The CDR (Crankcase Depression Regulator) System

The CDR (Crankcase Depression Regulator) and the connecting system is extremely important in maintaining a good running 6.5. By design, crankcase emissions are routed into the turbo intake and harmlessly burned in the cylinders of the engine. The CDR also controls crankcase pressure, causing a slight vacuum in the crankcase while the engine is running. This vacuum helps to prevent oil leaks.

The CDR is located on the passenger-side valve cover. GM recommends replacement of the CDR at 100,000 intervals. Commonly, these must be cleaned or replaced more often. We suggest that the CDR system be checked once each year.

Testing the function of the CDR is easy to do. Simply remove the oil dip-stick and install a 4-5 foot long section of clear 3/8" id tubing onto the dip-stick tube. Drape the tube over the fender of the truck and into a container of water.

Start the engine. When this are working properly and there is vacuum in the crankcase, water will be pulled up into the clear tubing. Typically, at idle and with a healthy CDR, the water will rise in the tube by 1/16" to 1/2". When you rev the engine to 2000 rpm, the water will rise in the tube 1/2" to 1".

If the CDR is malfunctioning, there will be pressure in the crankcase and water will be pushed down in the tube and may even blow bubbles in more extreme cases.

If the tube blows bubbles, this is an indication of a malfunctioning CDR or excessive blow-by leakage of the cylinders. This tube and water container test, is a great pre-purchase inspection.

In some cases, the CDR can be cleaned successfully. Cleaning can be accomplished by soaking overnight in kerosene, diesel or safety-clean solvent. Do not use anything more harsh than these, as damage to the diaphragm will result. The cleaning agent must be completely removed prior to re installation. We use warm, soapy water and flush with clean water, making certain that all water is removed prior to re installation. Do not use compressed air to dry the CDR, as damage to the diaphragm can easily result.

It is critically important that the CDR mount rubber and all connecting tubes be in good condition.

Questions about this or any Heath Diesel product? Feel free to contact us anytime 1-877 894 6266 or sales@heathdiesel.com

- Bill Heath

Related Links:
GM 6.5 Diesel Parts