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The main issue with OEM crankcase vent is it is nothing more than a piece of hose mounted to the front of the gear case. The piece of hose elbows over the case and points down towards the ground. There are two versions of this crankcase. One involves a drip bottle mounted on the end of the hose and the other does not. A Technical Service Bulleting (TSB) was released on this issue as well: TSB (09-002-02 Crankcase Breather Overflow). This bulletin warns of potential of extreme loss of oil from a truck descending at to steep of a slope while off-roading. During this loss of oil, oil also has been known to scatter all over the engine and radiator. This scattering of oil causes the collection of dust and dirt in the face of the radiator. This collection causes overheating issues for your truck. Even in with normal use, the cases that include a breather bottle, can emit enough oil vapors make the radiator gunky with the collection dirt and dust. Another TSB on this issue is: TSB 09-02-00 (A Heavy Oil Or Fuel-Like Odor Coming From the Diesel Engine Compartment). This bulletin was written about the foul heavy oil smell after a oil change. Although it is normal for some brand of oils to have this heavy smell anyway. My own personal fix… To fix this issue, I personally created my own venting system for 2nd generation Cummins’ engines. Since my design I have never lost any oil while off-roading. When I first started creating my vent, I looked at one main simple principal. If the front of the truck is facing down hill, then the vent pipe end needs to be higher than the oil level at any angle. I did this by running the pipe up and over the top of the engine. Then I ran it back down the back side of the engine. So now, no matter how steep the hill, the end of the vent pipe will be higher. Since the end of the pipe is under the truck by the transmission, there are no problems with cooling or radiator plugging. The heavy oil smell is also gone since the pipe is now under the truck. I do not use rubber hose in my creation. Rubber heater hose will eventually break down and collapse. This will cause a build up of crankcase pressure and start oil leakage around seals, which is not a good thing! One other thing to be aware of if creating your own is the length of the vent. If the vent pipe is to long, it might start freezing the water vapor in the hose/pipe before it exits the pipe. This can once again cause problems with crankcase pressure Update April 25, 2009 - Vacuum Pump / Vacuum Lines It was brought to my attention from other members on forum sites that another cause for excessive oil blow by from the stock breather bottle is from the vacuum pump. If you happen to disconnect the vacuum line for servicing and forget to hook it back up the vacuum pump becomes a air compressor and pumping large amounts of air into the crankcase. This will make it appear that there is excessive blow by on the piston ring. So be sure to check your vacuum lines... Stock Crankcase Vent Mopar1973Man's Notes: Here is the result of leaving the stock crankcase vent in place and the problems it causes like overheating... Here is the story from Edcasey from Cummins forum at Should of lost my puke bottle a long ago