gmctd
07-17-2004, 10:56 AM
The CDR cannister, affectionately known as the "tuna can", is a Positive Crankcase Ventilation system for Diesels.
It provides regulated low-vacuum, about 1" at idle to 4 to 6 inches WC at full load, from the engine air intake path to remove blow-by gases from the crankcase, and prevent oil leaks.
The PCV valve is designed for engines with a throttle plate across the air inlet path, which causes high vacuum in the intake manifold. High at idle, vacuum will decrease under load, as the throttle is opened, but will greatly increase during vehicle deceleration, when the throttle plate is closed.
The PCV device is a small two-level valve, for both normal and deceleration vacuum levels, and is part of a fresh-air ventilation system. It usually contains a spring tailored to engine size to ensure shuttle valve closure, which works in conjunction with shuttle weight against gravity.
The system must be ported to fresh air because valve guide and piston ring blow-by are not (hopefully) higher than vacuum demand, typically 20" at idle, which would draw air, dirt, water,oil, etc, thru the various engine seals without the filtered fresh air source in the air filter housing.
The Diesel engine, on the other hand, generates vacuum under opposite conditions - almost none at idle, more as engine speed increases. Diesels have no throttle plate to restrict intake air flow.
Diesel vacuum is caused by the slight restrictions presented by the air filter and intake path ducting.
A turbocharger increases available vacuum even more, as the compressor draws more air to the inlet under engine load, to produce Boost.
Dirty air filter restriction will increase inlet vacuum in turbo and intake vacuum in non-turbo engines.
The CDR is specifically calibrated for turbo or non-turbo engines, with normal filter deterioration from dirt and dust factored in.
With no great levels of vacuum to draw-thru the crankcase, no fresh air source is needed - it is a closed-crankcase system.
Normal blow-by is low, so vacuum must be regulated such that air is not drawn into the engine thru various seals - crankshaft, valve-stem, oil filler and dipstick tubes. The crankshaft seals assume greatest importance because of location down low in road draft area.
The CDR, Crankcase Depression Regulator, is designed to function with low-level vacuum. The tuna-can size is to accomodate the large silicone rubber\synthetic diaphragm. Vacuum on the diaphragm actuates the valve against a low-pressure spring, calibrated for turbo or non-turbo applications, which also functions to ensure that the valve opens as vacuum decreases.
Fully open at idle, it will begin to close as power demand and vacuum increases, regulating the 'depression' in the crankcase such that excessive oil is not drawn out of the engine, and blow-by pressure in the crankcase does not increase.
It is not a one-way valve, but closure is toward the vacuum source. It opens under crancase 'back-fire' conditions, and would become a 'no-way' valve if the diaphragm ruptured, allowing excessive vacuum to develop in the crankcase.
Because blow-by vapor is drawn into the turbo inlet, oil will accumulate in the inlet area, but is not cause for concern unless the quantity approaches a quart a month. Excess vapor from worn piston rings can cause engine surging, as vapor is drawn into cylinder and ignited along with injected fuel, which is a light oil.
Non-Diesel oils vaporize more easily due to higher pressures and temperatures encountered in Diesel service, particularly those in the turbocharger housing.
<><><><><><><><><>CDR TESTING<><><><><><><><><>
CDR testing can be accomplished with 4' section of clear plastic tubing, sized to fit the dipstick tube, ~3/8".
Form a 3" U-bend , with 12" vertical columns. This could be attached to a piece of 1 x 6 with large u-staples, parallel-spaced at one inch intervals for indication of measurement.
Important - do not crush or deform the plastic tubing.
Place the free end over the dipstick tube, ensuring tight fit, with no leak-by. Position the manometer vertically, where the upper end of the U is lower than the end over the dipstick tube.
Note: this is to prevent water siphoning into the oil pan thru the dipstick tube.
Pour colored water into the U section such that about 6 " of water is in each leg, about 4 - 6" below the top of the open end.
Have someone start the engine, bring the rpm up to about 2000, keeping close watch on the water level in the U-tube. If the water in the dipstick leg rises an inch, the water in the open leg will drop an equal amount. Adding the drop level to the rise level, this would indicate vacuum at two inches on the Water Column.
Vacuum at idle should be around 1", depending on air filter restriction; at 2000 rpm, the CDR should limit vacuum to 4 - 6" WC on a calibrated Manometer. The shade-tree version should indicate close to those figures, depending on accuracy of staple intervals.
If the level in the dipstick leg drops, and the open leg level rises, this indicates the crankcase is slightly pressurized.
27" WC is equal to 1 PSI (Pound per Square Inch) 1psi is equal to 2" mercury
Atmospheric pressure is 14.7 psi, or 29" mercury, or 396" WC, rounding off
<><><><><><><><><><><><><><><><><><><><><><><>
The CDR should never be solvent-cleaned, as various solvents can dissolve the diaphragm, again resulting in a 'no-way' valve.
Some truck manuals indicate replacment at 30,000 miles. This refers to the early style CDR and oil-cap breather system, used up through mid-'80s. By '88 - '89, the CDR system had been revised to its present configuration, where the CDR cannister is on the passenger-side valve cover, with one external connecting hose to the intake system.
Early failure-prone systems can be easily upgraded to the late setup - 1 valve cover with grommet seal, 1 CDR, 1 hose.
