Joined: Sat Aug 24, 2013 11:36 pm
Posts: 7171
Location: Central GA
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Some real numbers to digest Ranger1 sent to me and OK'ed to share:  I retested crankcase pressure today with fully warmed up engine after a 30 mile drive, engine coolant at 178*F. I dug up some more industry recommendations on crankcase pressure on diesel engines for comparison.
Configuration - Provent 200 connected in series with OE CCV and turbo inlet hose, closed loop condition, closed drain pipe. Clean Provent filter. Compound gauge inserted tightly into dipstick tube vent. Slight blow by gases visible if oil cap removed. Engine at ~ 80K miles, in excellent condition, no oil leaks, runs like new. Rocketchip RC1 tune, Mobil 1 TDT 5W-40 synthetic oil, Amsoil ovesized EaO26 15 micron oil filter. Oil pressure at hot idle, 20 psi, oil pressure at 45 to 55 psi on acceleration, 44 psi at 50 mph steady cruise speed on fully warmed up engine. Performed all tests after a 30 mile run of stop and go errands of about 2 hours duration, with ambient temperature at 60*F and coolant temps at 178*F at the start of test. Oil and filter are at 600 miles of use.
Test 1: Provent 200 CCV Test
Engine at idle, crankcase pressure close to -0.1 psi. My gauge has 1/10 increments at the low end of the scale and it was just slightly higher than -0.1 psi. Starting the engine shows the gauge pointer dropping from 0 psi at engine off to -0.1 psi at idle. Revving the engine shows the gauge rising slightly but not reaching 0 psi and then decreasing psi with increasing rpm.
Engine at 1000 rpm to 3500 rpm, crankcase pressure drops smoothly from -0.1 psi to -0.15 psi, and stops, stays rock solid. Could not get it to go lower than -0.15 psi no matter how hard I goosed the accelerator. The OE CCV and the Provent 200 connected in series appear to be working well to limit turbo vacuum and prevent any pressure at all in the crankcase.
Test 2: EHM Test
I also tested the equivalent of an EHM configuration by removing the cap from the Provent. This effectively connects the OE CCV hose to atmosphere. The turbo inlet hose was still connected to the bottom outlet of the Provent. This removes the Provent and its coalescing filter from the closed loop completely.
At idle, close to +0.1 psi. Not on the negative side of 0 psi at all. Gauge needle was fluctuating a tiny bit at idle, which did not happen in closed loop. This was a no load test, just sitting in the driveway. The gauge needle smoothed out with increasing rpm, climbing smoothly in positive pressure.
Engine at 1000 rpm to 3500 rpm, crankcase pressure increases smoothly to positive pressure, from +0.2 to +0.3 psi at 2000 - 3500 rpm. While that doesn't sound like a lot of pressure, it exceeds Racor, Mann-Hummel, MBE and Caterpillar recommendations for crankcase pressure limits.
Test 3: OE CCV only Test
Removing the Provent from the CCV loop, by eliminating the coalescing filter, produced vacuum levels of -0.1 psi at idle, and ranging from there down to -0.3 psi at 3000 rpm. At no time did the crankcase pressure ever rise to a positive level. Based on Racor's design guidelines, this is excessive vacuum. If so, it could be accounted for by the OE CCV spring weakening over time and not regulating pressure flow as effectively as when new. Without knowing the design specifications on the OE oil separator, it's difficult to determine how it's holding up. Since I run the Provent full time, it's not an concern for me, but I note it here in case someone tests their CRD for comparison. The additonal .15 psi pressure drop of the Provent at 3000 rpm is within the Provent 200 graph specification and within the safe guidelines by Racor as well.
Thoughts on the pressure readings - using a $35 analog compound pressure/vacuum gauge isn't going to be extremely accurate, but it should be close. A digital vacuum/pressure gauge would be more optimal, but it wasn't available for the test.
Comparative Notes: I checked some common crankcase pressure limits (MBE-900 Service Manual, CAT PDF LEBW4958-02). In an MBE900 diesel engine, any crankcase pressure above .2 psi is considered problematic and diagnostic steps are listed to identify and remove the crankcase breathing blockage - if no blockage is found it is recommended to check the turbocharger for excessive air leakage into the crankcase via the oil return tube due to worn turbo seals. I tested higher pressure than .2 psi with my unloaded EHM crankcase pressure test.
