jaluhn83
Full Access Member
One of the common things I've seen is questions about what exactly the CDR valve is and what it does. Also, it seems pretty common for a "bad cdr" to be looked to for a cause of excessive oil consumption which makes little sense once you understand the working of the unit. My intent here is to shed a little light on the unit.
First of all, the question is what is a cdr valve? CDR stands for crankcase depression regulator. It's the can located on the back of the intake on a stock motor and mounted on the valve cover or the air box in turbo motors. Physically it's about 4" diameter and 1 1/2" thick with a 1" hole in the front face of the can going to the intake and a ~1" tube coming from the bottom of the can going to the valley pan. Functionally it's the link between the crankcase and the intake and serves to vent crankcase vapors (blowby with a small amount of vaporized oil) into the intake so that they're burned. This is similar in function to the PCV system on a gasser, but rather different in implementation due to the design of a diesel.
From my Ford 'Diesel Engine Operations' training manual:
"Some engines use a more complicated [than a simple tube from the crankcase to the intake] crankcase emissions system with a crankcase depression regulator. In this system, crankcase vapors must go through the crankcase depression regulator to get into the intake system. This device is designed to maintain pressure in the crankcase as close to atmospheric pressure as possible. A high vacuum in the crankcase will tend to draw dirt from the outside through the front and rear seals. This will result in shortened seal life. In addition, high crankcase pressure may cause lube oil to be forced out of the gaskets and seals resulting in leaks."
It is interesting that high vacuum sucking up oil causing a runaway is not mentioned as a reason for fitting the CDR system. Also note that minimizing oil consumption is not mentioned.
On a gasser the PCV system connects into the intake side of the throttle, so there is always going to be a vacuum on one side of the PCV valve. For the reasons mentioned above, it's strongly desirable to maintain nearly atmospheric pressure in the crankcase. The PCV valve thus acts as a regulator to block the crankcase off from the high intake vacuum, especially under closed throttle. Typical intake vacuum on a gasser is 15-20 inhg.
In contrast, the intake on a diesel is under a minimum of vacuum, at least as long as the inlet is free flowing. There is a slight vacuum, but it's minimal. From what I can find, this is typically ~5 in h20 (note the different units) with a healthy air filter. Of note, IH specifies a max of 25 in h20 air filter restriction. This is equal to ~0.9 psi or ~1.8 in hg. That is, the absolute max worst case plugged air filter operating condition is some 20 times less intake vacuum than a gasser. A more normal full throttle operating condition would be ~0.1 psi/0.2 in hg of vacuum. This is somewhat less than the vacuum you creating sucking soda up a straw at mcdonalds.
So now let's look at the inside of this puppy.....
Its very simple - exactly 2 parts within the can, a spring and a diaphragm. The port of the front of the can connecting to the intake extends ~1in into the can and has a flat end. The spring goes around this, and the diaphragm is the diameter of the overall can, sealed around the edges and has a steel plate at the center against which the spring bears and which fits against the intake port tube if you compress the spring. There is a small (~1/16") hole drilled in the rear cover to vent the back side of the diaphragm to the atmosphere. The spring is fairly weak, requiring only 1.3 lb to compress far enough for the diaphragm plate to seal against the intake tube.
Note the absence of any fancy oil separators or filtration stuff. Also note that the tube leading to the valley pan protrudes ~1/4" into the can, so there is no easy drain path for any accumulated oil to drain back to the crankcase.
Based on the construction, we can establish the functioning of the valve. With the back side of the diaphragm vented to atmosphere, the position of the diagram is going to be a function of the pressure within the can. A vacuum (relative to the outside atmosphere) is going to pull the diaphragm closed against the spring tension eventually closing off the intake port completely once a high enough vacuum is reached. Based on the size of the can and spring tension, a vacuum of ~3 in h20 within the can would cause the diaphragm to close off the port. Note however, that this *does not* mean that a 3 in vacuum in the intake closes it. The can connects to both the crankcase and the intake, and the crankcase pressure is always going to be higher than the intake due to blowby. So the pressure within the can is going to be higher than the intake vacuum. Exactly by how much is a a complex function of the flow rates and restrictions within the crankcase, but it's safe to conclude that valve is going to maintain crankcase pressure somewhere around 2 in h20 of vacuum.
Now remembering the above discussion, the normal operating vacuum of your intake is 2-5 in h20 if you have a healthy filter, so the CDR really does very little in normal operation. It's only really going to come into play with a clogged air filter or some other restriction.
Note the extreme simplicity of the valve - there is very little to wear out. Possibly the diaphragm could fail, or a very remote possibly of the spring breaking. A more likely failure would be for the vent port on the back of the valve to get plugged with paint or debris. Even then though, the effect of this failure is going to be pretty minimal unless you're running around with a horrible air filter.
So in conclusion, there is very little reason why one should need to replace a CDR valve, nor is there likely to be any issues running a road draft tube provided it doesn't cause crankcase pressure to be too high.
Further, there is no reason for the CDR to have anything to do with oil consumption. The only exception would be a bad CDR combined with another problem, ie a clogged air filter.
In support of this I note that nowhere in any of my extensive tech manual reading have I seen any mention of a maintenance requirement to change the CDR valve, nor any indication that one should look to it for an oil consumption problem.