Replace the CDR in the late systems when it fails the Manometer water column test.
It provides regulated low-vacuum, about 1" at idle to 4 to 6 inches WC at full load, from the engine air intake path to remove blow-by gases from the crankcase, and prevent oil leaks.
The PCV valve is designed for engines with a throttle plate across the air inlet path, which causes high vacuum in the intake manifold. High at idle, vacuum will decrease under load, as the throttle is opened, but will greatly increase during vehicle deceleration, when the throttle plate is closed.
The PCV device is a small two-level valve, for both normal and deceleration vacuum levels, and is part of a fresh-air ventilation system. It usually contains a spring tailored to engine size to ensure shuttle valve closure, which works in conjunction with shuttle weight against gravity.
The system must be ported to fresh air because valve guide and piston ring blow-by are not (hopefully) higher than vacuum demand, typically 20" at idle, which would draw air, dirt, water,oil, etc, thru the various engine seals without the filtered fresh air source in the air filter housing.
The Diesel engine, on the other hand, generates vacuum under opposite conditions - almost none at idle, more as engine speed increases. Diesels have no throttle plate to restrict intake air flow.
Diesel vacuum is caused by the slight restrictions presented by the air filter and intake path ducting.
A turbocharger increases available vacuum even more, as the compressor draws more air to the inlet under engine load, to produce Boost.
Dirty air filter restriction will increase inlet vacuum in turbo and intake vacuum in non-turbo engines.
The CDR is specifically calibrated for turbo or non-turbo engines, with normal filter deterioration from dirt and dust factored in.
With no great levels of vacuum to draw-thru the crankcase, no fresh air source is needed - it is a closed-crankcase system.
Normal blow-by is low, so vacuum must be regulated such that air is not drawn into the engine thru various seals - crankshaft, valve-stem, oil filler and dipstick tubes. The crankshaft seals assume greatest importance because of location down low in road draft area.
The CDR, Crankcase Depression Regulator, is designed to function with low-level vacuum. The tuna-can size is to accomodate the large silicone rubber\synthetic diaphragm. Vacuum on the diaphragm actuates the valve against a low-pressure spring, calibrated for turbo or non-turbo applications, which also functions to ensure that the valve opens as vacuum decreases.
Fully open at idle, it will begin to close as power demand and vacuum increases, regulating the 'depression' in the crankcase such that excessive oil is not drawn out of the engine, and blow-by pressure in the crankcase does not increase.
It is not a one-way valve, but closure is toward the vacuum source. It opens under crancase 'back-fire' conditions, and would become a 'no-way' valve if the diaphragm ruptured, allowing excessive vacuum to develop in the crankcase.
Because blow-by vapor is drawn into the turbo inlet, oil will accumulate in the inlet area, but is not cause for concern unless the quantity approaches a quart a month. Excess vapor from worn piston rings can cause engine surging, as vapor is drawn into cylinder and ignited along with injected fuel, which is a light oil.
Non-Diesel oils vaporize more easily due to higher pressures and temperatures encountered in Diesel service, particularly those in the turbocharger housing.
<><><><><><><><><>CDR TESTING<><><><><><><><><>
CDR testing can be accomplished with 4' section of clear plastic tubing, sized to fit the dipstick tube, ~3/8".
Form a 3" U-bend , with 12" vertical columns. This could be attached to a piece of 1 x 6 with large u-staples, parallel-spaced at one inch intervals for indication of measurement.
Important - do not crush or deform the plastic tubing.
Place the free end over the dipstick tube, ensuring tight fit, with no leak-by. Position the manometer vertically, where the upper end of the U is lower than the end over the dipstick tube.
Note: this is to prevent water siphoning into the oil pan thru the dipstick tube.
Pour colored water into the U section such that about 6 " of water is in each leg, about 4 - 6" below the top of the open end.
Have someone start the engine, bring the rpm up to about 2000, keeping close watch on the water level in the U-tube. If the water in the dipstick leg rises an inch, the water in the open leg will drop an equal amount. Adding the drop level to the rise level, this would indicate vacuum at two inches on the Water Column.
Vacuum at idle should be around 1", depending on air filter restriction; at 2000 rpm, the CDR should limit vacuum to 4 - 6" WC on a calibrated Manometer. The shade-tree version should indicate close to those figures, depending on accuracy of staple intervals.
If the level in the dipstick leg drops, and the open leg level rises, this indicates the crankcase is slightly pressurized.
27" WC is equal to 1 PSI (Pound per Square Inch) 1psi is equal to 2" mercury
Atmospheric pressure is 14.7 psi, or 29" mercury, or 396" WC, rounding off
<><><><><><><><><><><><><><><><><><><><><><><>
The CDR should never be solvent-cleaned, as various solvents can dissolve the diaphragm, again resulting in a 'no-way' valve.
Some truck manuals indicate replacment at 30,000 miles. This refers to the early style CDR and oil-cap breather system, used up through mid-'80s. By '88 - '89, the CDR system had been revised to its present configuration, where the CDR cannister is on the passenger-side valve cover, with one external connecting hose to the intake system.
Early failure-prone systems can be easily upgraded to the late setup - 1 valve cover with grommet seal, 1 CDR, 1 hose.
Replace the CDR in the late systems when it fails the Manometer water column test.