Best Practices for Replacing EGR Cooler and Oil Cooler

One of the biggest headaches reported by diesel car and truck owners is the EGR (Exhaust Gas Recirculation) cooler and the oil cooler.

Replacing these items can seem challenging. There are various ways to do it, but, if you follow some of the best practices listed here, the job will not be as bad as you may have anticipated.

What Do the EGR and Oil Cooler Do?

The EGR and oil cooling systems do exactly as the name implies: cool the exhaust and oil system in your diesel car or truck. Many misidentify the EGR and oil coolers with the small auxiliary coolers, often mounted on the front of your vehicle, as is the case with Ford diesel cars and trucks.

The EGR and oil cooling systems are much larger and are integrated somewhere near your oil filter in the engine compartment.

Why Do EGR Coolers Malfunction?

EGR system

EGR coolers often malfunction due to the buildup of dirt, gunk, and other material in the oil cooling system. The coolant flows through the very small diameter tubes in the engine compartment, catching and trapping large particles that may be suspended in the coolant. This eventually, usually around 50,000 miles or so, clogs the system enough so the coolant can no longer travel through the channels.

Since the oil coolant system flows through the EGR system too, the EGR system malfunctions as well. Therefore, if one fails, they both fail and both need replacement.

How Can I Tell When the Systems Are Failing?

Three things may start to happen which indicate that your EGR and oil cooling have begun to fail:

  1. There’s an unexplained loss of coolant from your overflow or degas bottle in the cooling system.

Just because you can’t see any puddles of fluid does not mean it is not leaking. The coolant may simply leak back into the exhaust system.

  1. There’s white smoke.

White smoke coming out of your tailpipe is not really smoke. It’s steam. The coolant that leaks into the exhaust system heats up quickly and vaporizes, turning to steam and exiting through your tailpipe.

  1. There’s an overflowing degas bottle.

This indicates a clogged engine coolant system, which has restricted the flow of coolant through the EGR, hence backing it up. This makes it heat up inside the exhaust system, and start boiling or bubbling out of your degas bottle.

MAP Sensor and the EGR Cooling System

MAP sensor

The Manifold Absolute Pressure (MAP) sensor senses the variations in your manifold pressure. The carbon grit and dirt that build up in the oil cooler system and the EGR cooling system can clog and cause the MAP to malfunction.

When this happens, your mileage will start to drop, and the engine will not accelerate as quickly.

While this may happen well before the EGR and oil cooling systems fail, nevertheless it is an indicator that the gunk and grime have begun to build up in the engine.

The fix for a malfunctioning MAP, unlike that for a malfunctioning EGR cooling system, is simple. Remove the MAP, clean off the dirt and grime, and reinstall it.

Best Practices: The Steps

Step #1

The first step when you diagnose a failed EGR and oil cooling system is to replace the EGR cooler. You do not want to flush the cooling system first. If you flush the system while you still have a failed EGR, the fluid may leak into the cylinders, causing a busted head gasket or a hydro lock.

Step #2

Once you replace the EGR cooling system, you need to flush it out. Use Cascade liquid detergent or whatever the manufacturer recommends. You need to get as much gunk, dust, and other particles out of the system as possible.

Keep flushing until the rinse runs clear.

Step #3

Flush out the radiator. If you are doing the job yourself, you should pull it out entirely and take it to a radiator shop for cleaning and back-flushing.

Step #4

After you have replaced the EGR and flushed out the system, you can replace the oil cooling system.

Step #5

Once you have replaced both systems, re-install the now clean radiator and put in a new coolant bypass filter.


Replacing the EGR and oil cooling systems can be an expensive repair, and many diesel vehicle owners find it much more cost-effective to do it themselves.

However, you can cause more problems if you are not careful in how and in what order you perform the removals and replacements.

If you follow these best practices and swap out the systems in the order and manner indicated here, you will have lessened the risk of creating more problems for yourself and will get your diesel back on the road.


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