My IH manual lists the following possible reasons for high oil consumption:
-Towing extremely heavy loads
-Improper operation, ie using the wrong gear range
-Plugged air cleaner
-Worn valve guides
-Worn piston rings
So bottom line, don't waste your money.
~John
First of all, the question is what is a cdr valve? CDR stands for crankcase depression regulator. It's the can located on the back of the intake on a stock motor and mounted on the valve cover or the air box in turbo motors. Physically it's about 4" diameter and 1 1/2" thick with a 1" hole in the front face of the can going to the intake and a ~1" tube coming from the bottom of the can going to the valley pan. Functionally it's the link between the crankcase and the intake and serves to vent crankcase vapors (blowby with a small amount of vaporized oil) into the intake so that they're burned. This is similar in function to the PCV system on a gasser, but rather different in implementation due to the design of a diesel.
From my Ford 'Diesel Engine Operations' training manual:
"Some engines use a more complicated [than a simple tube from the crankcase to the intake] crankcase emissions system with a crankcase depression regulator. In this system, crankcase vapors must go through the crankcase depression regulator to get into the intake system. This device is designed to maintain pressure in the crankcase as close to atmospheric pressure as possible. A high vacuum in the crankcase will tend to draw dirt from the outside through the front and rear seals. This will result in shortened seal life. In addition, high crankcase pressure may cause lube oil to be forced out of the gaskets and seals resulting in leaks."
It is interesting that high vacuum sucking up oil causing a runaway is not mentioned as a reason for fitting the CDR system. Also note that minimizing oil consumption is not mentioned.
On a gasser the PCV system connects into the intake side of the throttle, so there is always going to be a vacuum on one side of the PCV valve. For the reasons mentioned above, it's strongly desirable to maintain nearly atmospheric pressure in the crankcase. The PCV valve thus acts as a regulator to block the crankcase off from the high intake vacuum, especially under closed throttle. Typical intake vacuum on a gasser is 15-20 inhg.
In contrast, the intake on a diesel is under a minimum of vacuum, at least as long as the inlet is free flowing. There is a slight vacuum, but it's minimal. From what I can find, this is typically ~5 in h20 (note the different units) with a healthy air filter. Of note, IH specifies a max of 25 in h20 air filter restriction. This is equal to ~0.9 psi or ~1.8 in hg. That is, the absolute max worst case plugged air filter operating condition is some 20 times less intake vacuum than a gasser. A more normal full throttle operating condition would be ~0.1 psi/0.2 in hg of vacuum. This is somewhat less than the vacuum you creating sucking soda up a straw at mcdonalds.
So now let's look at the inside of this puppy.....
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Its very simple - exactly 2 parts within the can, a spring and a diaphragm. The port of the front of the can connecting to the intake extends ~1in into the can and has a flat end. The spring goes around this, and the diaphragm is the diameter of the overall can, sealed around the edges and has a steel plate at the center against which the spring bears and which fits against the intake port tube if you compress the spring. There is a small (~1/16") hole drilled in the rear cover to vent the back side of the diaphragm to the atmosphere. The spring is fairly weak, requiring only 1.3 lb to compress far enough for the diaphragm plate to seal against the intake tube.
Note the absence of any fancy oil separators or filtration stuff. Also note that the tube leading to the valley pan protrudes ~1/4" into the can, so there is no easy drain path for any accumulated oil to drain back to the crankcase.
Based on the construction, we can establish the functioning of the valve. With the back side of the diaphragm vented to atmosphere, the position of the diagram is going to be a function of the pressure within the can. A vacuum (relative to the outside atmosphere) is going to pull the diaphragm closed against the spring tension eventually closing off the intake port completely once a high enough vacuum is reached. Based on the size of the can and spring tension, a vacuum of ~3 in h20 within the can would cause the diaphragm to close off the port. Note however, that this *does not* mean that a 3 in vacuum in the intake closes it. The can connects to both the crankcase and the intake, and the crankcase pressure is always going to be higher than the intake due to blowby. So the pressure within the can is going to be higher than the intake vacuum. Exactly by how much is a a complex function of the flow rates and restrictions within the crankcase, but it's safe to conclude that valve is going to maintain crankcase pressure somewhere around 2 in h20 of vacuum.
Now remembering the above discussion, the normal operating vacuum of your intake is 2-5 in h20 if you have a healthy filter, so the CDR really does very little in normal operation. It's only really going to come into play with a clogged air filter or some other restriction.
Note the extreme simplicity of the valve - there is very little to wear out. Possibly the diaphragm could fail, or a very remote possibly of the spring breaking. A more likely failure would be for the vent port on the back of the valve to get plugged with paint or debris. Even then though, the effect of this failure is going to be pretty minimal unless you're running around with a horrible air filter.
So in conclusion, there is very little reason why one should need to replace a CDR valve, nor is there likely to be any issues running a road draft tube provided it doesn't cause crankcase pressure to be too high.
Further, there is no reason for the CDR to have anything to do with oil consumption. The only exception would be a bad CDR combined with another problem, ie a clogged air filter.
In support of this I note that nowhere in any of my extensive tech manual reading have I seen any mention of a maintenance requirement to change the CDR valve, nor any indication that one should look to it for an oil consumption problem.
My IH manual lists the following possible reasons for high oil consumption:
-Towing extremely heavy loads
-Improper operation, ie using the wrong gear range
-Plugged air cleaner
-Worn valve guides
-Worn piston rings
So bottom line, don't waste your money.
~John