Caterpillar, on their engines equipped with CCV closed loop systems recommends no more than +0.04 psi of crankcase pressure(1 inch of H20) relative to barometric pressure, or they state that oil seal leaks will occur. They also state that excessive vacuum will generate oil seal leaks. They recommend cleaning or replacing the CCV filter at every oil change. They also recommend not returning the captured oil/water mixture to the engine crankcase for contamination reasons, due to the large amounts of water vapor present in recovered crankcase fumes. They specify measuring crankcase pressure at the oil dipstick location when performing these tests.
This certainly seems to validate Racor and Mann-Hummels CCV crankcase regulated negative pressure designs. If oil seals in these diesel engines can withstand higher pressure than 1 to 2 psi, why are these manufacturer so specific on these very low crankcase pressure limits?
Based on Racor, Mann-Hummel, MBE and Caterpillar recommendations, I'd say that pressurizing our R428 crankcase via an EHM or any other mechanism is asking for oil seal problems somewhere down the line.
Observations:
Based on these no load tests, running with an EHM appears to be running with slight positive crankcase pressure on my CRD, no more than .3 psi at 2000-3500 rpm under no load conditions, but above the safe limit recommendations I found with 2 large CCV and 2 large diesel engine manufacturers. All of these tests were done in the driveway, with no load, representing the lowest blow by, engine crankcase pressure loading conditions. I suspect with WOT or towing, the blow by and crankcase pressure will be higher in open loop, always in the positive pressure region. This positive crankcase pressure does not happen on my CRD with the CCV operating in closed loop configuration.
Blow by gas levels.
Based on some Caterpillar specific referenced documentation I found on calculating engine blow by gases, the formula used is blow by gas in cubic feet per minute = hp divided by 120 on new engines, on worn engines divide by 40 (or 3X as much blow by gas in worn engines). With our engines running at 200 hp, we should see between 1.67 and 5 cubic feet per minute of blow by gas over its lifetime using these formulas.
Another study by Haldex-Leval shows around 6 to 18 liters per minute, per cylinder for 200 hp engines. That works out to 72 liters per minute or 2.5 cfm for our 4 cylinder engine at the high end of the scale. A safe estimate is 3 cfm on our engine in good condition, increasing to 5 cfm as it ages past 250K miles.
These studies claim about 60% of the blow by gas is generated by the pistons/rings and the remaining 40% largely from gases passing the turbocharger seals and pressurizing the crankcase via the turbo oil drain line, with a small amount coming past the valve stem seals.
Other observations from the Haldex/Lavel study show that blow by gas is influenced by torque load and temperature more than engine rpm and that sub-micron oil particle size droplet (.29 microns) concentrations increase greatly in the high torque load, steady state region of engine loading. Also, blow by gases, as we observed on our CRD's, is much higher on a hot engine/oil than when cold, by a factor of 3X to 4X. That study referenced future use of flow sensors to build an active oil air separator that could adjust its efficiency based on oil density and gas flow.
Based on these studies, it seems to me that our factory oil separator, with it's simple spring loaded rubber flap is little more than a gas flow regulator to prevent both excessive pressure and vacuum from building within the crankcase. It appears to have absolutely no capability of separating sub-micron size oil particles or even micron sized oil aerosol mist. It's only going to trap very large oil droplets at low gas flow rates - it's not going to provide much oil separation for highway driving and it will be especially ineffective at oil separation when towing or high torque loads. If the heavy oil mist entering the turbocharger and air intake of the engine is to be reduced, it will have to be by a coalescing or equivalent efficiency CCV filter added using an after market design. The OE CCV is a much better gas flow regulator than it is an oil separator.
Thoughts on diesel engine crankcase pressure
Based on the information from Mann-Hummel,Racor, MBE and Caterpillar regarding diesel engine CCV design, there isn't any doubt that they design for slightly negative regulated crankcase pressure, avoiding positive crankcase pressure by design. I was able to find a number of guides on DieselNet and elsewhere where positive crankcase pressure is described as an explosion danger in a marine environment in large diesel engines and is closely monitored and designed to avoid it completely.
While I don't think positive crankcase pressure is an explosion danger on our size engines, there is no doubt in my mind that they're running a regulated, slight negative crankcase pressure right from the factory and it's to avoid seal leakage problems down the road. It appears to me that the days of venting to atmosphere or inserting an unregulated air flow oil catch can in the CCV loop without consequences are long gone.Ranger1 _________________ Supporting Vendor and Moderator of LOST05 Jeep Liberty CRD Limited 
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I had to soak and wash it out with a bunch of chemicals to get it clean. I also did the EHM at the same time to keep the oil mist out of the cooler. 
