When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Ok so now I am really confused. Tonight after work I tested again using my homemade manometer as well as retested with the digital manometer.
Both of them show about 5.5-5.8 inH2O now.
Why would I be getting different readings now? When I tested and got the 12.5 on the digital manometer I had driven the car about 45 minutes in about 65 degree ambient temperatures. Tonight when I tested I had drive the car home from work, about half city, half highway, in 80 degree ambient temperatures and got the 5.5-5.8 inH2O.
In your first picture, you're measuring the manometer wrong. The measurement should not be from the open end to the top of the fluid, but the difference from one side's fluid level to the other. Doesn't look like a huge difference, but still worth mentioning. Kinda hard to judge perspective in your picture, but it looks like the measurement is around 7.5" of oil, or 6.4" of water. I would trust this measurement over what was done with the digital one since we don't know how that's calibrated or how good that instrument is.
The magic number is 5 inches of water, up to 6 is normal... When I see more than 6.25 I get suspicious.. When its over 7 the AOS is weak for sure.
I do the test with the AC off, idle speed of less than 1K, and the engine fully warmed up.
In your first picture, you're measuring the manometer wrong. The measurement should not be from the open end to the top of the fluid, but the difference from one side's fluid level to the other. Doesn't look like a huge difference, but still worth mentioning. Kinda hard to judge perspective in your picture, but it looks like the measurement is around 7.5" of oil, or 6.4" of water. I would trust this measurement over what was done with the digital one since we don't know how that's calibrated or how good that instrument is.
Yes I was trying to hold it and take a photo at the same time. I was intending to hold the left end of the tube even with the oil level on the right when measuring. While watching it I noted it hovered between 6.5 and 7.5" of oil depending on how high I held the apparatus relative to the engine level. Regardless whether it's 6.5" or 7.5" it's still well within spec for the AOS.
What is perplexing is I was seeing a measurement of 12.5 on my digital meter, but now it shows similar to the slack tube at 5-6 inches measuring the same way as I did yesterday getting 12.5. Is the AOS function temperature dependent? The car was hot when I was getting 12.5, but it is hotter today than yesterday when I got the 12.5 readings. I took all these readings more than one time so I don't think they were any sort of error. Thoughts?
Yes I was trying to hold it and take a photo at the same time. I was intending to hold the left end of the tube even with the oil level on the right when measuring. While watching it I noted it hovered between 6.5 and 7.5" of oil depending on how high I held the apparatus relative to the engine level. Regardless whether it's 6.5" or 7.5" it's still well within spec for the AOS.
What is perplexing is I was seeing a measurement of 12.5 on my digital meter, but now it shows similar to the slack tube at 5-6 inches measuring the same way as I did yesterday getting 12.5. Is the AOS function temperature dependent? The car was hot when I was getting 12.5, but it is hotter today than yesterday when I got the 12.5 readings. I took all these readings more than one time so I don't think they were any sort of error. Thoughts?
Based on Jake Raby's response above and the fact that you are having readings over the threshold that he recommends as well as the higher reading earlier, I would think about replacing the AOS. If you have some mechanical skills, you should be able to do this yourself and save a ton. Although Pelican has a DIY article for replacing the AOS, I would search here on rennlist since I have found allot of additional helpful hints that the Pelican DIY article does not cover. Why take a chance on a $140.00 part that is known to go bad and in the worst case could cause catastrophic failure. Just my two cents.
Based on Jake Raby's response above and the fact that you are having readings over the threshold that he recommends as well as the higher reading earlier, I would think about replacing the AOS. If you have some mechanical skills, you should be able to do this yourself and save a ton. Although Pelican has a DIY article for replacing the AOS, I would search here on rennlist since I have found allot of additional helpful hints that the Pelican DIY article does not cover. Why take a chance on a $140.00 part that is known to go bad and in the worst case could cause catastrophic failure. Just my two cents.
After reading his post I am thinking the same thing. According to Pelican's tech article they feel that up to 7 is OK, maybe even up to 9. Clearly Jake is the authority on this so I'll have to go with his numbers.
