: 379
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for posting that Tex. Clearly my readings are high indicating my AOS is failing. Strange that when the load of the A/C was removed from the engine (A/C off) my numbers actually went up, now down as you would expect. I can't explain that.
FWIW my car is a 2003 with 21K original miles. Age matters more than mileage at this point.
FWIW my car is a 2003 with 21K original miles. Age matters more than mileage at this point.
06-02-2017, 11:09 AM
#33
Rennlist Member
Thread Starter
The only explanation I could come up with in my mind is that there is a leak in the diaphragm and the increase in load w/ the A/C on pulls the leak closed, such as if it was at the edge of the diaphragm or something. That is 100% speculation...I can take it apart when I get it out to see.
06-02-2017, 12:10 PM
#34
Former Vendor
When the AOS gets tired, the diaphragm will often soften up. Extended periods of exposure to engine oils only changed annually, that become acid laden will create this over time. There's 3 ways that an AOS can fail, and 6 different forms of symptom that the engine can exhibit based on what part of the AOS failed.
I have seen some cars that had the bad AOS masked by a MAF that was dirty, or failing, and the negatives canceled each other out, and made for a perfectly running engine that did not smoke, yet ate engine oil like an intoxicated fish.
It took the Porsche world years to start using manometer readings to measure AOS health, and unlike BMW, Porsche has never released manometer values for these engines. Like everything else, we've had to do all of that ourselves.
I have seen some cars that had the bad AOS masked by a MAF that was dirty, or failing, and the negatives canceled each other out, and made for a perfectly running engine that did not smoke, yet ate engine oil like an intoxicated fish.
It took the Porsche world years to start using manometer readings to measure AOS health, and unlike BMW, Porsche has never released manometer values for these engines. Like everything else, we've had to do all of that ourselves.
06-02-2017, 12:18 PM
#35
Rennlist Member
"yet ate engine oil like an intoxicated fish."
That's a new euphemism to me ! I have to remember it for sure
That's a new euphemism to me ! I have to remember it for sure
06-02-2017, 12:26 PM
#36
Race Director
Engine RPM will dip slightly when the AC compressor turns on - or at least it does in my car - if the car is warm and nothing else is on. Even a slight variation in speed at low RPM significantly affects vacuum, including crankcase ventilation.
If you turn the AC on/off at 7K RPM, the vacuum differential would be negligible, especially if the AOS membrane is damaged but not destroyed...
If you turn the AC on/off at 7K RPM, the vacuum differential would be negligible, especially if the AOS membrane is damaged but not destroyed...
06-02-2017, 03:24 PM
#37
Rennlist Member
Thread Starter
When the AOS gets tired, the diaphragm will often soften up. Extended periods of exposure to engine oils only changed annually, that become acid laden will create this over time. There's 3 ways that an AOS can fail, and 6 different forms of symptom that the engine can exhibit based on what part of the AOS failed.
I have seen some cars that had the bad AOS masked by a MAF that was dirty, or failing, and the negatives canceled each other out, and made for a perfectly running engine that did not smoke, yet ate engine oil like an intoxicated fish.
I have seen some cars that had the bad AOS masked by a MAF that was dirty, or failing, and the negatives canceled each other out, and made for a perfectly running engine that did not smoke, yet ate engine oil like an intoxicated fish.
That would make sense given that my car is 12 years old with only 20K miles on it. I'm sure it sat a lot. The car is new to me and I don't have much history beyond the last 2 years. I do see suggestions that the car was tracked or autocrossed at some point, there are 5 point harness eyelets hidden under the carpet and I have found track rubber stuck under the wheel arch linings...so it could have been some hard miles in that 20K but given how nice the paint looks (and I believe it's all original paint) I doubt it saw more than occasional track use. Having owned a track-only car myself in the past I know how the track tears up the paint w/ rock chips.
The point is that the car probably sat around a lot, driven only occasionally over it's life. Most likely this was mostly street driving with a few trips to the track or autocross but probably not much. So not surprising to see the decay of what happens when cars sit around and are not driven.
06-03-2017, 10:15 AM
#38
All this AOS talk got me nervous so...Got car hot, turned off A/C, put on test oil cap, used same tester as the OP and got 5.2 to 5.35! I would be insanely happy if not for the ticking on the right side of engine!
06-03-2017, 11:48 AM
#39
Former Vendor