PCV System/Crankcase Pressure
01-04-2011, 03:19 PM
#1
PCV System/Crankcase Pressure
I have an ATQ V6 engine with 188K miles and manual transmission. For several months I’ve been noticing a slight burned oil smell, particularly after running the car and then stopping it. Recently the smell has gotten worse so I decided to dig into it. I see some oil leaking from the valve covers (that’s new) and there’s been oil leaking down the front and rear of the engine but I haven’t taken the time to diagnose exactly where it’s coming from. With these symptoms many posters say to check the PVC system first.
The long PCV breather hose that bridges both cam covers was replaced fairly recently (it shattered while I was replacing the coolant temp sender) and is fine. I cleaned out the short PCV breather hose in the back of the engine—there was “whipped butter” (oil mist and water vapor emulsion) inside but it was not clogged. To my surprise, the suction jet pump (the original one!) was not plugged and worked fine. The green check valve near the SJP, however, was plugged tighter than a frog’s butt. A few cleanings/soakings with throttle body cleaner freed up the diaphragm and the valve now works fine.
So I put everything back together and the car runs fine, as it did before. I still smell some oil but it’s only been two days and limited driving since I cleaned out the PCV system so I expect it will take several more days to tell for sure. I decided to test the crankcase pressure just for chuckles. I hooked up a low pressure gauge to the dipstick tube. The gauge maxes out at 25 OUNCES/square inch. I rigged up some plastic tubing so I could watch the gauge from inside the car as I drive. Except for a very brief little bump at start up, I get absolutely no pressure at idle or highway speed. I connected a less sensitive vacuum gauge and see a slight vacuum at both idle and highway speed.
What pressure should I expect to see? What does it mean that I’m seeing a very slight vacuum? Unfortunately, I didn’t make this measurement before I cleaned out the PCV system so I can’t compare.
The long PCV breather hose that bridges both cam covers was replaced fairly recently (it shattered while I was replacing the coolant temp sender) and is fine. I cleaned out the short PCV breather hose in the back of the engine—there was “whipped butter” (oil mist and water vapor emulsion) inside but it was not clogged. To my surprise, the suction jet pump (the original one!) was not plugged and worked fine. The green check valve near the SJP, however, was plugged tighter than a frog’s butt. A few cleanings/soakings with throttle body cleaner freed up the diaphragm and the valve now works fine.
So I put everything back together and the car runs fine, as it did before. I still smell some oil but it’s only been two days and limited driving since I cleaned out the PCV system so I expect it will take several more days to tell for sure. I decided to test the crankcase pressure just for chuckles. I hooked up a low pressure gauge to the dipstick tube. The gauge maxes out at 25 OUNCES/square inch. I rigged up some plastic tubing so I could watch the gauge from inside the car as I drive. Except for a very brief little bump at start up, I get absolutely no pressure at idle or highway speed. I connected a less sensitive vacuum gauge and see a slight vacuum at both idle and highway speed.
What pressure should I expect to see? What does it mean that I’m seeing a very slight vacuum? Unfortunately, I didn’t make this measurement before I cleaned out the PCV system so I can’t compare.
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