I'll probably just drop the engine and transmission, it seems easier to do that than trying to change it with the engine in the car. I know my way around the garage and have done some engine, transmission, differential, etc building in the past and I have an EzCarLift in my garage which should make the drop relatively easy.
Thanks for everyone's help on this. I have various cooling system stuff to do this winter so I hope this AOS will last until then and I can tear everything apart at once.
Not to add to your confusion, but it looks like you have your home-made tubing filled with oil - good idea since it won't contaminate the engine. But, while the difference is minor, the density of water is 1000 kg/m3, and oil ca. 850. Your post #17 shows an instrument reading well within spec.. Without any symptoms (smoke, whale call noise, etc.) I'd be somewhat comfortable until you have reasons not to be.
So here is something interesting....I got to thinking about the two different testing results I got with the digital manometer. The first time I tested was with the A/C off and was getting readings of 10-12. Yesterday when I tested with both the digital and the homemade slack tube manometer I was getting similar readings of 6-7ish. So I realized that the first time I had the A/C off and yesterday I had it turned on.
So tonight after work I retested it with the digital manometer with the A/C off and On. Here's what I saw:
A/C on = 6.0-6.3 inH2O
A/C off = Vacuum steadily increasing from 6.0 up to about 10-12.5 after turning the A/C off.
Now why would turning the A/C off cause an increase in crankcase vacuum? Is there some component of the A/C that would affect crankcase vacuum?
No idea but in Jake's response he noted that he does his test with A/C off and rpm's under 1000. I can not remember if when I tested mine the A/C was on or off so I may play around with it tomorrow and see if I get those types of variations. Will keep you posted.
No idea but in Jake's response he noted that he does his test with A/C off and rpm's under 1000. I can not remember if when I tested mine the A/C was on or off so I may play around with it tomorrow and see if I get those types of variations. Will keep you posted.
Thanks that would be great. My car idles well below 1000 with both the AC off and on. I'll be interested to see what yours does.
The difference comes from engine load that increases with the AC engaged. AOS vacuum depends on intake manifold vacuum, as the AOS bridges the crankcase to the throttle body.
The higher the load, the more the deviation you'll see from the AOS reading.
Dont over think this. Leave the AC off and test the AOS. All the empirical data we have for AOS health via manometer has been gathered and compared with the AC off. Leave it off.
Yes the engine can run perfectly and have a weak AOS that fails the manometer test.
The difference comes from engine load that increases with the AC engaged. AOS vacuum depends on intake manifold vacuum, as the AOS bridges the crankcase to the throttle body.
The higher the load, the more the deviation you'll see from the AOS reading.
Dont over think this. Leave the AC off and test the AOS. All the empirical data we have for AOS health via manometer has been gathered and compared with the AC off. Leave it off.
Yes the engine can run perfectly and have a weak AOS that fails the manometer test.
Clearly based on that then my AOS is weak at the least as the readings w/ the A/C off are approaching 12.5 inH2O. Guess I'll keep the A/C on until I get a chance to replace it!
As Jake mentioned, we are over thinking this. Since his data is based on an up to temp engine at idle with air conditioning off, we should use his data as a bench mark. I do not know of anyone else that has evaluated the AOS in the detail that he has. With that said, the following if for curiosity only and should not be used as a reliable source in determining the condition of your AOS.
I performed some additional testing of the crank case pressure. I drove the car for approx 30 minutes on some back windy roads (wanted to have some fun) then performed the crankcase test with my Dryer Series 475 Mark II Digital Manometer. I have this Manometer calibrated annually as required in the standards I use it for.
The 1st photo shows the hook up of the manometer. The 2nd photo shows the reading of 4.55 inches of water with the air conditioner off and at idle. The 3rd photo shows the reading of 4.81 inches of water with the air conditioning on. There was a slight rise in pressure and I could hear the additional load on motor when turning on the Air.
Again, not sure this means anything but the OP had the same curiosity as I did although his readings were greatly different. Some additional info, my car has approx 60,500 miles on it and I had the 60K service performed approx 1,000 miles ago.
05-30-2017, 09:45 PM
